Help with fault code and noise p0a78

[Sean84]

Hello people I wonder if anyone has any advice from experience. 

I have gs450h, brand new Battery fitted. Both 12 and hv. Occasionally i get fault code P0A78. I know when this fault is likely to happen too. It's strange, sometimes when I pull off and it stays in electric mode, the electric motor seems to create a much louder electric whine than normal. It's a sound a bit like a loud milk float from years ago, a bit like a regen sound, a little bit like a engine car in reverse sound. It only does this sometimes, and when it does I expect the dash to light up with all the usual hybrid warnings and give code P0A78. I understand this is generally an inverter code. However i find the nose produced from the gearbox /electric motor rather odd and it's not just a coincidence. 

Also sometimes if I accelerate from a standstill so it engages electric motor and demands a lot of torque and starting engine at same time it will judder like it's stalled and repeatedly in quick secession try again and stall until I lift the pedal a little, then it will drive as normal even with warnings up on dash. 

Is this a power supply problem noise from a bad inverter? Or is it likely a problem in the gearbox with the motors? Any familiar experience with anyone? 

Thanks for taking the time to read 

[Mr Vlad]

Hi Sean. You say you had both 12v and High Voltage batteries changed. Where did you have this done?

Why did you have to have this done?

How many miles are on your car?

[Sean84]

Hello Mr Vlad. New 12v from lexus, brand new high voltage is a lexus Toyota one fitted by the hybrid repair service. Car has done 64k miles. Majority of the time it's p0a78. Especially on start up at a stand still. Sometimes on pulling up to a stand still it feels like the engine and transmission do not disengage properly and forced the engine to stall. Occasionally gets P0a90. 

The noise prior to getting a code sounds like hybrid electric, but louder at a different frequency, and braking gives a much heavier brake regen noise and feeling. I'm starting to think inverter. But I'm also keen to start with a simple atf change. I'm waiting on a techstream to see if I can try any commands in the box like b1 and b2. And read individual phase readings if possible. I have never used techstream but I'm familiar with other manufacturers diagnostics kit. I'm hoping an inverter change will fix the problem. Perhaps it appears to be transmission problems because of bad commands from the inverter which i believe is also the main brain for the whole transmission. I also read somewhere that there is a command to' bleed b1 or b2'. I understand this transmission on a deep level after learning from much information about the L110 transmission. Any ideas would be appreciated. I'm preparing to do pretty much anything other than a transmission swap as i believe that involves dropping the whole lot with the engine before separating 

[ColinBarber]

There should be sub-code(s) for P0A78 to help narrow down the problem further but it is generically inverter/motor related - possibly HV cables. I'd check all the HV cable connections are clean and tight on the motor, inverter and Battery (with the usual HV warning - please don't attempt this if you aren't comfortable working with HV DC or don't know how to isolate the battery/discharge the inverter).

[Sean84]

Thank you Colin. Those sub codes are exactly what I seek, that's why I'm waiting a techstream. I am most comfortable working on any electrics, it's my main thing. That's why I specifically bought a hybrid because i believe that any electricity problems i will be able to get to the bottom of. It's easier if I have help on forums like this. But regardless, I will get to the bottom of it. Appricate your advice 

[Sean84]

This video just about picks up the sounds. Unfortunately my keys between my legs kept jingling every now and then. Right at the end it's very clear. It's so intermittent and i can't make it happen. It just sometimes happens. 

Since the high voltage Battery change the car has been much more improved and reliable. But this separate intermittent problem i need answer to. Still waiting on my techstream in the post 

[Mr Vlad]

This may sound daft but. Since you've had new batteries etc maybe the motors are getting more juice than they used to and are working with a more pronounced whir. 

I'm no electrical engineer but my common sense is kicking in. I seen to recall I had a similar whir with my beloved RX450H I had a few years back. (I miss that car). 

But also possible that when all that HV work was done that a connection or two may be just a little loose or dirty. Just reiterating what Colin suggested. 

[Sean84]

Mr Vlad, i don't believe you're theory stands for two reasons, one, this was also happening before Battery change. And two, 95% of the time it is fine, it is happening intermittently and at random times. Often when this happens, as I brake to a stand still, it feels like there's some kind of friction resistance. When the noise is extra loud whirring i can even feel it through the gear selector. It's most odd. All i can do for now is wait my device to read any deeper codes 

[Sean84]

I've also noticed that when this noise is happening, I'm getting a lot of regen 'E' on the mpg counter. It's almost as if the regen brake is sticking somehow even when giving power. This just doesn't make sense. I always see a lot of small 'E' on the screen when this is happening. And it's hard to explain, but it's just different to normal regen where i may coast down hill or brake fairly hard for a distance. 

 

I know what the E means on the screen. It's just seems more when this problem occurs. As if one of the clutch brakes aren't working properly. 

 

[Sean84]

I've also noticed, when I try to pull off really slow with no accelerator, just releasing the brake slightly, still pressing slightly , it crawled forward but not smoothly, it's jerky. Like a phase is down. I hope this techstream turns up tomorrow. 

I'll do a video shortly see if anyone make sense of it 

17 hours ago, Sean84 said:

I've also noticed that when this noise is happening, I'm getting a lot of regen 'E' on the mpg counter. It's almost as if the regen brake is sticking somehow even when giving power. This just doesn't make sense. I always see a lot of small 'E' on the screen when this is happening. And it's hard to explain, but it's just different to normal regen where i may coast down hill or brake fairly hard for a distance. 

 

I know what the E means on the screen. It's just seems more when this problem occurs. As if one of the clutch brakes aren't working properly. 

 

[ColinBarber]

27 minutes ago, Sean84 said:

Like a phase is down. I hope this techstream turns up tomorrow. 

Possible, but there are current sensors on the individual phases which should throw up a different error to P0a78 if that were the case.

[Sean84]

14 minutes ago, ColinBarber said:

Possible, but there are current sensors on the individual phases which should throw up a different error to P0a78 if that were the case.

That's what I would expect also. It just doesn't make any sense. It's so intermittent though I'm really hoping it's electrical problem, inverter at worst. The only thing I don't want to be doing is changing the transmission. I'll get a video of the sound on the next chance. It's really thrown me. I know mechanical workings very well, and I understand electronics very well. As a part time hobby I do pcb repair. I know how to diagnose bad pcb parts and replace them. That's why I want to get to the bottom of this problem. I don't like being defeated by anything like this 

[steve2006]

You really do need those Techstream sub codes as Colin mentioned.

[Sean84]

1 hour ago, steve2006 said:

You really do need those Techstream sub codes as Colin mentioned.

Yes mate, I'm already on it, waiting delivery. I wad kind of hoping it might already sound familiar to anyone. Right now I believe maybe inverter. It's intermittent, and mostly not a problem. In my experience, it appears to be an electronic fault from pcb, like a relay or transistor, which in turn does or doesn't actuate something mechanical, so appears to be a mechanical fault. I'll be back when I have codes or any other symptoms to explain. Thanks to anyone on this topic 

[steve2006]

The demise of leaded solder created a lot of problems with poor solder joints, chances are dry joints on the inverter PCB. If you have some MIL spec solder I.e. leaded get the soldering station out 😀

[Mr Vlad]

Now that problem is huge in the mk2 ford focus. Dry joints in the circuit board in the dash. 

[Sean84]

On 7/18/2024 at 7:13 PM, steve2006 said:

The demise of leaded solder created a lot of problems with poor solder joints, chances are dry joints on the inverter PCB. If you have some MIL spec solder I.e. leaded get the soldering station out 😀

Awsome, i had this as one of my first theories with my friend who works for Renault and is EV trained. At the end of the day it's a 15 year old board and stored in the engine bay of a car. 

Next question before I go looking, is this board accessible and removable without removing the whole inverter unit? I have no issues doing the electric work, I don't feel like doing all the other work involved, draining coolant etc then refilling and bleeding after if I can avoid all that 

[Sean84]

So, one more key strange occurrence I've noticed when the problem happens.... I have Dr. Prius app running and see a fair bit on the power side, when I brake hard while the odd noise is happening, I notice that the voltage goes just above 360v and into red numbers, as high as 384v, doesn't matter if Battery is saying 40% or 60% it only goes so high when this regen sounding noise is extra loud. I don't always get a fault code. 

Also when I try move slow it's clunky and judder in forward or reverse and if I go to slow, for instance up hill with out enough power it will basically stall and throw hybrid check even though it's in ev mode 

[Sean84]

Here's a video of the regen brake voltage on screen. Only on the intermittent fault. It's not normally like this . Doesn't normally go that high. Only when this noise is present. I was really hoping all this would sound like someone gas already experienced and would already have answers. I will get to the bottom of this 

 

 

[Mr Vlad]

You seem to be going thru the mill with this issue. It's good you're electrically knowledgeable. Have you asked the place where you got the Battery swap their opinion? Have you asked a lexus dealer for an opinion? 

Something has come to mind. I've personally experienced that changing a Battery in a laptop can throw up all kinds of krap. A Battery that's none standard caused issues. When I got an OE Battery then no issues. Just an observation but true. Maybe the new HV Battery isn't actually performing right. Dodgy to put it bluntly. It can happen. 

[Sean84]

Hi again Mr Vlad. Thanks again for your input. What you say totally can be the case with many electronic items. However, in this instance it 'should not' be my issue. Both battery's are manufacturer specific. And any problems I had when I first got the car have massively improved, ie, Battery capacity. Before, the voltage was always dropping into red when amp draw is high, starting engine or accelerate hard, even when charge was high. This problem has improved. But this blimming intermittent problem is annoying. One day it'll drive fine for 200 miles 

Another day it'll spend the whole day sounding like it's running with electric fault and throwing codes. 

I noticed today that while driving the motorway while it sounds bad it was charging at a high amp rate compared to normal,. Voltage stayed in safe zone though. It really feels like a electronic magnet brake is always on. I just don't understand it fully yet. 

My techstream was hoped to arrive today but maybe Monday by looks of it. 

I haven't spoken to a lexus mechanic because i don't know any to speak to, but i know other manufacturer mechanics and the trouble is i imagine lexus will be just like other manufacturer workshops, and instead of spending lots of time to find the actual problem and fix it they generally swap out a while part, instead of a component of a part. And the cost going through a main dealer makes it inefficient really. Plus the fact, anyone can take a car back to its manufacture for repair. I try and do everything myself, with help if necessary. 

For me, as annoying as it is, i enjoy the challenge 

I could just get rid of car and get new one but my life, my work, everything I do is about fixing things. I don't give up easy 🙂

[Sean84]

Here's a little example of the noise when at crawl.

95% of the time it's smooth like a normal ev. But when this intermittent fault occurs it sounds like this. The noise isn't the brakes scrapping because I'm half released to crawl slow, the noise is the transmission. When I press brakes harder to stop, it almost sounds a mix between hydraulic action with not enough fluid or airlock, or it sounds like friction from worn or broken bearings. But it's hard to believe it's something in the transmission that is the problem because as I stated it runs like a dream 90/95% of the time. 

Even if no one can help me. Perhaps when I find the cause of the problem, this thread will help someone else. 

Forums have been a life saver many times over the years and I've always found answers just from searching and reading. This time I've had to create a thread 

[Sean84]

So these codes are always there. If i delete, they come straight back.  Even when all is going good.  I need to compare if this is normal. I'm thinking possibly it's looking for the rare edition that had the extra stability control etc 

As for the other issue, when it faults again I'll extract the code plus the sub code 

[Mr Vlad]

Some codes are a bugger to delete. I can't remember which one I had on my departed is250 but it took me quite a few attempts and a week or two to finally get it deleted.

At least now you have techstream 👍

[Sean84]

Managed to pull these codes. A tech on just answer has given me some information and i have wires to test for voltage and continuity amd insulation testing. All stuff i have no issue doing. I'll keep posted