If your Toyota Prius has a humming noise at high speed, it can be distracting and, depending on the cause, dangerous.

We’ve outlined the most common reasons why a humming noise in your car gets louder with speed. We’ve also provided an audio sample of each issue to help determine what’s causing the hum. 

Toyota Prius Humming at High-Speed: Quick Info

How to Tell the Difference Between a Bad Wheel Bearing and Bad Tire

Bad wheel bearings and bad tires have a similar sound. You can tell them apart in most cases by doing this simple test on your Toyota Prius:

1. Drive your car at the slowest speed it takes to reproduce the humming noise.
2. Wiggle the steering wheel back and forth. You’re looking to change your Prius’s load balance from one side to the other.
3. Did the sound change as you moved the wheel? If it did, your car likely has a faulty wheel bearing. If it didn’t change, it’s likely a tire-related problem.

If you suspect a bad wheel bearing, jack your Prius up and free-turn each wheel. If one sounds gritty, that wheel bearing will likely need replacing.

1. Defective Wheel Bearing

A defective wheel bearing is a very common reason your Prius will make a humming noise while driving. Here’s what a bad wheel bearing sounds like:

A bad wheel bearing can cause a humming sound. If your Prius has a worn wheel bearing, the sound will be slightly more high-pitched than a tire issue (you can play that sound below).

You can test all four wheel bearings when the car is stationary. Jack up each wheel and spin it freely. If the wheel sounds “gritty” and is hard to turn, you likely found the humming sound’s cause.

You can also use the method outlined above, where you rock your Prius while it’s moving to see if there is a change in pitch. If there is, you’re usually looking at a worn wheel bearing and not a bad tire.

2. Tire Issues

Here’s the sound of a cupped tire:

If your Toyota Prius is suffering from uneven tire wear, you should be able to pick up the noise while driving around 30 MPH with it getting louder as you accelerate.

With uneven tire wear, you may also notice:

Wheel Out of Balance

If your Prius’s wheels are not correctly balanced, it can cause a humming noise when driving.

Tires are balanced with wheel weights when a new tire is installed. Balancing corrects any vibration before the tires go on the vehicle. Take a look behind the wheels. You can usually tell if a wheel weight fell off.

See the wheel weight above? Depending on where they are needed, they can be on the front or back of your Prius’s wheels. You’ll likely see the spot where the wheel bearing was.

Cupping

Tires that are “cupped” or “scalloped” have uneven tread wear across the tire. Run your hand along the tread. If it’s cupped badly enough, you’ll feel the unevenness.

The following suspension issues usually cause cupping:

• Bad shocks/struts
• Bad ball/cv joints
• Poor wheel alignment

If you find cupping on the inside tread of your Prius’s tire, suspect an issue with the wheel alignment.

If the cupping is on the outside tread, it still could be an alignment issue. But it’s more likely your Toyota Prius has a suspension problem. Here’s more from Atlantic Motor car on cupping. Or, you can watch the video below. It picks up at the exact point where you can see what cupped tread looks like.

Large Tire Tread

A humming noise is normal if you’ve recently replaced your Prius’s tires with an aggressive tread.

Off-road and snow tread tires are notorious for making a loud humming sound.

Other Causes

A bad wheel bearing or suspension issue are the most common causes of humming when driving on the highway in the Toyota Prius. Here are some other things that can cause noise while at speed:

• Brakes– If the brakes have worn past their squealers, they’ll make noise at highway speed. The problem is, the noise is AWFUL. It feels like grinding. It can come and go depending on the wheel’s angle and the vehicle’s speed. 
• Power Steering– A bad power steering pump can make a humming sound. The only problem is that it should be heard at any speed. You may only be noticing it while your Prius is moving. Try revving the engine while in Park and seeing if that creates the humming noise.

Conclusion

You can do a few simple tests to figure out what is causing a humming noise while driving at high speed in your Toyota Prius. It’s not a breakdown risk, but you can still end up stranded if the wheel bearing or suspension component causing the hum fails.

P0073 is a common OBD2 trouble code that can affect the Toyota Prius. OBD2 trouble codes. In layman’s terms, it indicates that there is an issue with your car’s ambient air sensor.

The ambient air temperature sensor (or AAT for short) is responsible for monitoring outside air temperature and regulating your vehicle’s automatic climate control system.  It doesn’t affect the way your car runs or drives at all.

While P0073 is a generic code (it has the same meaning for all vehicles made after 1996), repair steps will vary depending on your Toyota Prius’s model year and equipped options.

P0073 Quick Info

Definition

The Diagnostic trouble code (DTC) P0073 stands for “Ambient Air Temperature Sensor Circuit High Input.”

• P: Powertrain
• 0: Generic Code Type
• 0: Sub-System
• 73: Specific Malfunctioning Identifier

Here’s the definition of P0073 for the Toyota Prius broken down into its two main parts:

1. Ambient Air Temperature (AAT) Sensor

The AAT sensor measures the air temperature outside of the car’s cabin. It converts this signal to a voltage value the Powertrain Control Module (PCM) can read.

Depending on your Prius’s model year and options, the AAT’s only function may be to display the outside air temperature.

If your particular vehicle is equipped with a climate control system that automatically adjusts itself, it can affect the cabin air temperature (particularly when the auto start function is engaged).

2. Circuit High

The voltage value being returned by the AAT is too high in relation to the voltage value of the Intake Air Temp sensor and/or the Engine Coolant Temp sensor. These three should be within a few degrees of one another if your Prius is completely cold.

P0073 Symptoms: Toyota Prius

Here are the most common symptoms associated with P0073 in the Toyota Prius:

• Malfunction Indicator/Check Engine Light has lit up
• Air Conditioning may not work
• The instrument cluster (dashboard) may not display the correct outside temperature
• The overhead compass/console may not display the correct outside temperature

P0073 Causes + Diagnosis: Toyota Prius

There are really two main causes of P0073 in the Toyota Prius. Either the AAT is bad, or there is a problem with the wiring harness going to it.

• Malfunctioning ambient air temperature sensor
• Faulty Powertrain Control Module (Not very common)
• A damaged or corroded electrical connector
• Damage to the AAT sensor signal circuit

Most of the time, P0073 is going to be caused by a bad AAT sensor or AAT sensor wiring.

On most vehicles, the AAT sensor can be found around the front grill or bumper. Here’s a good order to go about diagnosing P0073 in your car.

1. Check the AAT Wiring

You should start by looking at your Prius’s Ambient Air Temperature (AAT) sensor, connection, and wires.

If the AAT wiring harness is damaged (which frequently happens due to its location), repair it and see if that clears the code.

You can read these things using a Digital Volt-Ohm Meter (DVOM) and a thermometer. Check the vehicle manual for proper readings, and if they differ significantly from your readings, replace the sensor.

You can find the correct readings inside or very close to the front bumper.

2. Check the AAT Sensor Itself

Now that you’ve checked your Prius’s AAT wiring, it’s time to check the sensor itself.

Follow through with and eliminate any other error codes before focusing on P0073. Examine the sensor itself to ensure it doesn’t look physically damaged.

In some cases, repositioning or cleaning out the terminals is the solution, but typically the culprit is a connection issue or bad sensor, whether it’s exposed or burnt wires. 

It’s likely you’ll need to replace the sensor itself, which is usually around $20 or so.

How Serious is a P0073 Code?

P0073 should not be considered a breakdown risk in the Toyota Prius.

This code will not affect the engine, steering, brakes, fuel consumption, or your car’s overall ability to go from point A to point B.

What it will cause, is an inconvenience. The lack of air conditioning and the inability to read the outside temperature could become a major nuisance for those located in areas with hotter climates.

The number one thing P0073 affects is the auto start features climate control. If it’s hot out, the A/C will kick on. If it’s cold, the PCM will activate the heater. Most vehicles still allow you to manually control the A/C if there is an issue.

Conclusion

Replacing the AAT sensor will likely clear P0073 in the Toyota Prius, but checking the wiring harness for damage first can save time and aggravation.

P0088 is a common OBD2 trouble code that can occur in the Toyota Prius. In layman’s terms, it indicates that your car’s fuel pressure is too high.

While P0088 is a generic code, repair steps will vary depending on your Prius’s model year, engine type, and how it regulates fuel pressure.

P0088 Definition: Fuel Rail/System Pressure – Too High

P0088 is a generic powertrain code that indicates a fuel pressure issue. This code is set when your Prius’s PCM detects too much pressure in the fuel system.

Fuel Rail/System Pressure

The purpose of the pressure monitoring system is to help the engine run by monitoring the fuel pressure from the fuel injection system. Too much fuel can lead to just as many problems as no fuel.

Too High

If the fuel pressure is too high (the voltage value coming from the fuel pressure sensor is over the maximum value), it signals your Prius’s PCM to display code P0088. Several components make up the fuel system. If any of them are faulty, it could cause a code P0088.

The main components that can fail and cause P0088 are the fuel pump, fuel pressure regulator, and fuel pressure sensor. Knowing how your car’s fuel pressure is regulated can help you figure out the faulty component.

There are two ways that an engine can have its fuel pressure regulated.

1. The first way is to use a fuel pressure regulator, which returns the extra pressure to the fuel tank.
2. The other way is that the fuel pressure is regulated by the fuel pressure sensor, as it works with the PCM. The fuel pump can adjust to the needs of the engine directly, with no regulator needed. The fuel pressure sensor signals the pressure in the fuel rail to the PCM. If it’s not working correctly, the engine may stall or run rough.

P0088 Symptoms: Toyota Prius

There will almost ALWAYS be symptoms associated with P0088 if the fuel pressure is incorrect. There may not be any symptoms if the fuel pressure sensor is bad.

Here are the common symptoms associated with P0088 in the Toyota Prius:

• Slow/no start
• Decreased fuel mileage
• Misfiring (you’ll likely see code P0300, focus on P0088 first)
• Fouled spark plugs
• Stalling
• Black exhaust smoke

P0088 Causes 

Here are the most common causes of P0088 in the Toyota Prius:

• Bad fuel pressure regulator
• Bad fuel pressure sensor
• Bad fuel pump
• Wiring issues at the fuel pressure sensor
• PCM

Toyota Prius P0088 Diagnosis

While several things can cause the P0088 code in the Toyota Prius, here’s a good order to diagnose them in:

Inspect the Fuel Pressure Sensor Wiring

Start here (particularly if your Prius is running fine).

Take a look at the fuel pressure sensor wiring. Make sure that it is not burnt, cracked, or frayed. Due to its location, damage to the harness is very common. It’s not uncommon for a rodent to nest around the intake, particularly in the wintertime.

Make sure that the harness is plugged into the sensor tightly and that there are no damaged pins inside the connector. If there are, you’ll need to repair or replace the harness.

Check Fuel Pressure

Be careful when checking your Prius’s fuel pressure. It’s always best to do it with the engine cold. Make sure you have a fire extinguisher ready in case the fuel sprays. Do not connect or disconnect the fuel pressure gauge with the engine on.

The next course of action when diagnosing P0088 is to test the actual fuel pressure at the fuel rail. You’ll need a manual fuel pressure testing gauge. That’s not a tool that most Shadetree mechanics have, you can usually rent one or borrow one from the local parts store.

You’ll need to look up the exact fuel pressure for your vehicle and engine combination. If the fuel pressure checks out, you likely have a bad fuel pressure sensor.

If the fuel pressure is too high, you’ll need to replace the fuel pressure regulator.

Check the Fuel Pump

A returnless fuel pump can cause P0088. You’ll need to verify what type of fuel system your particular Toyota Prius has.

Using a multimeter, check the resistance of the fuel pump by connecting the positive lead to the positive terminal on the pump and the negative lead to the negative terminal.

Conclusion

Fixing P0088 in the Toyota Prius involves determining whether or not the fuel pressure is really too high or if the sensor is bad. If the pressure is too high, it can only be a few things that cause the issue.

P0152 is a common OBDII code that occurs in many vehicles, including the Toyota Prius. It indicates that the bank 2 sensor 1 O2 sensor is reporting a voltage level that is higher than its normal operating range.

P0152 Definition: O2 Sensor – High Voltage – B2S1

O2 Sensor

Oxygen sensors are responsible for metering the exhaust as it exits the engine. This allows the PCM (Powertrain Control Module) to adjust the air/fuel ratio constantly, which helps your Prius’s engine run at optimum efficiency.

High Voltage

P0152 is triggered when your Prius’s PCM detects the following conditions:

• The voltage at the B2S1 O2 sensor remains above the voltage threshold for 20 seconds or more.
• The air-fuel sensor stays in rich biased mode for too long.

There are also some less likely problems that can cause P0152. We’ll go over those below.

Bank 2 Sensor 1

• Bank 2 is the side of the engine with the second cylinder.
• Sensor one is the first sensor in line as the exhaust leaves the head. It’s on or right after the exhaust manifold.

Toyota Prius P0152 Symptoms

If your Prius has P0152, there are usually noticeable symptoms. They include:

• Rough running engine
• Smelly exhaust
• Service engine soon light on
• Poor MPG

Most of the time, it’s not a breakdown risk. But, like anything that causes the service engine soon light to come on, it is a good idea to have it fixed as soon as possible. A poor air fuel mixture going through the catalytic converter can damage it.

Toyota Prius P0152 Causes 

Here are the most common issues that cause the P0152 code in the Toyota Prius. They are presented in order (somewhat) from most to least likely to cause the problem.

• Bad Oxygen Sensor– The O2 sensor itself is one of the most likely reasons that P0152 is triggering your service engine soon light. Although it is a temptation to replace it right away, it wouldn’t hurt to check out the wiring harness around it beforehand.
• Wiring Harness Issues- The wiring that goes to the front and rear oxygen sensors is very susceptible to damage. This is due to the fact that O2 sensors are under the chassis, where they are subject to punishment from road debris, and exhaust heat. Here’s how to find a short in the wiring harness (Youtube).
• Damage to the Terminal– The terminal that the oxygen sensor connects to (the plug) is also relatively susceptible to damage. You’ll want to make sure that there is voltage going to it. There’s more on that directly below.
• Wrong O2 Sensor– If you are getting P0152 after having recently replaced your Oxygen sensor, it may be that the replacement is wrong or bad.

Prius P0152 Diagnosis

Here is a fantastic video that covers all aspects of diagnosing the P0152 code:

Swap Test (Easy to Do At Home With Simple Tools)

You can perform the swap test by swapping the bank 1 and bank 2 oxygens sensors. Clear the code and see if it changes to P0132 (the bank 1 side of this code). If it does, you need to replace the oxygen sensor that was just swapped from bank 2.

Using a Multimeter

This video is for P0132, but is completely relevant for P0152

It is possible to diagnose the P0152 with a multimeter. If you use the multimeter, you’ll know whether or not the voltage coming to and from the oxygen sensor is within spec, this can help you determine if it’s your Prius’s O2 sensor or wiring harness that’s the issue.

If you don’t have access to a multimeter, it certainly wouldn’t hurt to check the wiring to between the fuse box and the Oxygen sensor first. If it ends up being a wiring issue, it’ll save you money over buying an unnecessary O2 sensor.

You can also use a voltage test light to determine whether or not the oxygen sensor is getting any voltage at all (they’re about $5 at Walmart).

If it’s not getting any voltage, attach the test light to the harness plug and shake the wiring a little bit. If the light comes on, even for a second, you know that you have a short circuit causing the P0152 trouble code.

Conclusion

Good luck finding whatever caused P0152 in your Toyota Prius. It’s usually caused by a bad O2 sensor. Since there are two “banks”, you can use the swap test for a quick and easy diagnosis.

P0501 is an OBD2 trouble code that indicates there is an issue with your Toyota Prius’s Vehicle Speed Sensor (VSS). It occurs when the Powertrain Control Module (PCM) gets a signal from the VSS outside its normal operating range (in terms of voltage).

P0501 is a generic powertrain code, which means it has the same definition for the Toyota Prius as all vehicles made after the 1996 model year.

Note: If you have gotten P0501 right after changing your Prius’s tire size, it’s likely the PCM needs to be recalibrated for the change in size.

P0501 Definition: VSS – Range/Performance

P0501 is a pretty easy code to understand. Here are both parts of its definition for the Toyota Prius:

Vehicle Speed Sensor

The VSS has two main functions.

1. The first is to provide data to the speedometer. It’s not uncommon for the speedometer to be erratic or unmoving when a vehicle has P0501.
2. The second function of the VSS is to provide speed data to the PCM. The PCM needs to know how fast your Prius is moving to support many vital functions. The traction control system, cruise control, ABS, and even transmission shift points all need VSS data to work.

The VSS can be located on the transmission tail shaft, around the wheel hub, or (on older models) be integrated with a mechanical speedometer. Where it’ll be located on your vehicle will depend on the make, model year, and transmission type.

Range/Performance

The signal coming from the VSS is not within its normal operating range. The voltage could be erratic, too high, or too low.

Toyota Prius: P0501 Symptoms

Here are the most common symptoms of P0501:

• Check engine light
• Limp mode
• Erratic shifting (likely shifting too early)
• ABS light
• Traction control light
• Speedometer not working properly

If the ABS and traction control lights are on, and P0501 is the only code stored in your PCM’s memory, fixing the code’s cause should turn them off.

Toyota Prius: P0501 Causes and Diagnosis

Here are the most common causes of P0501 in the Toyota Prius and a good order to check them in. The exact repair steps will depend on the transmission and model year of your vehicle.

1. Check For Other Codes

The first thing you should do is document all trouble codes and data before touching anything.

It’s likely another code may shed more light on what’s going on. If the VSS voltage is too low, you may also get P0502. If it is too high, you’re likely to see P0503. That’s a good starting point.

2. Inspect the VSS Wiring

Next, locate your Prius’s VSS and inspect the wiring harness going to it. You are looking for broken, or frayed wiring. Wiring issues are a very common cause of P0501. If any wiring looks bad, repair it and clear the code.

3. Check the Sensor Voltage

Check the voltage at the VSS sensor. If it is within factory specs, it’s likely that the VSS sensor has gone bad and needs to be replaced.

Conclusion

The good news with P0501 in the Toyota Prius is that there aren’t many common causes. Replacing the VSS is far and away the most common fix. Good luck repairing your vehicle!

P0725 is a common OBD2 code that can occur in the Toyota Prius. It indicates an issue with the engine speed sensor input circuit (which measures the engine speed at the input shaft and helps the PCM determine when and how hard to shift the transmission).

It’s a generic code, which means it has the same meaning for the Prius as it would any other vehicle. Exact repair steps will depend on your Toyota’s model year and transmission type.

P0725 Definition: Engine Speed Input (Sensor) – Circuit Malfunction

Engine Speed Input Sensor

The engine speed input sensor is responsible for relaying data to your Prius’s PCM on how fast the engine turns. It can be referred to as the transmission input speed sensor, input speed sensor, or engine speed input sensor.

On most Transmissions, it screws into the case near the front of the input shaft. A relcutor wheel turns with the input shaft, and the engine input speed sensor uses an electromagnetic field to measure how fast it is turning.

Circuit Malfunction

Your Toyota Prius’s engine speed input circuit sends data that it receives from the input speed sensor back to the PCM in the form of a voltage value. It’ll compare this value to the engine RPM, output speed sensor, and throttle position.

When the voltage value is not theoretically correct when compared to the other sensors, P0725 is stored in the PCM’s memory.

Toyota Prius P0725 Symptoms

While P0725 is not typically a full breakdown risk, there will usually be very difficult to drive. Here are the most common symptoms your Prius may experience:

• Check engine light
• Speedometer and tachometer not working properly (or at all)
• Transmission not shifting properly
• Not all gears are available, and harsh shifts (limp mode)

Toyota Prius P0725 Causes + Diagnosis

Here are the most common causes of P0725 in the Toyota Prius:

Dirty or Low Transmission Fluid

Since P0725 is a transmission-related trouble code. The first thing you should do is check the transmission fluid color. If it’s brown, black, or gray, there could be a transmission problem.

If there are metal flakes in the transmission, it can cause the input speed sensor to stop picking up the reluctor wheel.

Speed Input Sensor Wiring Issue

After confirming that your Prius’s transmission fluid is in good shape and properly filled, the next easiest thing to check is the wiring harness coming from the input speed sensor.

Check the harness for cracks or damage. If it appears damaged, replacing it may clear P0725.

Inspect the pins where it plugs into the speed input sensor. If the pins are damaged or corroded, you’ll either need to clean/replace them or repair the harness.

Bad Input Speed Sensor

A bad input speed sensor is the most common cause of P0725. Before replacing it, inspect it to see if there are any metal shavings on the magnetic tip.

Other Causes

Here are some other causes of P0725:

• Transmission Failure: If your Toyota Prius has a transmission that is slipping, it can create metallic debris that affects the input speed sensor.
• Bad PCM: This rarely happens but has been known to cause P0725.
• Failing Shift Solenoid(s): You’ll likely see metal debris on the dipstick if this were the case.

Conclusion

While a bad input speed sensor is perhaps the most common cause of P0725 in the Toyota Prius, it’s one of many potential causes. Good luck fixing your vehicle.

P0193 is a generic OBD-II code that can occur in the Toyota Prius. It indicates that your Prius’s fuel rail pressure sensor is sending a signal to the PCM that is above its normal operating range (in terms of voltage value).

While P0193 is a generic code (it has the same meaning for any vehicle made for the 1996 model year and up), it can have different repair steps depending on what type of engine your Toyota has and the model year.

With P0193 there can only be two things going on with your Prius:

1. The fuel pressure reading is correct and abnormally high (likely a fuel pressure regulation issue).
2. The fuel pressure reading is incorrect (bad fuel pressure sensor, or wiring issue).

P0193 Symptoms: Toyota Prius

With P0193, there will likely be some observable symptoms.

Stalling

With too much fuel getting to your Prius’s fuel injectors or the PCM, the engine may stall out or hesitate in certain situations. There may also be a noticeable lack of power.

Air/Fuel Mixture Issues

Without a reliable reading from the fuel pressure sensor, your vehicle may end up with the wrong air/fuel mixture. If it runs too rich, you may get black smoke and P0172.

Unreliable Idle

P0193 can be caused when the fuel pressure regulator is bad. If the fuel pressure at the injectors is inconsistent, it’ll be really hard for your vehicle to maintain a steady idle speed. This can lead to the engine dying when coming to a stop as well.

Poor Fuel Mileage

Fuel mileage can suffer when the air/fuel mixture isn’t correct. You may also notice the stench of gas.

P0193 Causes: Toyota Prius

Here are the most common issues that cause P0193 to be thrown in the Toyota Prius:

Fuel Pressure Sensor

The fuel pressure sensor is responsible for telling your Prius’s ECM/PCM what the actual fuel pressure is. If it goes bad (or if the fuel pressure really is out of the normal range) P0193 can and will appear.

A bad fuel pressure sensor can force the vehicle to overwork the fuel pump, thinking that it’s constantly starving for fuel when it is not.

Wiring

Wiring issues can cause P0193 to be thrown. Take a look at the wiring harness around your Prius’s fuel pressure sensor. Does it look broken or damaged? Is the connection to the sensor solid? If it looks bad, it may need to be replaced.

Fuel Pressure Regulator

The fuel pressure regulator is responsible for making sure that the amount of fuel pressure that reaches the fuel rail is at a constant level (which will be less than pushed by the fuel pump). If your Prius’s fuel pressure regulator goes bad, it can restrict the flow of fuel to the point that P0193 can be thrown.

P0193 Diagnosis

A good scanner can help you look at the conditions that were present when the code was set. You can also use it to check the fuel pressure reading as you drive.

You’ll need to manually check your Prius’s fuel pressure if the reading seems off.

If the manual fuel pressure reading is normal, then you know that you’ve got an issue with the fuel pressure sensor (or the wiring going to and from it).  

If the fuel pressure reading is high, it’s likely the fuel pressure regulator causing P0193.

Conclusion

P0193 in the Toyota Prius can be a difficult code to track down, but should not be ignored. Doing so very well could leave your vehicle stranded. If there is anything that you would like to add, please leave a comment below. Good luck.

P0523 is a standard OBD2 trouble code that can occur in the Toyota Prius. In layman’s terms, it indicates the signal from the oil pressure sensor is higher than its normal operating range (in terms of voltage).

P0523 is generic (it has the same definition for all vehicles), repair steps will depend on your Prius’s model year and the engine equipped.

A bad oil pressure sensor is the most common cause of P0523. However, an oil system issue could trigger this code as well. Don’t assume the sensor is bad until you confirm the oil pressure manually. If there’s an oiling issue, it can cause engine damage or failure.

P0523 Definition: Engine Oil Pressure Sensor/Switch – High Input

Here’s precisely what P0523 is telling you:

Oil Pressure Sensor/Switch

The oil pressure sensor bolts into your Prius’s engine and relays the oil pressure reading to the Powertrain Control Module (PCM). It converts the mechanical pressure reading into a voltage value that the PCM understands.

From the PCM, the oil pressure is sent to the oil pressure gauge (or warning light).

High Input

The voltage value is almost at or above its highest possible value (which tells the PCM that the oil pressure level is very high). If the input was low, you’d have P0522.

Toyota Prius P0523 Symptoms

Your Prius may feel like it’s running and driving fine, but even without symptoms, you shouldn’t drive it with P0523 until you verify the oil pressure is fine.

Here are the most common symptoms associated with P0523:

• Check engine light
• High oil pressure reading on the gauge or the oil pressure light could be on

P0523 Toyota Prius Causes

Two things are going on. Either the oil pressure is too high, or there is an issue related to the oil pressure sensor.

Here are the most common causes of P0523 in the Toyota Prius and the proper order to check them.

Check the Oil

Verify that the oil level isn’t overly full. Is it sludgy? Is it the proper weight? If you didn’t pour it in yourself, it’s possible that the wrong viscosity was used the last time the oil was changed. Consider this possibility if you got P0523 right after an oil change.

Bad Oil Pressure Sensor – Wiring

If the oil level is correct, it’s not old, and it’s the proper viscosity, it’s time to look at your Prius’s oil pressure sensor. A wiring failure is widespread with these sensors due to their proximity to the exhaust.

Inspect the harness for any obvious damage. Look for cracked, broken, burnt, or brittle wiring. Follow the harness as long as you can, but pay particular attention to it within a couple of feet of where it plugs into the head.

Test the Oil Pressure Sensor

You can test the oil pressure switch/sensor with a simple multimeter. The video below will show you how to do it for just about every type of oil pressure sensor.

You could also get a mechanical oil pressure tester from a place like AutoZone or Harbor Freight. They’re usually around $25-$40 and will 100% tell you if you have a real oil pressure problem. That’s about the same price as a new oil pressure sensor, and you’ll be plugging into the same hole anyway.

If the manual oil pressure checks out, you have positive proof that your Prius doesn’t have a sensor or wiring issue.

Mechanical Issues

While a bad oil pressure sensor or wiring issue is the most common cause of P0523, it’s not the only one. If your Prius has a faulty oil pump or restricted oil passaged can also cause this code. You can verify this with an oil pressure test kit (it’s just a mechanical oil gauge with adapters to fit most makes/models).

Conclusion

While there are a few issues that can cause P0523 in they Toyota Prius, start by checking the oil and testing the oil pressure sensor. More often than not, that’ll fix the code. Good luck!

P0705 is a very common transmission-related trouble code that can occur in the Toyota Prius. In layman’s terms, it means that your Prius can’t tell what gear you’ve selected, which can have some real consequences on how it drives.

It’s most likely caused by a bad Transmission Range Sensor (TRS), but there are other causes that we’ll cover in the diagnosis section below.

P0705 Definition: TRS – Circuit Malfunction

Here’s the meaning of P0705, divided into its two main parts:

TRS

The Transmission Range Sensor (TRS) is responsible for telling your Prius’s Powertrain Control Module (PCM) or Transmission Control Module (TCM) what gear the vehicle is in. For this article, we will use PCM as the preferred term.

Perhaps the most common fix for P0705 is a new TRS. Usually, you’ll find the TRS bolted to the transmission, which makes it easy to find and replace. Unfortunately, on some Transmissions, it can be located on the inside, which makes replacing it at home nearly impossible.

Circuit Malfunction

A circuit malfunction means the TRS is not sending the proper signal to the PCM. There might be no signal at all, or the voltage value is not within the range of any gear. Either way, P0705 will be stored in the PCM’s memory, and the check engine light will come on.

Toyota Prius: P0705 Symptoms

The symptoms associated with P0705 in the Toyota Prius are going to vary depending on how the PCM reacts to not receiving a signal from the TRS (which can change depending on the model year and the equipped transmission).

Here are the most common symptoms:

• No start (the neutral safety switch doesn’t know what gear the transmission is in). See if it’ll start in neutral.
• Strange shift patterns (usually early shifts)
• Decreased MPG
• Delay between selecting a gear and transmission engagement
• No reverse lights

Toyota Prius: P0705 Causes + Diagnosis

If your Prius has an internal TRS, there’s not much you can do to troubleshoot it at home. On the other hand, if it’s external, here are some general steps you can follow.

You’ll need to find the shift linkage on the transmission.

Inspect the TRS

Inspect the TRS to see if there are any glaring problems. First, take a look at where the wiring harness plugs into it. Make sure that it’s still plugged in tight. Make sure there are no bent or pushed-out pins in the sensor.

If it’s plugged in tight and the pins look good, it’s time to move on to the wiring harness. Make sure that it is not burnt, cracked, shorted, or damaged. This is a common issue if your Toyota Prius has P0705.

If it starts in gear but not in neutral, the TRS could be out of alignment. There should be a neutral alignment mark on it.

TRS Replacement

Outside of a wiring or alignment issue, there’s not much else that can cause P0705 other than replacing the TRS.

Assuming the TRS is on the outside of the transmission on your Prius, replacing it is usually pretty straightforward. Some are more forgiving than others when it comes to aligning them; follow the directions and alignment marks, and you should be fine.

Conclusion

A bad TRS usually causes P0705. Where that TRS is located (in or on the transmission) is going to dictate whether or not you can do anything about it at home. Good luck fixing your Prius!

Daytime running lights (or DRL) are specialized lights that come on when your Toyota Prius’s regular headlights are turned off. Their purpose is to make it easier for other drivers to see you, theoretically decreasing the odds of getting into an accident.

If your Prius’s DRL warning light is on, the powertrain control module (commonly referred to as the PCM, your vehicle’s central computer) has detected an issue with the DRL system. A bad bulb is the most prevalent reason why the DRL warning light is on. Replacing it should remedy the problem.

Is it Safe to Drive with The DRL Warning Light On?

The daytime running light system is designed to help your Prius stay visible to drivers under various low light conditions, such as:

• Driving in and out of tunnels
• Fog
• Dawn and dusk
• Storms

It is perfectly safe to drive if your DRL warning light is on. However, if you are concerned about losing the slight gain in visibility generated by the daytime running lights, you can drive with your regular headlights on.

The DRL warning light is not a breakdown risk, and a Toyota Prius will still run and drive fine with it on.

Depending on the model year, some DRL systems are tied to the headlights, and you should make sure that the normal headlights are working correctly. You don’t want to discover that they aren’t when you’re driving at night.

Toyota Prius DRL Warning Light: Causes

There are two types of daytime running light systems. Since this is not a model year-specific guide, your Prius could have either version.

• Independent Bulb: Your Prius’s DRL system will have its own independent bulbs. This scenario is easier to test and diagnose.
• Headlight Integration: The system can be integrated into the headlights or parking lights (this is increasingly more common). Fire up your Prius’s headlights and see if all the bulbs are working. If one is burnt out, replace it.

If you are unsure which type of bulb your daytime running lights use, check the owner’s manual for the replacement bulb numbers. If the bulb numbers for the headlights are the same as the DRL lights, it’s likely that they are integrated.

Here are the most common causes that the DRL warning light might come on:

Bad Bulb (Most Common Reason)

A bad daytime running lightbulb/headlight is the most common reason the Toyota Prius’s DRL warning light comes on. Replacing it will likely turn the warning light off.

If your daytime running lights are on their own independent circuit, examine the bulbs. One of them should look noticeably burnt out. If they look good, take a look at the socket.

Bad Socket

Before running out and replacing the bulbs, pull one and make sure that the socket looks OK. If the socket is corroded or damaged, it’s likely the reason why the DRL warning light is on.

Often when a socket is bad, it can be hard to pull the bulb out. If this is the case with your scenario, wear some leather gloves, or get a thick rag to protect your hands from potential breakage.

If the socket is corroded or looks like it’s melted, you can splice a new one into the harness.

Other DRL Warning Light Causes

While a bad bulb or socket will cover the majority of the people reading this page, here are some of the other (less likely) causes that can cause the Prius’s DRL warning light to come on:

• Bad DRL Module
• Open or short in the wiring harness
• Blown fuse

Conclusion

The most common reason that the DRL warning light is on is a bad bulb. Most of the time, replacing it will fix the problem. Good luck fixing your Prius!