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So I just finished a head gasket on my 2002 c5z... double checked the grounds, they’re good.. I believe my battery is bad, could that cause this? Even while being hooked up to another running vehicle and showing 13.8v?
Tried to pull the codes and I’m getting “no comm.” from everything! On top of that the fuel pump is not priming.
Last edited by Cory51191; Mar 17, 2020 at 06:09 PM.
Are you using a scan tool ??...usually if you can’t communicate with ANY module this is most likely a serial data bus issue...a single wire that allows all of the cars modules to communicate between each and will allow the car to start and run...all of those serial data wires from each module come together at 2 splice packs near the BCM...if that one module wire gets shorted to ground or power you get all “no comms”...watch this video and in this case it was a “start and stall” and the seat control module was bad and shorted to power !!...have you added ANY aftermarket equipment to the cars electrical system during this head gasket repair ???
On top of the other stuff, the ignition relay is buzzing really loud, check engine light is very dim, service vehicle soon, reduced engine power, low fuel, and the check gauges light stays on.
the PCM, BCM, and TAC module have all recently been replaced... had a tune done.. no issues... just did the head gasket - the battery has been disconnected for a couple of weeks.
Are you using a scan tool ??...usually if you can’t communicate with ANY module this is most likely a serial data bus issue...a single wire that allows all of the cars modules to communicate between each and will allow the car to start and run...all of those serial data wires from each module come together at 2 splice packs near the BCM...if that one module wire gets shorted to ground or power you get all “no comms”...watch this video and in this case it was a “start and stall” and the seat control module was bad and shorted to power !!...have you added ANY aftermarket equipment to the cars electrical system during this head gasket repair ???
I had similar symptoms months ago and after replacing a couple of the computers it went away... I have a new SCM sitting in my truck, it’s been there for months because this issue went away. Maybe I’ll throw it in tomorrow and see if that was the issue.
If you have and know how to use a DVOM remove both of the splice pack “combs” as in the video and see if you have 12 volts or ground on any of those wires with key ON...the serial data wire is the purple wire on each splice pack...the other wires come from each module...how long since changing those modules has the car been running OK ??...an auto electric shop should be able to diagnose this !!...don’t know what else to tell you !!...a good serial data line puts out a 0-7 volt square wave...with a DVOM you will only see maybe .4 to .5 volts !!
As in the video find the splice pack with the 4 or 5 wires...remove the “buss bar” as in the video and see what happens...the other splice pack has the serial data wires for the BCM and PCM and more modules...remove that one and see what happens...the car will not start unless you jumper the BCM and PCM data lines together...they are the light and dark green wires !!
Well... I found the issue. It was a ground on the passenger side. The eye broke off. I soldered a new wire in place and put a new eye on it. It was the ground from my recent thread.
I’m not sure which one it is. It doesn’t quite reach the engine block grounding location so I connected it to the stud on the frame, where the battery and three other grounds are.
No comm to anything
