Prius P Lock Malfunction: Reasons, Fixes, And Many More!

Prius P lock malfunction can occur for 3 reasons. Firstly, a drained car battery can cause a malfunction in the p lock. Secondly, a faulty 12-volt battery can be the reason. Finally, blown fuses in the fuse box of the car can also hinder functionality. However, all of these issues are fixable.

P lock is a really useful feature of cars. This system has also been implemented in the Toyota Prius for a long time. However, users have been facing some problems with the P lock recently. In these situations, the Prius doesn’t start due to the p lock fault.

So, what is the issue with the prius p lock malfunction?

This is only a quick review of the article. To deal with the malfunction fully, you’ll need to know more. Keep reading the article till the end!

What Is The P Lock of Prius?

The p lock system of Prius exists since 2012. P lock in a Prius stands for ‘parking lock’. This refers to the parking lock system for certain vehicles with 12V batteries. Not all vehicles contain the parking lock feature.

The P lock is put to work when the gear of the Prius is shifted to ‘P’ that is parking. After that, whenever the car needs to be put on ‘D’ that is driving, the lock is released. This system can also be used as a car alarm system. It can detect when a Prius is fully parked.


P lock is a special locking feature of cars, which refers to ‘parking lock’. This lock activates when a vehicle is parked and can malfunction.

What Causes A Prius P Lock Malfunction?

The reasons behind the Prius P lock revolve around the auxiliary battery, weather, fuse, etc. I have elaborated on the reasons below. Have a good read.

Reason 1: Battery Problems

The Prius p lock malfunction can easily occur due to a drained battery. Whether it’s accidental or deliberate, a drained battery blocks the functionality of a p lock.

A car battery can be drained for many reasons. However, there are some common issues that can drain the car’s battery. These include headlight/AC turned on while the engine isn’t running, open doors, etc.

Furthermore, a faulty or loosely connected 12-volt battery is another reason why the locking system fails in a car. It’s also responsible for some other functionalities including the p lock.

Solution 1 of 1: Recharge or Replace the Battery

Before replacing the car battery/auxiliary battery, you need to test it for drainage. You can confirm a drained battery by testing it with a multimeter. 

Get a multimeter and connect it to the terminals of your car battery. Set the multimeter volt range above 15V or 20V. Note down the multimeter readings. (1) 

From there, you can match the readings to this table here-

Multimeter ReadingsBattery ConditionAction Needed
12.4 volts or aboveGood and fully chargedNo action needed. Move on to the next fix.
Below 11.9 VoltsBattery is dischargedRecharge the battery
Below 10.5 voltsBattery is deadReplace the battery

A healthy and fully charged battery should give out readings of 12.4 – 12.6 volts or above.

If the reading’s going below 10.5 volts, the battery might have dead cells. In this case, a full replacement of the battery is needed. 

If your battery is completely discharged, it should give out a reading of 11.9 volts.  In such a case, you have to recharge the battery to its maximum capacity. You may use a trickle charger to recharge the Prius battery.

Connect the clips of the charger with the terminals of the battery. Connect the black wire with the black terminal and the red wire with the red terminal.

This way, you can identify and solve battery-related problems by the readings of the car battery. By doing so, you can get rid of the p lock malfunction.

Solution 2 of 2: Disconnect & Reconnect The Battery

Disconnecting and reconnecting the battery is a quick fix to dodge the malfunctioning p lock. Whenever you see the p lock malfunctioning lights, you can disconnect the battery of the car.

To disconnect the Prius battery, first, turn the Prius off. Put on a pair of some Rubber insulated electrical safety gloves so you can avoid getting electrocuted.

After that, disconnect the primary cables that are currently attached to the battery. The black cables are negative whilst the red cables are positive. Disconnect the black cables from the negative terminals first.

After that, disconnect the red cables. These cables should be connected to the positive terminal. Consult the owner’s manual if you’re confused about anything. 

Be careful not to touch any metal surfaces of the terminals of the battery. Any electricity transfer between the terminals may cause accidents. 

Wait a few minutes after disconnecting the battery from your Prius. Then reconnect the battery. Start in the reverse order; first, connect the positive terminals. After that, connect the negative terminals. Finally, start your Prius.

You may observe a few distinct battery warning lights. Don’t worry about them as they appear for the sudden removal of the battery. Restarting the car may get rid of them. The P lock malfunction notification, however, should be gone in the first ignition. (2)

Reason 2: Blown Fuse

Fuses are quite essential parts of a car. This small component protects all the breakers and electrical functionalities of a car. If a fuse is blown, the associated functionality will not work. 

The p locks in a Prius are also protected by a fuse. All the necessary fuses of the car reside in the fuse box.

On the fuse box cover, all the fuses and the features they’re related to are listed. Chances are, the fuse protecting the p lock feature is blown. 

If that is the case, it can cause malfunctioning. 

Solution: Replace The Blown Fuse

If you find a fuse of your Prius in a burnt or damaged state, chances are it’s blown. But hey, you don’t have to worry. All you need to do is replace the blown fuses and you’re good to go.

To locate the blown fuse, you need to use a digital ohm meter. Set the meter to ‘ohm’ mode. Then, touch the 2 ends of the digital ohm meter with the pins of the fuse. If the resistance of the fuse does not match the reading, it’s blown. 

If the fuse is transparent, you can also look at the circuit inside it. If there’s a short circuit (disconnected wires) then the fuse is blown. In such cases, it needs a replacement.

While replacing the blown fuse, ensure the replacement fuse’s amp rating and size factor. It should be identical to the original one as it won’t fit otherwise. 

Reason 3: Damaged Wiring Harness

The P lock of the Prius functions electronically. So, if the wiring harness is damaged, electricity flow will be hampered. Hence, it could cause the P lock to malfunction.

Solution: Fix or Replace The Wiring Harness

If the wiring harness is damaged, don’t worry. It is totally fixable by a bit of insulation. Follow the steps below to fix the wiring harness of your Prius-

  1. First, get a plier. Trim the damaged portions of the wire. After trimming, there should be two wire ends that are open-ended.
  2. Then, cut a replacement wire to connect the previous wires. This wire will act as a linker for the open ends.
  3. After that, strip the ends of the wire. After stripping, the copper cables should be out by 1-2 centimeters.. 
  4. Next, put a heat shrink tube on the strip. Slide it through one end. 
  5. Then, take the ends of the wire and fray them. The intertwined wires will restore the connection.
  6. Finally, use a heat gun and heal the connection with the heat shrink tube on top. If you wish, you can use multiple heat shrink tubes, depending on the length.

Sometimes, the wire harness experiences irreversible damage and can’t be fixed. In that case, you can replace it.

Reason 4: Defective ECU

One of the most crucial components in a car is the Engine Control Unit (ECU). This electrical component regulates and monitors other electrical components. 

However, if the ECU stops working, the transmission system and other components lose connection. This can ultimately lead to the p lock malfunction.

Solution: Reset or Replace The ECU

In many cases, a bad ECU unit causes malfunctions. Some common symptoms can be observed when an ECU goes bad. For instance, the Prius engine will start stalling and misfiring. Sometimes the engine surge and ignition might be absent.

A bad ECU can actively cause the electrical components not to work. For that, your p lock may malfunction as well. But it can be solved. 

Generally, an ECU reset may fix the problem. Simply disconnecting and connecting the car battery resets the ECU. Alternatively, you can unplug and plug the ECU fuse to do this.

If the ECU reset does not work, it may need to be replaced. A complete replacement of the ECU can fix the issue, but it’s costly also. So if you’re in this situation, consulting a car mechanic/technician will be the best advice. 


The malfunctioning of a Prius p lock can occur for 4 different reasons. Drained car batteries or a faulty 12-volt battery may cause it. Any blown fuses inside the fuse box or the wiring harness can be a reason. Faulty ECUs may trigger it too. All of these can be solved by repairing/replacing.

Fixing The P Lock Malfunction: What Else Can You Try?

If the above solution doesn’t fix the issue, you can try the following-

Pump The Brake Pedal

Pumping the brake pedal of your Prius sometimes makes the p lock function properly. It creates momentum to the pedal break which helps the P lock system break free.

This method is the go-to fix when the temperature is cold outside. Sometimes the weather may jam the break and activate the p lock. In that case, this is the solution. 

To start off, start your car. While the p lock is malfunctioning, the engine may not start up to the rev range. But you don’t need that either. Just let the dashboard illuminate and you’ll be good to go.

After that, repeatedly press the brake and depress the brake. Apply firm pressure while doing this. After a few pumps, restart the ignition. Keep doing these steps until the Prius starts and reaches its rev range. You should hear the engine’s sound if it succeeds. 


If the traditional fixes aren’t working, you can try pumping the brake pedal. This is a non-conventional solution that can remove the jamming of gears. As a result, the p lock malfunction may be fixed.
Prius P Lock Malfunction Infographic


Does The Prius Have Automatic Parking?

Yes, Prius does have an automatic parking feature. To get started with auto parking a Prius, find the ParkAssist button near the dashboard. It should be on the driver’s side. Pressing the button will put up a screen on the dashboard, letting you select the spot. Select and park!

What Can Cause a Hybrid System to Malfunction?

Hybrid systems can malfunction because of overheating, blown fuses, electrical problems, etc. These factors basically stop the system from working optimally. Additionally, the electric motors of hybrid vehicles stop working properly. Then, only the combustion part of the hybrid vehicle is functional.

Why Is My Prius Not Locking Properly?

Prius may not lock properly because of the key FOB battery. If the FOB battery is dead, the keyless entry will not work. This happens because the communication between the key and the central locking system gets interrupted. Don’t stress though. The key FOB battery can be easily swapped.

Final Verdict

From the discussion above, now you should know why the prius p lock malfunction occurs. The good news is, you can fix it! 

Rather than waiting for a problem, you should regularly test the peripherals of the car. It is the safest option; it can also save you tons of money!

Have a great day.

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William Baldwin

This Is William Baldwin, The Founder & Managing Editor of this website. Me and my team share automotive tips, tricks, and news

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Talha Atta

Talha Atta, a Mechanical Engineer and experienced technical content writer and editor at with a passion for the automotive industry.