I got this alarm code last Friday, P0A0D. Took it to my mechanic who told me it is a high voltage interlock and indicated he would need to research it. He is a great mechanic. But, this is a hybrid issue. Not his specialty. Car died on Saturday morning. So, I towed it to Lexus dealer. The first talk I got from the dealer service rep was "We don't know what is going on." To be fair, he said this was just their initial look at it. But, he also said they already spent way over the 1 hour designated for this. During that conversation, he said the alarm code cleared and the car was functioning fine. The conversation was very weird, as if they had no clue how to service a hybrid. He actually said the alarm was gone and implied they had no idea what the alarm was, anymore. I honestly thought alarms stayed in the system, even after cleared. Since then, I've been told they only clear after 7 restarts of the car. But, he already had the alarm from me...P0A0D. As a result of this weird conversation, I did my own research and found the attached, published by Lexus, describing EXACTLY what are the steps required to resolve this issue. Now, my faith is completely jarred. It is as if they were able to start the car and therefore, hey, this weird electrical problem is now completely un-diagnosable. Bull. Electrical connection problems happen in cars. As a Lexus dealer, supposedly trained in their vehicles, charging $180 for a diagnosis, I just felt like I was headed for a ripoff of some sort. Sorry to be so judgmental. But, the initial conversation was so weird, it left me wondering a lot. You go through the connections one by one and look for anomalies like corrosion, loose connections, etc., just like the attached document indicates is what you need to do. Why am I expecting them to call me today and tell me that the main inverter/converter needs to be replaced and that it will cost $5K? I'm now looking for a hybrid mechanic in the DFW area that actually won't give me the ******* and say, "We have no idea what is going on....", when their own service literature lays out clearly the steps required to diagnose this issue.

 

Here is an update to remedy the impressions. The service sales guy is new to Lexus. He came from Porsche. But, he didn't know anything technical. Just gave me the, "We can't find anything." But, he got the actual tech on the phone with me and this guy was good. Really good. He went through the list of things and even talked with Lexus about what typically fails. Interestingly, he said the pins on the A38 plug are typically the culprit. He explained very carefully that he went through the entire check list and may have remedied the issue just by going through the checklist. After all, it is essentially a lack of conductivity at some point in the high voltage interlock system. He offered to look at it several more times this week here and there just to figure it out, because he is personally bothered when he can't figure something out. But, still no luck on the diagnosis. The car has been running for him ever since I dropped it off.

 

TL : DR the high voltage interlock circuit, if I'm not mistaken, is the thing that is completed when all the DC HV harnesses are properly connected to the inverter (i.e. DC from the battery, DC to the air conditioning motor/inverter and the battery safety interlock in the trunk of the car). Super weird, especially for a TX car. No flood damage or anything?

How did the car die?

 

I had a long chat with the Lexus mechanic on Friday and picked up the car on Saturday. He messed with it for 4 days. When this alarm goes off, there is a very distinct check list to go through, per Lexus. I've attached it here. There was no flooding or anything of that nature. Interestingly, the mechanic said that going through the check list, he may have solved the problem. The hybrid has a high voltage motor, over 300 volts. So, obviously not 12 volts. 300 volts will kill you easy. So, the system is designed to interrupt that voltage and current anytime something is amiss. In this case, it can be simple oxygenation on a contact preventing sufficient flow of electricity through the safety circuit at any of several locations. This stops the car in its tracks. It was an intermittent problem. At first, it only gave me an alarm "Check Hybrid System". The car remained drive-able. One day later, I drove it somewhere. The alarm happened. And the car would not go. Had it towed. Two days later, the mechanic was looking at it, and the alarm had cleared, and he never actually saw the problem happen. But, he went through the entire hybrid system...looking for corrosion or loose connections. He even said he called the Lexus HQ and they said plug A38 is sometimes the culprit. That is a plug under the hood serving the AC compressor. But, none of the connections were loose or even appeared to show signs of oxidation. He said that by removing plugs and plugging them back in, he may have removed minor oxidation that was not readily visible. And he said he has run into this before. And he said he rarely sees the car again after a failed diagnosis. Not sure if that is the only reason he doesn't see it again. But, it makes sense given that simple oxidation could be the problem. On the Prius, there was a problem with moisture getting through a seal and corroding a certain plug. That is not the case here. Also on the Prius, there is a red plug on the hybrid battery that is the main safety. That sometimes gets jarred open. But, that red plug in this particular Lexus is where the tire is located. The tire is covered by a plastic cover. So, if nothing is rolling around in there by the tire, the likelihood of that plug getting jarred open is low. But, a local hybrid shop who specializes in hybrid battery replacements said that more often than not, you just open this plug and close it again. But, that was for Prius and other hybrids. Also, interestingly, he did a load check on the hybrid battery. This car has 205K miles. It passed that load test. That was impressive to me.

 

Any results? I’m having the same problem. Where are these connectors?