2010 Prius Hybrid Warning Light

Trouble code P0A94 is one of those listed in Safety recall campaign SSC-E0E and Warranty Enhancement Program– ZE3 as calling for replacement of internal component(s) of the inverter assembly. The specific internal component(s) to be replaced depend on the Detail Code that would accompany the main DTC.

Have you done recall E0E, where the Motor-Generator ECU and Power Management ECU are reprogrammed?
If you have not, then it is likely that there is a failure inside the Inverter.
Even if you had the ECUs reprogrammed, there is a chance for the to Inverter fail, even with the new programming, because it was already damaged, but not showing symptoms.

Warranty Enhancement Program– ZE3 covers the inverter for specific failures for 15 years from when the vehicle was first placed in service, with no mileage limit. P0A94 if one of these failures.

 

Its a tough call, who is correct about pump flow?
Helen had asked the tech to remove the cap and check the flow and the tech reported back that it was "OK".
The turbulence in a full reservoir is not extreme, as long as the car is in ready mode it will circulate. I find it easier to check for proper pump operation when the Prius is in the ready mode and the engine had shut down thus eliminating engine vibration.

 

Where are you seeing that Helen asked the tech to remove the cap and check flow. Are we reading the same thing? I see where she asked about flow and they said it was fine. Very likely because they don't know what they're looking for. If there is no movement of fluid thru the reservoir, there is no flow.

I agree that this needs to be done but if there is no flow, that needs to be addressed first.

 

I find the inverter coolant flow on my properly working Gen III isn't real obvious looking into the reservoir.
I had to pay really close attention to the fluid in my reservoir to notice the movement. (no bubbles, just slight movement)
I did find that with my Prius in ready mode with the engine shut down there is a noticeable vibration feel of the coolant flowing when clutching the lower reservoir hose.

Based on info provided by OP I am willing to make a friendly PayPal wager of $1.00 (only one person can take me up on this....after all I have to buy gasoline next month that the problem ends up being a failed inverter and not the pump (it would be a draw if it wasn't pump related or inverter related)

 

I'm not here to make wagers but I am here to try to help Helen and figure it out. Bubbles would indicate a problem (air in the system). I've seen the inverter pump problem several times and here are the symptoms.

* The car runs fine on short trips since the inverter doesn't get hot enough to trigger a problem
* On extended trips, the inverter heats up and goes into self protect mode and shuts down
* After it does this you have limited or no power
* If you pull over, shut it off, let the inverter cool of (about ten minutes), it will drive just fine again
* there is no flow of coolant thru the reservoir

The easiest way to check this is by looking for flow thru the reservoir. If there is no flow, it is the pump. I've never seen a dealer properly diagnose a bad inverter coolant pump by codes. There is no code for an bad pump. The only code you will get will be inverter related due to the shut down triggered by high temp.

 

The additive would not have caused your problem. I'm still betting on the inverter coolant pump replacement to finally solve this issue.

What is the longest trip that you had during the six weeks that it functioned normally?
Did you try to turn the car off for 10 minutes after the problem and restart?
How is the car running now? My guess is, it is running fine since the inverter cooled down.

 

Helen,
I can't state this confidently enough. You have a failed inverter coolant pump. If it is anything else, I will be completely surprised. All of your symptoms are exactly what will happen when your inverter coolant pump fails.

Do you have the car now?

 

No arguing with that.

Hang in there, keep updating, reading this with great interest.

 

Helen--> my sympathy. This is simply unacceptable and Toyota could lose a customer if they don't treat this issue seriously.

But what I would like to know is whether the three apparently heat-related failures of your inverter would increase the likelihood of future failures even if the underlying problem (say the inverter pump) were fixed.
My experience with personal computer solid state pieces such as CPUs that have heat-related failures was that the likelihood of failure became progressively worse the more times a failure had occurred. IF that principle is true for the Prius inverter, try to argue Toyota into replacing it even if they fix the underlying cause external to the inverter.
Good luck!

 

Helen,
There has never been any codes and there will not be any codes for this. That's why they have none now and they didn't have any before. The inverter coolant pump does not produce codes when it fails. These dealer technicians only know one thing, read the codes and fix what it tells you. They are baffled by a problem that doesn't produce codes.

Additionally, what Robert Holt said is true about allowing an inverter to overheat several times may cause premature failure in the future but I can just about guarantee you that they will not preemptively replace an inverter that's currently working. Additionally, they are very unlikely to replace it if it were to fail prematurely.

What you can tell the dealer to do to make the problem occur again is to have them drive the car for about a half hour and then take it up a large hill. This will cause the inverter to shut down again. I don't recommend they do this because this will cause another overheating event that may shorten the life of the inverter. What they really need to do is check for flow thru the inverter coolant reservoir when the car is turned on.

 

I got a similar story, with a brake related issue. Warning lights, but I was told I must bring it in while the dash is lit up, don't even turn it off.

Somewhere in the back of mind I think: this is progress? Also: are they bs'ing?

Supposedly codes are stored when the dash displays warnings, but they say that's not enough. I start to seriously wonder if they're just trying to deflect responsibility?

 

Helen, now that you have the car, did you pop the hood and look at the inverter coolant? While the car is READY (on) you should see turbulence in the reservoir. If you don't then you'll need to find a shop to replace the inverter coolant pump.

 

It is hard to rebuild trust in a car that has repeatedly failed.
My brother in law had a Mercedes that would suddenly shift in low gear and a "limp home mode" on the German Autobahns, a very dangerous occurrence. Same issue of,no codes posted as he had to turn it off and back on to get it to function normally, and the Mercedes dealers would not fix anything without the codes!! He never has purchased another Mercedes.
Good luck Helen!