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.

 

I think your problem started with a diy battery rebuild and is likely to be resolved there. I assume no Ready is still a problem. Do the battery voltages still read incorrectly with Techstream? Absolutely sure the orange disconnect is pushed in, snapped closed and then pushed sideways?

So you had at least one user induced error. I would verify what damage could have occurred when fan power was sent to the wrong place and vise versa.

 

Keep in mind that when A62 is unplugged, as in the test step #7, nothing in the traction battery is in the picture. The service plug/interlock switch is out of the picture. The inverter cover interlocks are out of the picture. The inverter to battery wiring is out of the picture. Step 7 is testing, in complete isolation, the ILK output of the ECU and the wiring from there to the inverter, and nothing else.

So in post #30, the voltage has been confirmed also low at the ECU end (pin A19-32). Still with A62 unplugged, right?

It's about more than confirming an expectation, but finding something out. it could also have happened that you measured 12 volts at that point, which would have meant a high impedance had to exist between the ends of the wire (an intermittent one, as you measured < 1Ω in step 16).

But having measured the same voltage at this end, you have largely ruled that possibility out. It remains to test whether the low voltage is seen on the ECU output pin with the wire disconnected (that is, terminal A19-32 backed out of the connector shell, as I suggested in #28).

For this, too, I don't really have a prior expectation. It will either be the case that the ECU always outputs a low voltage on that pin, or that it outputs 12ish volts when no wire is attached there and is only pulled down when the wire is attached. The two outcomes are both possible and would tell us different things, suggesting different next steps.

That's the next thing I'd test.

The low voltage on ILK has been seen now with two different ECUs. Just so I have the order of events straight, was the replacement ECU tried only after discovering and correcting the connector mixup at the back of the car? Or could both of those ECUs have been in the car at times when the connectors in back were still mixed up?

 

I tried following through this thread, but just a bit of clarification..
Was the car working at any point prior to battery disassembly?
Did you do any work at the inverter?
When you installed the safety interlock socket/cable assembly, did you plug in the small connector to the interlock socket?
When you installed the orange safety switch, you performed all three steps? Insert, rotate handle, slide handle sideways to push jumper wire into the interlock plug?

I've seen many times where a DIY rebuild goes haywire because the small wire was never plugged back into the interlock switch socket, so the car would always think the safety switch wasn't installed. I think on the Gen 3s, there's also brown plastic resister (or whatever) mounted below the safety switch. I don't remember if they use similar connectors, but it may be worth checking that you've got them in correct positions..

 

Keep in mind that the OP's diagnosis has already proceeded as far as step 7 in the P0A0D troubleshooting, at which point everything in the back of the car (in fact, everything except the power management control ECU and the wire from it to the inverter) is eliminated from the picture.