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Auris Hybrid PLock Malfunction Error

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    Since last year, an error (PLock Malfunction), started to appear on the dashboard. After I stop the car and start it again only check hybrid system error remains (photos attached).

The error occurs in any conditions: car running/driving, car sitting with the engine running, car sitting with the engine stopped. I went to two Toyota dealerships and both said that they see communication errors and the problem is possible a loose connection (diagnostic reports attached). But like I said, this error occurs even when the car sits still with engine not running. I can't find a trigger for this. They wanted to remove the dashboard and check all the connections but, for me, this seems like a drastic measure.

The 12V batter was changed two years ago in summer 2018, the error started to appear in summer 2019. I'm writing this because I've found some, on other places, suggest that is the 12V Battery.

Do any of you encounter this problem or do you have any idea about what causes it ?? Thank you!

Auris Check Hybrid System.jpg

Auris Hybrid Diagnostic 1.png

Auris Hybrid Diagnostic 2.png

Auris Hybrid PLock Malfunction.jpg

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Whilst you are waiting for some more replies, it might be worth me putting my interpretation on your fault.

I have not heard of this problem in normal use on an Auris, I don't remember anyone reporting it before.

It appears you have researched this problem already, so most of the following is probably already known to you:-

On almost all modern cars, all the major computers (ABS, Vehicle Stability Control, Engine ECU etc.) communicate with each other via a CAN bus (https://en.wikipedia.org/wiki/CAN_bus#:~:text=A Controller Area Network (CAN,applications without a host computer.)  This simplifies manufacture, and the wiring loom is reduced in complexity.

The errors you are getting suggest that that this 'data highway' is intermittently not functioning.  The problem could be due to a simple bad connection, or a poor grounding/earthing to the vehicle chassis.  In the first instance, it is probably worth thoroughly cleaning/wire brushing/re-tightening all the earthing points, especially around the engine bay.  This is especially important if the car is in salty, harsh environment e.g. northern European countries, or living near the sea.

The dealership's suggestion sounds reasonable, but checking all the earthing (including the Battery connection at both ends) would be an economical first step and something you could possibly do yourself.  Has the car suffered any water leaks or had any accident damage?  Is the engine under-bonnet area corroded much?  Has there been any modification the the cars electrical system for new accessories, dash cameras or radios etc.?

I have caused a vaguely similar problem, just once, in very specific circumstances, when I disconnected and reconnected a diagnostic tool into the car's diagnostic socket (OBD2 socket) whilst the car was in motion, this seemed to 'panic the bus' and caused a major, fleeting reset to the CAN bus.  It has never happened since.  There were not quite as many errors as you have had, but they were of similar nature.  I put that problem down to my 'operator error' - don't plug anything into the car's CAN bus whilst it is moving - not that that is what you are doing, of course.

Best of luck!


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Might be worth checking Prius discussion forums, given it's the same drivetrain.

The computer engineer in me thinks it's plausible that it's a dodgy connection. Damaged wire or bad connection somewhere, likely not easy to trace. ☹️

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It looks like something is taking down the canbus, I would suspect water ingress into a connector on a module somewhere or a module going bad

Power and grounds would be a good place to start, was the Battery replaced with the correct type (AGM) and not a lead acid type ? ? As the charging systems are very different

what is the model number of the Battery ? picture ?

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@Greg The car has not been sitting in a salty environment but water/connector oxidation could be the cause.

@flash22 The Battery was replaced at the dealership with an original one. And last time I was at a dealership (different one) I told them specifically to check the Battery and they said that is not that.

I made an appointment at the dealership to run a diagnosis again and I'll see what I'm going to do after that. The "funny" thing is that in 3 out of 4 cases the error disappeared when I arrived there. Is like it knows 😀

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I would think the can bus will need to be scoped and monitored, then the system broken down into segments to pinpoint the cause, it will only take one module to take down the bus


without seeing wiring diagrams it difficult to what is on the bus or layout of the bus

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  • 2 weeks later...

Two things:

1. I noticed something strange today: after I filled up the gas tank the error disappeared. In the last two weeks the error kept appearing; the tank was a quarter full (I made only 4 - 5 small drives <about 5km each>).

But today I made a longer trip 200km and I needed to refill the tank. After I refilled the tank the error "Check hybrid system" disappeared and the error "pLock malfunction" never appeared in the 3 hour drive (busy road).

In the previous months I never checked how much gas was in the tank when the error occurred, but honestly I don't know if this is just a coincidence or not.

Do you know if a sensor or something else influenced by the gas level in the tank could cause this error ?

2. About two years ago I had to carry something heavier in the trunk, about 20 - 25 kg, and the error "check hybrid system" appeared on the dashboard. After I repositioned the load the error disappeared. The package was placed over the hybrid Battery.

Do you think a faulty connection at the hybrid Battery could cause the error ?

In 4 days I'll go again to the dealership for a more thorough  investigation.

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