You know the feeling when your Prius displays the “P Lock Malfunction” message and fails to start. Like other warning notifications, the Prius P lock malfunction signifies several problems with your vehicle. This issue will lock your car in the Park position and leave you stranded.
So, what does this warning notification mean, and what can you do about it? I discuss the P lock malfunction Prius, its possible causes, and how to solve each issue.
Question: What Does the P Lock Malfunction Mean?
The P lock malfunction is an alert on your Prius’ dashboard to indicate your car has been locked in the Park (P) position. That means you can’t shift the vehicle out of Park.
Vehicles with the 12V auxiliary battery have a P lock as a central lock option. The P lock prevents your car from shifting out of the Park mode without pressing the brake pedal. However, several issues can cause the P lock to misbehave and prevent the vehicle from shifting out of the Park.
The P lock malfunction message appears when the onboard computer detects a problem with the vehicle, causing the gear to fail. Below is how the P lock malfunction Prius occurs on the dash:
“P Lock Malfunction. When Parking, Park in Flat Place and Apply Parking Brake Securely.”
This message indicates your Prius has underlying problems preventing shifting from Park to Gear, Reverse, or Neutral.
Answer: Causes of Prius P Lock Malfunction and Fixes
The leading causes of the P lock malfunction are battery and fuse failure. Let’s discuss these causes and more to ensure your Prius is up and running.
Battery Failure
Your Prius relies on the auxiliary battery to power all the components involved in the startup process. If the battery is okay, it allows the components to work correctly and ensures the engine turns on smoothly. But like any other battery, the Prius auxiliary battery can experience some problems and malfunction.
You will likely see the P lock malfunction message if you have an auxiliary battery that doesn’t power the vehicle during startup.
Some owners claim that their Prius may start, and the message disappears after driving for a while. If that happens with your car, the possible cause is a drained battery. Before charging the battery, you must consider the cause of the battery draining faster than expected.
Leaving the lights or radio on overnight will drain the battery faster. Check the root cause and fix it. Then, charge the battery in your garage. Alternatively, use a portable jump starter to start the engine and allow the battery to charge.
Many Prius owners have reported that the P lock malfunction message usually appears when it’s raining. If that’s the case with your car, check for water or moisture accumulation in the battery compartment. You can wipe the water on the battery using a rag or towel.
While still on the battery, check for corrosion on the terminals and loose terminal cables. Your Prius will display the error message if the battery has such issues. Clean the corroded terminals to ensure uninterrupted flow of electrical power. Then, ensure the cable connections are secure.
If the P lock malfunction Prius notification persists, test if the battery is faulty. A digital multimeter will help perform the test and know if the battery needs replacing. You may want to visit a professional mechanic to examine and replace the auxiliary battery.
Blown Fuse
Your Prius has several fuses that control electrical power flow to various electrical components. One of these fuses controls the parking system, inverter, and converter. Issues such as a short circuit, overloaded circuit, and damaged wiring can cause this fuse to blow out.
A blown fuse prevents current from flowing to the vehicle’s parking system. If your Prius is in Park, you’ll receive the “P Lock Malfunction” message on the dash. That means there’s no power to help shift your car out of the Park mode.
The best way to resolve this problem is to replace the blown fuse. Locate this fuse in the fuse box and examine it. Your Prius user’s manual will help you locate this fuse in the box. Use a fuse puller to remove a blown or melted fuse. Then, install a new fuse with a rating identical to the previous one.
Remember that replacing the fuse without fixing the cause of a blown fuse won’t help. The fuse will likely blow out again and cause the error message to appear on the dash. So, inspect your car for any issues causing the fuse to blow out and resolve them.
Damaged Wiring Harness
The transmission system in your Prius relies on a wiring harness to allow communication with the ECU. If the wiring is in good condition, there will be proper communication between the TCU and the ECU. This communication allows you to shift from Park to Drive, Reverse, or Neutral.
Unfortunately, rodents, bumpy rides, or overheating issues can cause the wiring harness to get damaged. When this happens, the ECU and TCU won’t communicate. This issue may result in the Prius P lock malfunction notification appearing on the dash.
Locate the wiring harness with the help of your manual and inspect it for signs of damage. You can also check the connectors and clean or tighten them appropriately. Replace the wiring harness if it appears damaged.
Faulty ECU
A faulty Engine Control Unit could also be to blame if your Prius has the “P Park Malfunction” message. If the ECU is defective, it won’t communicate with the TCU to allow the shifting process to work as expected.
A faulty ECU will show symptoms like no ignition, check engine light, engine surge, misfiring, stalling, and failing electrical components. Note that these symptoms are also indicative of other issues in your car. So, use an OBD-II scanner to look for error codes for a failing ECU.
Clearing the error codes with your scanner can be a temporary P lock malfunction fix. The method will delete any codes causing the ECU to malfunction. Unfortunately, it won’t fix the underlying problems.
Alternatively, try resetting the ECU to see if the vehicle will shift out of the Park mode. Here are steps for resetting your Prius ECU.
- Locate the battery in the hood and turn off your Prius.
- Disconnect the battery’s negative terminal.
- Wait for about 15-20 minutes. Doing this drains all the electricity in the components.
- Reconnect the negative terminal.
- Start your Prius and check if it shifts from Park.
If resetting the ECU doesn’t work, let your professional diagnose and fix the root problem. The professional may upgrade or replace the ECU if necessary.
Answer: Temporary P Lock Malfunction Prius Fix
You can use the following temporary fixes to address the P lock malfunction Prius.
- Pressing the brake pedal: Step on the brake pedal hard and turn on the ignition. When the engine starts, try shifting out of Park. If this fails, wait 2-3 minutes and repeat the process.
- Pressing the power button twice: Locate the power button and press it twice. When doing this, you must ensure the key fob is in your Prius.
If the above fixes fail, tow your Prius to a repair shop or call a mobile mechanic to come and fix your car.
Final Thoughts
Several issues can trigger the Prius P lock malfunction message on the dash. If you see this error notification, check the auxiliary battery and the fuse for defects. Other possible causes of this problem are a faulty ECU and a damaged wiring harness.
Troubleshoot the underlying cause to get your Prius back on the road. If you can’t address the root problem, call a professional mechanic for help.