Hi All,

If I leave my 1999 C5 Corvette off for a while after driving, it will not start. I get the Engine light on but when I turn the key to start all lights turn off and it does not crank. If I pull fuse 9 (BCM A) on the IP fuse box it will start again.

Any ideas?

I did recently change out all ignition cables and now I get high misfire counts in Torque test results (TID:$0c CID:$20 and TID: $0c CID:$30, all above 64,208 count, max is 234 for each). Bad ignition wire connections? Could this cause the BCM to refuse to allow the engine to start? I get no other ECU code or DTC codes.

Thanks.




Note: I do not recall seeing any of these test codes occurring before changing out the ignition cables.

 

This has happened to a few C5 owners and here is a very good post that describes what it is and how to overcome it: Its a BCM WAKE/SLEEP issue.

 

I couldn't get the post to cut and paste into the reply. Damn Forum! (*^*&%

Provide an e-mail and I will send it to you

 

When ever you disconnect and reconnect the battery, the BCM/PCm and other modules can and will throw random DTCs Just clear them and monitor.

BC

 

- BCM Wake/Sleep Issue: http://forums.corvetteforum.com/c5-t...ol-module.html http://forums.corvetteforum.com/c5-t...tible-bcm.html



HA!!!! Fixed it.. Check out this post.

 

I am not sure if my issue is a "no-wake-up BCM" problem. I do get interior lights upon entry and trunk hatch release works with the key fob.

The only symptom is that it will not crank. Removing and then replacing IP fuse #9 allows it to crank. I will re-check the TDR.

Update: TDR is good. Engine has cranked and started several times since, including overnight. Testing ignition wires to see if there is a bad connection, high resistance, or moisture.

 

Unfortunately, it will not crank or start again. :-( So this issue is intermittent.

DTC shows "A6-SCM NO COMM." and if I try a couple times more to get the DTCs, it shows 5 codes for A6-SCM:
B2605 Seat Front Vertical Position Sensor Failure
U1255 Serial Data Line Malfunction
U1016 Loss of Communications with PCM
U1160 Loss of Communications with LDCM
U1064 Loss of Communications with BCM

I do not get any other codes in the other categories.

So, It seems like bad comms/serial data issues. Could this be a symptom of the "Wake/Sleep" issue? Or is this just some bad connections somewhere? The trunk hatch release on the fob still works and the interior lights do light up on entry. Basically, I see no other symptoms besides these codes and the fact the engine will not crank/start. I have not reset the BCM.

Any thoughts?

Thanks.

Update: I created a switch for fuse #9 by taking a blown 10A fuse and soldering on some leads then adding some terminals to allow attachment of good 10A fuse and toggle switch. So, if I encounter this situation again I can toggle the switch for a moment to disconnect the circuit and then turn it back on. I'll post an update if this works and/or if I find I have to use this on fuse #25 instead. I am guessing that fuse #9 is a low power circuit for the BCM where #25 (and #22 and #23) may be higher power since they are labeled as related to ignition. The couple of times this "no crank" condition occurred, pulling #9 did the trick so I assume it is okay to use it for the "wake" trick. Note: I am able to start my C5 even with this toggled on (closed) or off (open). So I am not sure exactly what fuse #9 controls. But it does "wake" the BCM upon removal/reinsert.

Update #2: Toggling IP fuse #9 did not seem to work. So I connected the switch to IP fuse #25. It worked at first but subsequent times when the car would not start it did not work. If I waited a while (10 or 15 seconds between crank attempts) it did start again. So this may not be a sleep issue but some other intermittent problem. Maybe a bad solder connection on the BCM or a bad connection somewhere? I reset the DTC codes and will wait for another non-crank condition to see what new codes are thrown.

Update #3: The issue returned after a few weeks. Toggling fuse #25 had no effect. Wiggling connectors on BCM enabled it to start again.
Codes were:
U1096 Loss of Communications with IPC
U1064 Loss of Communications with BCM
U1016 Loss of Communications with PCM