is there a bcm relay and where is itcuz i have a 98 c5 and it wont start. when i open the door the light wont come on,the trunk wont open,and the stereo wont work then when i try to start it it wont even turn over. if i just leave it in the acc on the key it will say all these alerts like low fuel,reduce engine speed, ect but if i disconnect the batt and reconnect it it starts but if i shut it off and let it sit 4 like 7 min it wont start till i take the cables on and off again any ideas....

 

and where the grounds 4 the bcm

 

You mentioned other body control issues???? If the door changes the conditions,,,pop out the accordion tube ( it comes out real easy) and carefully examine the wires and connectors. Separate the connectors and clean them and seal up any damaged wires.





Don't ask me why but that bare ground wire seems to have something to do with the issue. I been told that is a stereo speaker shield/ground wire. I covered the bare wire with liquid electrical tape and have NOT had any issues since.

I also had a no start condition when the door was shut and my DIC and dash lights also spazed out. If I were you, I would check the door wiring issue out before you get too deep into other circuits.

When the DIC is accesses, do you see any U series DTCs?

If that doesn't fix it, try this

There are BCM issues that can cause what your experiencing. Its NOT a relay per-say but a driver circuit issue. The BCM controls the Theft Deterrent Relay (TDR) which actually applies power to the solenoid to power the starter motor.

You need to locate the TDR in the passengers foot well. Its above the BCM on the fire wall. It has four wires RED PURPLE yellow & yellow/black.

You can see TWO relays above the BCM. The one to the left is the TDR:



The starting schematic is posted below:



When the problem starting the car happens, try his:

With ALL the necessary steps completed to start your car, have someone short the YELLOW/BLACK wire to ground and if the car starts, you most likely have a BCM issue.

 

Try what Bill Curlee suggested, but it sounds like the same exact problem I had with my 01 6spd. I did a lot of troubleshooting and this is the "story". And no, my BCM never got wet. I allso checked all the BCM grounds and power fed circuits, and my door wires.

When everything works properly : the BCM is the "Power Master" of all the computer boxes hanging on the serial data bus. When you shut the car off, then remove the key, and then open the door, this starts a power-down timer in the BCM. This timer is about 20 or 30 minutes. If the BCM sees no activity (key put in ignition, a door open...) during this 20 minute period, it sends a "Power Sleep" mode signal to all the other modules on the bus, and they go into a low-power sleep mode (so the battery doesnt get drained). The BCM goes into a sleep-mode too, but it still has enough functionality to recognize that a door has been opened, or a key was inserted into the ignition switch, which terminates this power-down timer and wakes-up all the modules. This sleep functionality of the BCM is also there for the anti-theft horn alarm. In sleep-mode, the BCM can also recognize a hatch-release request from the RF remote control (key fob), and then the BCM activates the hatch release relay. (The hatch release signal comes from the remote radio receiver and is transmitted to the BCM on the serial data bus.)

If you have this no-start problem, the issue is that the BCM does not come out of its sleep mode : it does not respond properly to the door-open switch inputs (or the key-in switch input, or the hatch release request). If you try to start your car before this timer runs-out (as evidenced that the interior lights come-on when you open the door), the car will start. If this timer expires, and all the modules (including the BCM) go into sleep-mode, your car won't start. The problem is internal to the BCM : It does not come out of its sleep-mode when you open the door, or stick the key in the ignition (the "key-in/out" switch). If you pull passenger footwell fuse #25 (the one shared by the Instrument cluster and the BCM), and then reinsert it, this forces a power-on-reset of the BCM logic, which forces it to come-up in the waked-up state, and now the car will start. Fuse #25 is the power feed to the BCM logic/CPU circuit. So that I could still drive the car, I rigged-up normally closed pushbutton switch in-series with fuse # 25, so I could reset the BCM before I started my car. And yes, I verified that all the correct power-feeds, grounds, and switch inputs were present at the BCM connectors. I even bought a spare BCM module, and started tracing out its internal schematic, in an attempt to find the defect of the wake-up circuit.

Now for the weird part. After using my pushbutton BCM reset switch for many months, I noticed my BCM began to behave normally. I noticed that the interior lights once again came on when the door was opened. I still have my pushbutton wired into the fuse-box, but have not had to use it anymore.



You have 3 options to fix this :
1) Kludge-fix it with a pushbutton switch
2) Replace the BCM with a new one (get the correct pn, there are 2 or 3 BCM part numbers used, depending on the model-year), but you must get the replacement BCM programmed by a GM dealer for your cars RPO options. Because the car won't run without this programming, you will have to have a GM dealer do the BCM replacement and reprogramming.
3) Find a used BCM, of the correct pn on EBay (or wherever), whcih has the same options as your car does, and therfore already has the correct RPO programming.

 

thanx alot man ya mine works if i pull #25 also.can you send me a pic of the switch so i can see how you did it im not really good at that kinda stuff thx.

 

My pushbutton kludge fix : Take a mini-fuse, cut apart the plastic and save the metal pins (cut the fuse element that is between the pins. Then solder on a length of insulated wire, from one pin to an automotive blade-type fuse-holder. The other side of the fuseholder pigtail to some more wire, to the Normally Closed (NC) contact of a momentary bushbutton switch. Connect the other terminal of the switch (C) to another length of insulated wire, the other end is soldered to the 2nd fuse pin. Install shrink tubing to insulate all the connections. Install a blade fuse (same Ampere rating as fuse #25) into the added fuse holder, then plug the mini-fuse pins into the fuse-box, where fuse #25 was. To start your car, push and release the bushbutton, then rotate the key and start. Since I don't now need to use the bushbutton, I just coiled the wire up in the pasenger footwell, tucked out of sight in case I need it again.

Note : The antitheft horn alarm will not be functional if your BCM has this wake-up problem, nor can you pop the hatch from the keyfob or the dash switch unless you hit the pushbutton first.

 

thx man ill try it.wow the bcm for this this model corvette is a real piece of s***lol thx again 4 the info you helped me more than anyone else and saved me a ton of money. next time im in town ill buy ya a beer