donjegge

Hi Bill thanks for your guidance. I have done the DTC dozens of times and have never had issues. Unless I have suffered diminished capacity, I'm pretty sure its a no com issue.

Battery is fully charged and functioning correctly. There is no voltage showing on analog or digital display. We can squeeze the bcm connector and get some data flowing, but in a resting state, nothing flows.

We will measure resistance on each wire on the star connectors and report back.

dadaroo

Here is a picture and the circuit design. Two connectors that are "tied" together by one wire.









Star Connectors

Bill Curlee

If it were me, I would carefully examine the BCM connector female pins, the solder connections on the circuit board for each plug, the wires that are crimped into each pin in the suspect connector.

Make sure each connector is not cracked or broken.

There you will find your issue.

Bill

donjegge

We traced all star connector wires end to end, and found no issues. We checked all bcm plug connectors visually and by measuring resistance at plug and probed 8 inches up the wire, with no luck. At this time we are assuming bad connection at bcm board, and went forward and ordered new BCM unit. Do you know if anyone on the forum handles programming, or is it a mandatory 200 trip to the local dealer? I'd rather pay a member than an stranger, even if its the same money.

Bill Curlee

You will have to do the GM BCM/PCM sync prcedure. Its mandated that GM (or any other auto manufacture) cant have a manufacture only procedure to get the car back on the road.

Preform the SYNC PROCEDURE and the car will start and run.

IF,,,,,,,,,,,, you have any GM RPO codes (example F-45 Real Time Dampening Shocks) ,,,, to retain that factory option, it should be reporgrammed back into the BCM

As luck would have it, that option almost programs its self bacm in if the module is connectd. )

Anyway,,,, hopefully someone will provide that procedure as I am on a business trip and dont have access to it.

Is simple to perform. Just make sure that you have a good fully charged battery as there will be several 11 min parts of the procedure.

Bill

dadaroo

BCM/PCM RELEARN PROCEDURE


You will need to conduct the PCM/BCM relearn process. This matches their handshake ID's and allows them to talk to each other.


Replace the BCM then:

1. Turn on the key for 11 minutes.
2 Turn off the key for 30 seconds.
3. Repeat 1&2 two more times.
4. Turn on the key for 30 seconds.

The car should start and run with the new BCM.

This will sync the PCM to the New BCM

Once the BCM and PCM are sync'ed up you can start and drive the car. However, RPO's that the car has installed MUST be programmed into the BCM using a TECH II. RPO's on the car must be turned on in the BCM. For example if your car had options like the F45 or F55 suspension, the BCM must be told its there. Similarly with wheher the car is a manual vs automatic, etc. You can get the RPO list from the Glove box door and if you have someone that has a TECH II you can do that yourself.

donjegge

Well this is interesting.

I found a dead battery on the car today, where there had been no problem. So I make a note and move on. I fully charge the battery, and move on.

Plug new bcm in and go thru programming.
Success!!!
Gages dash radio and ac all perfect, so now i figure I'm good but then i notice the parking lights wont go out.

So now i have 2 new symptoms (untraced short and parking lights staying on) but at least the new bcm is working fine.

But then....

I start the car up again and all the dash lights and gages go stupid and i'm back at square one. And the car wont run for more than a few seconds. I try to re-program again, and the car wont run for more than a few seconds. Plug the old bcm in and the car runs fine but the dash problems still exist. I do believe the old bcm was flakey, because a wiggle of the connectors caused conditions to change, and with the new bcm that does not happen. Obviously we have to be careful here, these wires arent exactly heavy gauge.

Now i will track down where the short is now, and we'll open up the fender access to the ecm to make sure that no mice have taken residence up there and damaged things that could be making us insane.

Additionally we had previously tested ecm to bcm connections and had no resistance.

This is getting real challenging.

Don

dadaroo

Can you pull codes with the new BCM?

I would also try opening up the Star Connector and ONLY tie the PCM and the BCM together. See if the car runs OK.

donjegge

Dadaroo,

Bridged just the pcm to bcm.
Car starts and keeps running.
Then connected the star connector.
Car kept running, radio guages and heater were fine. ABS, TCS ALbtrakes had issues.
Turned car off, restarted and shut down.
Seems like one of the modules is preventing start (fuel shutoff relay) , but doesn't prevent running. We are going to isolate the voltage drain circuit and will advise on codes too.

dadaroo

Would you pop the top off the 4 wire star connector and try to see what that does for trying to start and run?

I don't know what would cause what you are seeing outside of the PCM,BCM, or serial bus. Will do some more thinking.

For checking the battery drain I always recommend one first measure it and then remove the12V feed from the engine fuse box to the passenger fuse box. Measure the drain again to see if it has changed.

This feed is a big red cable. You will find it starts at the rear of the engine fuse box at a stud with nut. The red cable feed from the battery also lands there.

donjegge

Well dadaroo and Bill, we regrouped and bought a new battery, charged it fully, reprogrammed the bcm. We are not throwing any codes and the car starts and runs fine. Drain of 40 milliamps. Not optimal, but certainly workable.

We are also experiencing the dreaded service column lock / remove key 10 second message and cant go faster than 2 mph, so I just ordered the LMC5 and should have it by this friday. I will post results.

dadaroo

Hope all goes well.

donjegge

Dadaroo and Bill, final update. ( I believe)

LMC5 fixed the dic message and allowed me to drive the car to the dealer.
After programming the bcm at the dealer, I got the service steering column message and an undocumented B2908 current fault code, but was able to drive the car.
When home, we removed the LMC5. Messages cleared and no faults. All good now.

When I installed the new bcm, apparently the default mode was for a manual and i could not drive my car without suppressing the shutoff with the lmc5. After programming the bcm for an automatic, the lmc5 confused the bcm.

Thanks again for your tenacity and guidance in diagnostics.