C5 65K. Was running fine then got "service vehicle soon" followed by "security light" No start, several sets of codes each following battery disconnect overnight. Latest codes:40BCM: No Comm., 58SDM1000HC,U1064HC, 60IPC: U1160HC,U1176HC, 99HVAC: No Comm.
Could it be a faulty BCM? Where is it located?
Thanks for your help
William Mikesell

 

No Comm with the BCM is going to be a serious issue. A couple of things come to mind...Very close to the BCM is flat connector with a bridge shorting type bar in it and tape over it. This is the serial interface connector. You need to insure its on fully. Next, is there any water in, on or around the BCM and passenger footwell area? If so, the BCM probably got water into it from plugged up udders on the HVAC system. Next, check the fuses in both compartments.

 

Thanks for reply. All fuses ok. Is the BCM the "silver box" with 3 connectors? If the car sits, battery connected for about 1 hr. it will start, interior lights, security etc all normal. Codes P1626HC, U1064HC, BCM No Comm. Service Vehicle Soon message. If shut off will not re start, no lights or column lock, Codes P1626HC, U 1064HC,U 1000HC, U1160HC,U 1176HC BCM No Comm. HVAC No Comm. I cannot find the flat connector, is there a picture available. Thanks very much for your help. Most appreciated.
William Mikesell

 

Letting the car sit, then it will start is a clue here.

P1626 Theft Deterrent System Fuel Enable Circuit
U1064 Loss of Communications with BCM
U1000 Loss of Communication Undetermined
U1160 Loss of Communications with LDCM
U1176 Loss of Communications with RFA

Two thoughts off the top of the head as such, one: check your battery level with a meter and the ignition off by measuring across the battery. You need at least 12.5vdc there for the computers to work, therefore the age/status of your battery comes into question. two: In the door accordian tubes, there is a connector in which the serial data buss wire is present. That wire can become lose and cause issues so you might want to give the tube a shaking and see if anything changes.

Sorry, I don't have a picture of the serial buss star connector but Bill Curlee does. Hopefully he'll see this thread and offer his expertise to you. I'm still leaning towards that star connector as a possible cause though. Yes, the silver box is the BCM and this star connector is right there close by. You didn't find any water on or near the BCM or the carpet there? The no-start is being caused by the P1626HC which is shutting off the fuel pump and that is happening due to the no BCM comm.

 

Thanks for help. No evidence of water whatsoever. Battery is less then a year old Delco OE, fully charged. Now no start at all, no interior lights or security message. Same codes as before. Still can't locate the serial buss connector. Near the BCM is 2 connectors that had black tape. Checked ok, no corrosion or damage. Is it possible I have a bad BCM?
I did Bill Curlee's repair on the 2 ground circuits under the hood. Re checked all fuses good.
Thanks again
William

 

Ok, back up key used. Codes: 40BCM: No Comm., 58-SDM: U1000HC, U1064HC 60-IPC: U1160HC, U1176HC, 99HVAC: No Comm., AO-LDCM:
U1064H, A1-RDCM: U1064H, BO-RFA: u1096H,U1000H,U1016H. No interior light, security message but did display"Service Vehicle Soon"
Thanks so very much for kind help.
William

 

Did you ever check all of the fuses in both fuse boxes? The next step will be to start disconnecting various modules then run the codes again to see if the BCM starts talking. I would start with the SCM which is the seat control module under the driver's seat.

 

Checked and double checked every fuse in both boxes, all good. I will start with the seat module, where would be next? Just curious to BCM ever go bad?
Thanks
William

 

I can't see the car starting up after 30 minutes if the BCM is bad. Not saying it can't happen but who knows. I think it would be prudent to send a PM to either/both Bill Curlee or Lucky131969 about this thread and ask for assistance. 8VETTE7 might be just as good too and be able to assist. About the only thing I can do is to point a possible direction.

 

To the LEFT of the BCM,,, there are TWO thin connectors. They are the STAR Serial Buss connectors. The connector with the least number of wires is the serial buss for the Door modules and the seat module. The TOP of the connector is a shorting strip. Remove the top of the connector with the least numper of wires.

Once its removed,, CLEAR ALL THE DTCs and then see if the car will start. You will get door module and seat module NO COMMS (expected)


Post results!

BC

 

I removed that connector still no start. Codes: 40BCM No Comm, 58SDM(3)U1000HC,U1096H,U1064HC 60IPC U1176HC,99HVAX+C No Comm, AO LDCM No Comm, A1 RDCM No Comm, Bo RFA (3) U1096H,U1000H,U1016H, . I plugged it back in Codes: 40 BCM No Comm, 58 SDM (2) U1000HC,U1064HC, 60 IPC (2)U1176HC,U1160HC, HVAC No Comm, AO LDCM
(2) B2284H, U1064H, A1DCM (2) B2285H, U 1064H.
Thanks so much for helping me.
William

 

If your serial buss isn't compromised,, you must be missing a voltage. Most common issue is a bad /dirty ignition switch. Follow this post and read the the voltages at the "Hot in Run & Start" supplied fuses and make sure that you have full battery voltage on those fuses:

-C5 ignition Switch repair - http://forums.corvetteforum.com/c5-t...ch-repair.html

 

Ok Voltage #19=12.1, 18=12.1,17=12.1,22=12.1,16=12.1 13=12.1 inside #21=11.9 #22=11.9 # 19=12.0
Battery voltage 12.1 It has dropped over the last 5 hrs. at about 4;30 it was 12.5. Also every now and then the interior lights come on and the car will start normally. The last time that happened 2 days ago I thought the "problem resolved itself" but when I touched the BCM I heard a distinct "click" the lights went off, no start ever since? Could it be a bad BCM?
Thanks for you kind help.
William

 

Disconnect the battery.. Pull the BCM (all three connectors) and inspect the BCM, Plugs and wires for damage. Make sure that all the connectors are fully connected and reconnect the battery and see what happens. Clear ALL the DTCs. Carefully move the wires and connectors and see if you get the same intermittent problems.

BC

 

OK as instructed. Codes: 40 BCM No Comm., 58 SDM (2) U 1000C, U1064HC, 60 IPC (2)
U1160HC, U1176HC 99HVAC NO Comm, AO LDCM U1064H A1RDCM U1064H. Carefully wiggled each wire of all 3 connectors & the star connectors No Change No Start. I had slow charged the battery overnite, new readings #19 13.1, 18 13.1,17,13.1,22 13.1, 16 13.1, # 21 12.5,22 12.5 19 12.5.
Thanks againfor your help it is VERY much appreciated.
William

 

I did check the condition of all 3 connectors, no corrosion, bent etc. I also checked continuity between the wires leading in and the plug outlet all good. Do you think the BCM is bad? A forum member has a used one for sale.
Thanks for your kindness.
William

 

Still no start, no interior lights. Battery voltage 12.5, fuses all good, wiggle test wires on BCM and star connectors no change, no evidence of water or corrosion. Todays codes: 40 BCM No Comm.,58-SDM (2)
U 1000Hc, U1064HC, 60 IPC (2) U1160HC, U 1176HC, 99 HVAC No Comm, AO LDCMU 1064H,
A1 RDCM U1064H " Service Vehicle Soon" Please Help
Thanks
William

 

Well,,,, If it were me, and as much as it cost for a BCM and you will have to get any RPO Codes programmed into the new BCM with a GM Tech 2 and sync it to the BCM,,,,, I would remove the BCM, open it up, remove the board, examine the circuit board and if that looks good.. probe the BCM fuses to make sure that there not blown and the fuses have the correct voltage on EACH or the three fuses.

Check the fuses FIRST! Use a METER and see if theres battery voltage on each fuse..

BC

Bill

 

Bill: Thanks for all of you help. I replaced the BCM with a used one from a 2000. Completed the re-learn procedure, started ok. Deleted the existing code, ran diagnostics, " no codes". Everthing works normally except when you release the E brake the headlights come on, I will take it to the dealer for reprogamming. I would be happy to send you the old BCM if you would like to check it out. Again a heartfelt thanks.
William

 

Looks like your "gut" instinct served you well. Glad you got it up and running. Yes, you will need the RPO codes programmed into it.