Weird Wiring Issue 04 Z71 Burb

[TylerHagerdorn]

Hey y'all.

I've got an 04 Z71 Burb with the Flex 5.3. I was doing some cleaning and checking things out and I noticed some strange wiring. I noticed that a yellow wire on the brown C3 connector of the bcm was cut, and a grey wire was wired to it.

Using alldata I got the diagrams and the connector wasn't pinned properly to what my truck should have. Pin B1 should be yellow "Class 2 Serial Data". I found the grey wire was for the "windshield wiper supply voltage".

I hooked the grey wires back up, and my wipers only work on high. They park like they should and everything else on the switch works. However when I pulled the cowl off my wiper motor connector doesn't have a grey wire, but has two yellow wires. The diagram shows the grey wire. While I was at the junkyard I cut the connector from another Z71 that had the right wiring.

Anyways, I wired in the proper bcm connector for C3 with all wires matching. And when I went to start the truck the cluster wasn't responding, had a security light, abs light, airbag light and battery light. Had no ac, no radio, no windows, no locks, no rear air. But when I cut that class 2 wire, everything came back. I tried scanning it when I had it wired up, and had no communication. Truck ran fine though. I'll attach a picture.

According to the diagram for the computer data lines, the yellow wire goes from the PCM to the bcm. And there's a green wire on C2 at the bcm that's "BCM class 2 serial data".

Question is, why do I have issues when I connect the class 2 data wire? It's supposed to be connected. I don't have any history on things being replaced. So I have no idea what's been done. And also, why do my wipers only work on high with the proper wires connected? They had the wiper supply voltage wire running to the class 2 data yellow bcm wire and the wipers worked fine.

I'm at a loss. I hate when people mess with stuff, and I'm just trying to tidy it up and make everything good again.

Thanks y'all.

 

[Joseph Garcia]

Perhaps it is not the original BCM. I would first look at the part number on the BCM to be sure that it is the correct one for your truck.

 

[mattbta]

These _should_ be the same as AllData, but come straight from GM eSI. I notice there are two yellow on C3 - with one of them being for the security system (C3.A6). I hazard a guess that the grey wire might be from an aftermarket security system. Class 2 (C3.B1) should always be connected, methinks.

 

[TylerHagerdorn]

Alright I got sidetracked and forgot about this post. The grey wire is supposed to be from the wiper motor to connector C201, then to the wiper switch. A junkyard trip proved that another 04 Z71 Suburban had the right color wires...what I did for that was cut the yellow wire on the wiper motor plug that's supposed to be grey, and ran a wire from the switch to the wiper motor. And all is good now on that front.

HOWEVER, I'm still on the bcm connector class 2 crap. There are two class two lines at the bcm. A green wire on C2 is "bcm class 2 data" and the yellow on C3 is "class 2 serial data". So the BCM I'm sure is fine. I have two laying around in my toolbox, one I know is from an 04/05 Z71 Burb. But I don't think the bcm is the issue now.

According to the wire diagram for the computer data lines, the yellow wire goes directly from the PCM to the bcm. I hooked my meter up to the yellow wire yesterday at the bcm and the voltage was sporadic going all over from like 6 to 10 to 8 to 9 and bouncing all over the place. I know the class 2 has a bias voltage of 7, but on a meter should read around 3.9 volts. But the data it sent quickly so reading on a normal DMM isn't the best. But still that seems way off to me.

The only idea I had at the current time was to overlay the wire from the PCM to the bcm myself with a new wire and see if that fixes it. I have a video of the meter with key on engine off and key on engine running. Don't know if it'll post here or not. Just insanely strange that if I connect that wire, stuff drops off and doesn't work. But when the wire is disconnected, everything works. Maybe I'm overthinking it but I'm very ocd about wiring and want it as factory as can be.

Tried to upload the video but wouldn't let me. But it was jumping from 7-9-10-8-10-6 and back and forth on voltage at the class 2 serial data wire.