My Tahoe won't start after I disconnected the 12V battery

On the display it says service hybrid system so I checked the codes on the Torque app on my phone and I get P1AF4 and P1AF6 codes. If I clear them they just immediately come back and there are no other codes. I also checked the 12V battery is fine and the orange safety plug is fully inserted.

I have been doing a lot with the hybrid battery lately (pulled out replaced cells, was running the hybridautomotive Prolong charger/discharger for a few cycles to balance the cells). I have used the prolong thing before though and it hasn't caused any issues before and I was driving around with no problem after rebuilding the battery. The last thing I did was just unplug the 12V battery, I thought it might be a good idea after the most recent prolong charge/discharge cycle and I didn't expect it to break everything. In the torque app I am still getting readings from all the cells and everything looks normal.

The internet doesn't seem to have much info on these codes except that they might be something to do with battery isolation. If I check with a multi-meter between the + or - side of the battery and the other side of the isolation relay (at least that is where I think I was probing, I found this picture on another thread) and it seems like I am measuring half the battery voltage and then it starts to droop and slowly drops down if I just leave the meter connected but it never went right to zero volts. What is normal to probe at these points? (this is with the orange plug inserted)

Trying to figure out, is there actually an isolation problem or is the computer just being dumb after the 12V was disconnected, because everything was working fine until I disconnected 12V

thanks for any help!

unless I can get some ideas on how to fix it, its off to the dealer monday morning, I am scared to find out what this will cost me

 

Disconnect the voltage sensing harness plug from the computer.

Check and record voltage from indicated (-) terminal to case.

Check and record voltage from indicated (+) terminal to case.

 

Thanks for the help Keith,

I took the cover off and did a bunch of probing this morning, I found that with the orange safety plug out the voltage from either the + or - to the case is low, around 0.05 to 0.1V at most. With the plug in on the negative side when I first touch the multimeter it jumps to around 1 to 2V then starts draining through the meter I assume.

I am guessing this is too high to be normal?

I tried unplugging everything I could possibly find to isolate it and so far no luck. Things I unplugged: top orange connector (voltage sensor plug to the computer box thing), a couple small grey plugs near the bottom, some kind of black relay thing along the bottom on the seat side, I removed the large +/- cables from the isolation relays and probed directly on the batteries, removed the two orange wires mid pack that go to the safety plug and replaced with a shorting bar (in case the problem was the safety plug itself), removed the grounding wires that are bolted to the bottom of the case on the side of the battery that faces the seats.

The only thing that ever removes that 1-2V is disconnecting the mid pack wires/orange safety plug

I am guessing that means the short is in the second half of the battery but I can't find where it could possibly be coming from, everything seems disconnected unless I am missing something. Next step will probably be taking the whole pack back out of the car.

Just to double check though is this 1-2V leakage my problem?

 

With sensing wire unplugged from the computer, check voltage from the 10th module from each end to the case.

 

thanks, I tore everything all apart again and I am wondering what is normal for leakage now. I found the readings I was getting were all over the place until I realized I need to actually securely hook the meter probes and also not touch them because I was creating a tiny leakage path. With that taken care of I was measuring consistently 3.3V from the neg probe to the case.

I left the meter plugged in while I unbolted the pack from the truck and moved it up and out of place and it stayed consistent at 3.3V the whole time. I then started disconnecting bus bars moving from the negative end and the voltage would drop, 3.3V at end, 1.26V at 10 from the end, 0.72V at 18 from end, 0.5V at 22 from end.

I put the busbars back and bolted up the orange cables and now it is 1.4V, somehow the extra charge seems to have drained off? After leaving the meter on for a half hour it is now under 1V

I don't know what to expect as normal here, is there a spec for this?

Also does it make sense that it could have built up some charge and I am slowly draining it off? once it gets under a half volt I am going to connect the battery back up and see if I get codes.

thanks

 

With the sensing harness disconnected from the battery computer, all modules should read 0V from either terminal to case.

Given the work done, have you re-installed each screw that secures each module to the case bottom (40 total)?

 

yeah I am still surprised there is a little leakage voltage there, yes all screws are installed except for one that was broken but that cell still has contact (someone ground down the bolt) and the second bolt in that cell is installed

where would the leakage be coming from if I have everything disconnected? is it through the cells themselves?

 

connected battery back up and still getting those same two codes. I noticed that after turning on the key to try to start now there is 12V between the hybrid battery negative and case ground. If I unplug the big black plug that connects the battery to the car the 12V goes down to 0.25V and if I plug it back in it stays down until I turn the key on again.

I am thinking the leakage thing may be chasing a red herring since it seems to be 0.25V now, is it possible the 12V I measure is a clue to something?

 

Leaking modules is a thing. They leak from the interface between the threaded insert on the bottom and the plastic housing. This creates a path to ground and triggers codes since the HV and chassis are isolated.

IMHO, you should remove all bus bars and check each module (-) to case bottom. If you measure any voltage whatsoever on a module to the case bottom, it needs to be replaced.

 

oh man this just keeps getting better lol, I have spent so much time and money on this truck. I just finished replacing all the cells from these guys: https://www.hybridreconditioners.com/ the truck was running fine at the time but the mileage was still pretty crappy and I noticed in the torque app that the cells didn't seem to be super well balanced so I put the truck on the prolong charge/discharge thing before this all happened, not sure if that caused a cell to start leaking maybe?

I did quite a bit of research before and these guys seemed to get good reviews and it sounded like they were doing the right thing, any experience with them? I saw in another thread you recommended bumblebee

What do you typically recommend for these old vehicles? I am wondering if I am just continuing to throw money away and should try to get a refund and buy a brand new battery or brand new set of modules?