No start because of body control module
11-16-2010, 05:50 PM
#21
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thanks for the thoughts. According to the manual, the start solenoid winding does draw between 10 and 15 amps? Pretty strong solenoid! This stuff used to be very easy when everything was inside a hoffman enclosure but in a C5 Im finding it very hard to trouble shoot, e,g. getting to components. Guess my next step will be to jack it up and put a VOM on the start soleonid (A) terminal, make sure the BCM is not in sleep mode and give it a try. then if I see B+ on the solenoid coil but no contact closure, know at least that needs replacing!
Originally thought there was only the Start ckt (cell 30) and the TDR logic, e.g, ign switch, clutch switch and BCM ground switch which looks to be controlled only from the PASS KEY input? But based on this sleep mode, must be more to look for. Thanks
Originally thought there was only the Start ckt (cell 30) and the TDR logic, e.g, ign switch, clutch switch and BCM ground switch which looks to be controlled only from the PASS KEY input? But based on this sleep mode, must be more to look for. Thanks
11-25-2010, 11:06 PM
#22
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Rick, I would just jump the theft deterrent relay first and see if it cranks. If it does, the problem could be the BCM, the theft deterrent relay, or the ignition key resistance reading piece (bad contact or frayed wires in there). I think those would be the only possibilities if you jump the relay and it cranks. But if you read all that current to the starter solenoid, I think the problem would have to be the starter.
You could also whack the starter with a hammer with the key on start, which will make them work sometimes.
You could also whack the starter with a hammer with the key on start, which will make them work sometimes.
11-26-2010, 12:01 AM
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I just read how to put a resistor in the VATS resistor circuit, and damn, wouldn't it be easier to put it in right at the BCM than taking the whole console out? I don't have the schematics at hand, but the two wires go straight from the BCM to the ignition switch right? If so, than I don't see why anyone who was going to solder a resistor in wouldn't just do it at the BCM. It's much easier to get to.
11-26-2010, 06:48 AM
#24
I just read how to put a resistor in the VATS resistor circuit, and damn, wouldn't it be easier to put it in right at the BCM than taking the whole console out? I don't have the schematics at hand, but the two wires go straight from the BCM to the ignition switch right? If so, than I don't see why anyone who was going to solder a resistor in wouldn't just do it at the BCM. It's much easier to get to.
11-26-2010, 10:03 AM
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Yea, but in the C5 since the ignition module is in the dash you can't get to it without taking the center console piece out. That's what the instructions on a thread in here say to do. It's about 6 bolts, I had to do it to put a new receiver in and I found it to be a pain. I'll post my results.
12-01-2010, 09:42 PM
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I hooked up a used BCM from a 2000 in my 99, did the key on, off procedure (turn ignition to on for ten minutes, turn to off for 30 seconds, repeat two more times) and the car started right up. Everything works except the airbag malfunction light is on.
09-07-2012, 04:33 PM
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99 locked up
I am working on a 99 that the BCM got wet from the drains being plugged.The steering is locked, it will not crank, the windows will not work, the dash reads traction control, service engine and low tire warnings. Everything else seams to work (forgot radio lock) I could not communicate with BCM so i sent it out and of course they said it is repaired.It did have water running out of it so i did think it was damaged.i got it back and gained nothing. I checked power going into the BCM and have all except the orange wire #640. I also have no power to the # 2 fuse as well as the #37 relay (monitored ld) Any ideas ?
04-01-2021, 05:50 PM
#29
thanks!!
When the car no-starts, try this.
1) Turn key off and remove from ignition lock.
2) Pull fuse #25 (in the passenger footwell fuse/relay box), wait 5 secs, and re-insert fuse.
3) Try to start the car : IF it now starts OK, you have a BCM problem : it does not send the PCM the "Fuel-Enable" signal. It is NOT a problem with the antitheft relay, it is the "no-wake-up-BCM" problem...read-on.
It sounds like the same exact BCM 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 also checked all the BCM grounds and power feed 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.
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.
1) Turn key off and remove from ignition lock.
2) Pull fuse #25 (in the passenger footwell fuse/relay box), wait 5 secs, and re-insert fuse.
3) Try to start the car : IF it now starts OK, you have a BCM problem : it does not send the PCM the "Fuel-Enable" signal. It is NOT a problem with the antitheft relay, it is the "no-wake-up-BCM" problem...read-on.
It sounds like the same exact BCM 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 also checked all the BCM grounds and power feed 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.
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.
kim johnson (reluctant c5 owner)
07-16-2021, 12:05 PM
#30
When the car no-starts, try this.
1) Turn key off and remove from ignition lock.
2) Pull fuse #25 (in the passenger footwell fuse/relay box), wait 5 secs, and re-insert fuse.
3) Try to start the car : IF it now starts OK, you have a BCM problem : it does not send the PCM the "Fuel-Enable" signal. It is NOT a problem with the antitheft relay, it is the "no-wake-up-BCM" problem...read-on.
It sounds like the same exact BCM 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 also checked all the BCM grounds and power feed 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.
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.
1) Turn key off and remove from ignition lock.
2) Pull fuse #25 (in the passenger footwell fuse/relay box), wait 5 secs, and re-insert fuse.
3) Try to start the car : IF it now starts OK, you have a BCM problem : it does not send the PCM the "Fuel-Enable" signal. It is NOT a problem with the antitheft relay, it is the "no-wake-up-BCM" problem...read-on.
It sounds like the same exact BCM 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 also checked all the BCM grounds and power feed 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.
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.
