RX 450h 2010 Check hybrid system error (code P0A7A-122)

[Peter Popov]

This is a bit of a long story but I'll try to make it as short as possible.

I started getting this P0A7A-122 code - generator inverter fail signal detection (overcurrent due to system malfunction) - about a year ago. Took it to an authorized service and was told to replace the HV inverter-converter and if that doesn't work, replace the transaxle assembly next. The parts alone cost more than I paid for the car (got it used in 2020) so that was definitely a no-no. I've been living with this error with no issues for over a year with no issues, and it would disappear after a while (from the dashboard, not from memory.) Then one day, I got it again, and then "Check AWD" and "Check braking system" followed in a matter of seconds. The vehicle then basically shut down to EV - barely had enough time to pull over. I turned it off and on again and it lit up, but that's when I decided to take her to an independent mechanic. They took apart all the power cabling, cleaned up all contacts and applied contact spray, checked both MGs for shorts, and checked the inverter triacs (are they triacs?) It didn't help. I then found an identical vehicle scrapped for parts and replaced the HV inverter-converter, the HV ECM, and MG2 (thinking it was the only connection between the HV, AWD and braking systems.) That didn't help either.

The last few times that it happened, I finally noticed a pattern. The car would "stall" for a split second, not hard enough to engage the seatbelt but definitely causing me to noticeably lurch forward, and then the error would immediately follow. The last time it happened, I managed to pull the freeze frame data from it (see attached Excel file.) A few things I've highlighted in the freeze frame data:

1. Accelerator position is constant. I was driving at around 15 mph (25 km/h) and was not accelerating
2. Engine RPM drops from 1280 to 32 within two seconds. This is the stall I felt
3. Manifold Air Pressure drops from 67 to 18 in the same period
4. Manifold Air Pressure is significantly different from atmospheric pressure. Is this normal? I'm at less than a thousand feet above sea level.
5. Engine rev (real and target) drop to zero right before the error occurs, which makes sense (I think) given the stall, but I don't know if the difference between the two values is indicative of anything.
6. Power resource IB is all over the place, going from -18V to +12V in just a second. Is this expected?
7. MG1 carrier frequency drops to 3.5 kHz for a second, right before the error code is triggered
8. Calculate Load, Throttle Position, and Generate Torque all trend down throughout the freeze frame. Is this expected given the car "stalled"?

Any ideas? Having ruled out the inverter-converter and hybrid control modules, I find myself obsessing over the MAP value. I don't know much about cars so this could be complete nonsense, but I'm thinking - if there's an issue with airflow or the sensor causing the air-fuel mixture to momentarily and unexpectedly stall the ICE, wouldn't that result in MG1 suddenly turning all the excess braking torque in an abnormally high current that the ECM doesn't expect to see? I'm basically grasping for straws here so any help will be much appreciated!

Thanks,

Peter

Freeze frame data.xlsx

[RX400h]

How old is the 12V battery? Sometimes a failing 12V battery will cause very weird things to happen. One time I saw a code that made me initially think that a big repair was coming up. I checked the 12V battery and one cell was low, so I added distilled water. The message was reset by the dealership and the message never returned. That was 3-4 years ago.

[Peter Popov]

Forgot to mention as I didn't think it was related. Had that changed too, just a week ago - before this last episode. This last code is fresh, one day after the new 12V battery. I put an AGM this time, hopefully it will be alright on that front at least.

[RX400h]

One thing I've learned over the years is that like medical specialists, auto mechanics are not equal to each other in their troubleshooting abilities. Perhaps there is a mechanic at a different dealership who has more experience with the symptoms your vehicle has. 

[Peter Popov]

Agreed. This particular car is in my hometown back in Europe (hence the SI units) and there aren't many shops that would take on a hybrid there. I've tried the official Toyota dealership as well as the only officially authorized third party shop in a hundred-mile radius.

A couple of corrections/additions to my original post (can't find a way to edit it):

1. I did not replace MG2, I replaced the rear motor (d'oh!)
2. I double-checked and accelerator position is not constant. Looks like I lifted my foot for a second and then tried to accelerate when it stalled
3. From what I've found out, it looks like freeze frame data is recorded every half second, not every second as I thought initially

Am I on the right track to be thinking about either the MAP sensor itself or the actual air intake?

[RX400h]

There are some websites that allow you to pose your question and get it answered by an auto technician who specializes in your brand of vehicle. They may charge a fee but I think it may be worth checking out. The average independent shop mechanic is unlikely to solve this quandary.

[Alexset]

@Peter Popov, were you able to figure out the issue? I have 2011 RX450h with exactly the same behaviour. Bought it recently, and the error P0A7A code was thrown after a week or so. Just ordered mini VCI tool to diagnose it better.

 

Edited November 14, 2023 by Alexset

[Ron Dobson]

I have a 2011 with the same problem, had it diagnosed and was told that I needed a new generator inverter ( 6k ) good luck finding a used one