C5 Starting issues
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Advanced
Joined: May 2011
Posts: 75
Likes: 3
From: Edmonton Alberta
C5 Starting issues
Having issues with my car not starting. Sometimes starts first go, other times have to try several times before she starts. No patterns, very random.
I have installed new AGM battery, replaced my ignition and keys, new alternator & new coil packs and now looking at replacing my starter or at least trying to get at the ground.
Is there anything I am missing that would be the go to for this issue, or is the starter likely the best target??
Any help with this would be greatly appreciated......Thanks much in advance!
I have installed new AGM battery, replaced my ignition and keys, new alternator & new coil packs and now looking at replacing my starter or at least trying to get at the ground.
Is there anything I am missing that would be the go to for this issue, or is the starter likely the best target??
Any help with this would be greatly appreciated......Thanks much in advance!
Melting Slicks
Joined: Sep 2008
Posts: 3,117
Likes: 793
From: Espanola New Mexico
By your post I take it that it's not cranking on the first try, here are a couple of things you can try to determine what is wrong. The TDR relay sits on top of the BCM in the passenger footwell area. The socket thar the TDR plugs into has a heavy gage red and violet wire, as well as smaller gage yellow, and yellow with a black strip wires. The TDR is the relay that sends power to energize the starter, make sure the car is in Park or neutral and insert a wire jumper between the red and violet wires, if it cranks its the TDR, if it doesn't most likely your starter solenoid is at fault, hope this helps, make sure the car is in park or neutral because doing this bypasses does requirements. Hope this helps
Thread Starter
Advanced
Joined: May 2011
Posts: 75
Likes: 3
From: Edmonton Alberta
By your post I take it that it's not cranking on the first try, here are a couple of things you can try to determine what is wrong. The TDR relay sits on top of the BCM in the passenger footwell area. The socket thar the TDR plugs into has a heavy gage red and violet wire, as well as smaller gage yellow, and yellow with a black strip wires. The TDR is the relay that sends power to energize the starter, make sure the car is in Park or neutral and insert a wire jumper between the red and violet wires, if it cranks its the TDR, if it doesn't most likely your starter solenoid is at fault, hope this helps, make sure the car is in park or neutral because doing this bypasses does requirements. Hope this helps
Thread Starter
Advanced
Joined: May 2011
Posts: 75
Likes: 3
From: Edmonton Alberta
By your post I take it that it's not cranking on the first try, here are a couple of things you can try to determine what is wrong. The TDR relay sits on top of the BCM in the passenger footwell area. The socket thar the TDR plugs into has a heavy gage red and violet wire, as well as smaller gage yellow, and yellow with a black strip wires. The TDR is the relay that sends power to energize the starter, make sure the car is in Park or neutral and insert a wire jumper between the red and violet wires, if it cranks its the TDR, if it doesn't most likely your starter solenoid is at fault, hope this helps, make sure the car is in park or neutral because doing this bypasses does requirements. Hope this helps
8th Gear
Joined: Jul 2007
Posts: 8
Likes: 0
C5 Auto Won't Start - No Ground at TDR
Help! ...I am trying to get my C5 to start. New Battery. At TDR, test Jump Red to Purple rolls Starter. Ignition to Yellow on TDR is 12V when Key Turned. Yellow Black remains Open with Key turned. Is there another Relay within the BCM ie. Starter Enable Relay Control to enable Ground to energize the relay? I am missing something.
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Melting Slicks
Joined: Apr 2019
Posts: 2,466
Likes: 699
From: Clark, NJ
Help! ...I am trying to get my C5 to start. New Battery. At TDR, test Jump Red to Purple rolls Starter. Ignition to Yellow on TDR is 12V when Key Turned. Yellow Black remains Open with Key turned. Is there another Relay within the BCM ie. Starter Enable Relay Control to enable Ground to energize the relay? I am missing something.
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Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,309
Likes: 3,925
From: Cape Coral, Florida
To see if the Starter Enable Relay is being grounded by the BCM take a test light connected to battery POSITIVE and back probe ( do you know what back probing is ??) the yellow/black wire on the C3 connector (the small bottom one) pin B7 (second wire in from the end) while trying to start the car...the test light will light if the enable relay is being grounded !!
Melting Slicks
Joined: Sep 2008
Posts: 3,117
Likes: 793
From: Espanola New Mexico
Just to clarify, the BCM provides the ground to the TDR after it receives the correct signal level from the Ignition switch contacts that press against the keys resistor pellet. The security light should be off when you turn the key to the start position.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,309
Likes: 3,925
From: Cape Coral, Florida
Last edited by C5 Diag; May 8, 2021 at 12:18 PM.
8th Gear
Joined: Jul 2007
Posts: 8
Likes: 0
Verified at B7 at BCM - no ground (via test light to Bat +)
Additionally - I disconnected Battery and removed my BCM. Inspection shows no physical damage. I was surprised to see that there was no insulation between the bottom of the BCM PC board and the aluminum chassis. I added insulation and reconnected all. Verified again - 12 V on TDR C2 (Yellow) and no connection to ground on TDR A1 (Yellow/Black) on key turn. The wires at the BCM connectors are tight and spaghetti and if the Pinouts have numbers they are too small to read. If there is some kind of BCM fault - is it feasible to cut the Yellow/Black to separate it from the BCM and tag the A1 side to ground? Theoretically this should work? What is the risk?
Additionally - I disconnected Battery and removed my BCM. Inspection shows no physical damage. I was surprised to see that there was no insulation between the bottom of the BCM PC board and the aluminum chassis. I added insulation and reconnected all. Verified again - 12 V on TDR C2 (Yellow) and no connection to ground on TDR A1 (Yellow/Black) on key turn. The wires at the BCM connectors are tight and spaghetti and if the Pinouts have numbers they are too small to read. If there is some kind of BCM fault - is it feasible to cut the Yellow/Black to separate it from the BCM and tag the A1 side to ground? Theoretically this should work? What is the risk?
Melting Slicks
Joined: Sep 2008
Posts: 3,117
Likes: 793
From: Espanola New Mexico
Should work, the only downside is the loss of VATS, Vehicle Anti Theft System, so any key as long as its cut the same will start your car. You might check the wire that provides the ground to the BCM. Good luck
8th Gear
Joined: Jul 2007
Posts: 8
Likes: 0
I really don't want to lose the security VATS... Perhaps my ignition switch has something intermittent going on? If The Chip read is not consistent - would this prevent the BCM Starter Enable Relay from functioning properly? Ignition Switch Clean/Rebuild?