P0A0D to no end…

Good, there our manuals agree. That's the step 16 test, where OK ► replace power management control ECU.

Back in your post #13, you had only mentioned the NG result for step 7 (where NG ► do step 16).

Now we're back on the same page.

 

If you still have P0A0D, it just means there is something trickier going on with the dead-simple series interlock circuit that we didn't catch on the first pass.

With the replacement power management control ECU in there, what is the step 7 test result now? That's the one that was NG, with the reading much lower than 10–14V, before you replaced the ECU.

 

I know there's already be a hundred or two posts in this thread if you only asked one question pre post.

What are you using to cycle and load test your modules?

Back at the very beginning of this thread after you put your pack back into the Lexus. The fan stayed on for the entire time the car was on. My first thought was the packs re assembly.

Than you add that you serviced the EGR. OK. I guess I'll assume this is the first time for both those services>

 

OK, so that was the NG result that led you to step 16, where you checked the resistance between A62-35 and A19-32 and found it to be good (below 1Ω), leading to replacing the ECU.

However, with the ECU replaced, you still have an NG result for step 7. Changing the ECU did not fix that.

This is where it becomes important to read troubleshooting steps actively, as if you are following along in the reasoning of the engineer who wrote them.

In step 7, you have unplugged A62 from the inverter, so none of the interlock circuit within the inverter or back to the battery is in play. You are simply testing the far end of a wire that's attached to A19-32 at the ECU.

The ECU is the source of 12 volts onto that wire, which therefore should read as 12 volts to body ground when you measure at the A62 end. But the mere act of attaching your voltmeter pulls that voltage down by about half.

That would make you think there is quite a high impedance in there somewhere: either in the voltage source within the ECU itself, or within that length of wire from A19-32 to A62-35 (or in that A19-32 pin-to-socket connection). A typical voltmeter has an impedance in the megohms, so for that to pull a voltage down by half, you'd expect to find a similar impedance of megohms either between the ends of that wire (a wire break or near-break), or in the ECU itself.

So the next easy thing the engineer had you do was disconnect the other end of that wire and measure the wire's resistance end to end. You got under 1Ω, so the wire looked good. The manual then, following the most-likely explanation for all that, said "there's a high impedance here that can only be in the wire or the ECU and doesn't seem to be in the wire, so swap the ECU."

Manuals are written to follow the most-likely explanation because it's, well, most likely. But here you've put in a different ECU and still have the same halved voltage reading at the far end of that wire. You still have the problem quite narrowly boxed in—no possibility other than that wire, those connectors, or the ECU (again!)—but haven't pinned it down yet.

Do you own a set of backprobes? I'd be inclined to leave A62 disconnected (as in step 7) and backprobe A19-32, and measure the voltage to ground at that point. Is it more like 12 then, or already pulled down to 5.7?

If it's already pulled down, I would next want to measure the voltage to ground that this ECU puts out on that pin with that wire disconnected. This may not be as simple as just unplugging A19 and measuring from that ECU pin to ground, because A19 might carry other things the ECU needs (like power). So it might mean backing terminal 32 out of connector A19, so you can plug the rest of A19 back into the ECU and then poke a probe in where terminal 32 went so you can measure from the ECU pin to body ground.

You can see why further tests like these weren't in the manual—99 and 44/100ths percent of the time, if you measure low voltage at A62-35, you're going to spot an obvious high wire resistance in step 16 or have a bad ECU output.

You just happen to be in one of those situations proving that weirder stuff in nature can sometimes happen. The manual can't really try to have every troubleshooting procedure include extra test steps to cover all the super unlikely weird cases, 'cause it's already 7000 pages long as it is. But this is where the active reading comes in, because once you've looked at step 7 and step 16 and understood what the engineers were telling you there and why, now when you find yourself in a weird case those two tests didn't get to the bottom of, you can think out what your next tests have to be.