I haven't checked the manual.

I would always favor position over color. Wiring harnesses can easily be made incorrectly and still work provided pinouts are the same.

Moving forward, always check voltage between target pins first. If you detect a voltage, you probably shouldn't check resistance.

Check fuses.

 

It says to check each position independently, and that is what I did. According to the manual, only the 06 and 07s have that wire position, but it doesn't say whether you're still supposed to check position 9 or not (it has no wire). Actually, it has a * next to where it says 9 BRN and if you go towards the front of the IMA section it says 06 and 06 only. My manuals are for the 06-11 models.




I did recheck and don't have any more DTCs so hopefully I didn't damage anything.

I also found this in the 09-11 Electrical troubleshooting manual:


Now I think I understand I only needed to check position 2 for this step in the diagnostic tree.

Is 4 ohms resistance considered okay for continuity? Now step 19 says to check voltage between 18 and 19 and body grond on the MCM 20P connector within 1 second of switching the ignition to ON, but here again, my 09 only has a wire at 18 so does that mean I only check at 18? It must be, because that's the only Ignition assist power source.

 

Well, hopefully I went through the steps correctly. I just put in an offer for a BCM on eBay.

 

What led you to the conclusion the BCM is faulty? MCM failures are more common, and given that you could read the 11 tap voltages with your scan tool, that implies the BCM is functioning.

 

According to the steps I went through in the service manual, the next step is to swap the BCM, so I just ordered one from an eBay seller with 100% positive feedback that says it came out of a working vehicle for $100.

 

Also, I started to wonder if those tap voltages were stored in the PCM from the last time the system was working, because the whole battery voltage measured 68V at the positive and negative leads, which is much lower than the total of those tap voltages (I know I could check each one at the orange connector if I wanted to).

Anyway, I believe the defining factor here going through the diagnostic steps was at step 19, there was not 12V battery voltage at position 18 when measured within 1 second of turning the key to the ON position. I measured this by using a sewing pin at the back of position 18 with an aligator clip connected to the positive lead on my multimeter, and another aligator clip clipped to the nearest ground with the other end connected to my negative lead. I then reached over and turned the key to ON, and tried it a few times to make sure i got consistent results. It measured barely over 1V and then started dropping lower. Then, in each step after that, all of the other continuity, voltage, and relay tests checked out, so it seems to have something to do with the BCM at the 40P connector side.

After swapping the BCM if there are still DTCs I'm supposed to start over at step 1, so I'm considering just ordering an MCM too because going through all of those tests was such a nightmare. That said, it probably wouldn't be quite so bad the second time around now that I understand a little bit more about what I'm doing.

 

First, I'm 99% certain the PCM does not retain those values, the BCM does. Given the number of times you've disconnected the 12V, it's essentially impossible that tap voltages could be from two years ago.

The only time you get battery voltage at the main leads is if the system says the battery is functional and the isolation relay is closed, which connects the IMA battery to the HV system. If the engine was idling at the time of the measurement, you were seeing the IMA motor output, 68V. If you were measuring 68V at the main terminals with the engine off. That is extremely abnormal. Exercise extreme caution.

Checking battery voltage on the other side of the relay would answer the question. Checking a single tap or all of them (which might take you 60 seconds) would establish the truth.

Glad to hear you've ordered an MCM as well. At least you'll have it on hand.

 

Hi Steve, I just saw your response today. The voltage at the relay was part of the diagnostic process and it tested good. I got the substitute BCM today but no change in codes, all of the same ligts. However, this time with a fully charged 12V battery I noticed that when the car is running above 1500 rpms and I'm looking at the live data, the 12V battery voltage will not go over 11.95V when previously I was certain it would go above 14V. Does this indicate I should replace the 12V? I was already considering going to the 51R battery next time I needed a new one anyway.

Also, I actually did not order the MCM yet, and they sent me the "wrong" BCM in that I specifically ordered one that the part number ended in A11 knowing it was manufactured at a later date and they sent me an A07.

 

HV voltage at the relay, not 12V.

When you measured 68V, where did you have your probes?

I don't expect you'll ever see 14V with the issues you're having. If the 12V light is on continuously, you're not going to see charging. The car isn't/can't charge the 12V. The car is only a load to the 12V. It's why it's gone dead several times as you described.

If you rev and hold 2000 rpm for 30 seconds, and the 12V light stays illuminated, no 12V charging.

 

I double checked and I definitely did see 14V before.

Today I checked the HV battery voltage at the main leads where they connect to the junction box. With the key in the ON position it read about 40V, when I stated the car about 80V. I tried checking the tap voltages but I was struggling so I took a break from that.

I've been searching if there is a way I can check the flash codes in case my scan tool is missing something. When I try to jump in pins in the DLC I only get the codes for the blower motor, which was just a loose connection. Specifically, I'm wondering if I actually have a code U0028 (107) because in the repair solutions software on my phone that works with my scan tool, one of the U0110 codes says it's for BUS OFF MCM, not just lost communication like the rest of them say.