I have a 2003 ,C5 that won't start. If I momentarily disconnect the battery ground wire, then reattach it, the engine will crank and run for a few seconds. My fuel tank is full, but the gauge shows empty. Also my power windows and door locks won't work.
Hopefully someone can give me some ideas as to what's causing this and what I need to do to get the car running again.

 

Sounds like the “classic” serial data network issue !!...does the oil pressure also show zero and water temp also max out ??... do you see all the DIC warnings scroll through...reduced engine power, service vehicle soon, low fuel ??...I can show you what to test with a voltmeter on the DLC (where a scan tool attaches to) for a short to power or to ground on the serial data line but for now just find the 2 “Star Connectors” by the BCM...one has 4 wires I believe and the other has 9...there is a shorting bar or “comb” on the top of each...squeeze the top of the one with 4 wires off and now see if the car starts...make sure the comb is clean with no corrosion...I helped someone 2 weeks ago with this same problem...we took sandpaper and cleaned the comb...that’s all the problem was !!...clean it good !!...his comb looked OK visually but it took us a while to figure it out !!...we could only get a few modules to come back online but not some others... if that doesn’t work pop the comb off the other one....clean that comb and reinstall it...see if the car starts...if no pull the comb back off again...to allow the car to start with both combs removed you will need to jump the PCM and BCM modules to each other...the light green and dark green wires together !!...with a scan tool if you have one I can explain how to check which of the 12 computer modules are not communicating !!...what happens is either a module loses either a ground or power internally and the power or ground back feeds to that data line....modules can’t talk and car won’t start !!...we will then check each wire at the star connector for either 12 volts or ground on the data wire... it’s normally a 0-7 volt square wave !!
PS..a lot of times the seat control module under the seat gets wet (passenger side is a relay control unit) and messes up that module as in the video or the door modules !!

 

I don't know about the oil pressure and water temperature dials, but the DIC does cycle through all of those messages.
Last year I had a problem with water coming into the passenger side floor. Somehow the cowl drain became clogged.
I'll check out what you told me, tomorrow. I'm hoping that it is only the four wire comb being corroded. I will let you know.

Thanks for such a quick response!

 

Don't know if you have a multi meter but when you pop off the "comb" on Star Connector #2 (4 wire) see if you either have 12 volt power or ground on any wire denoting your "problem" module.... you won't see a 0-7 volt signal unless you have a graphing multi meter or a scope...you'll see the voltage fluxuate between .40-.49 or so with a multimeter if it's a good data signal...you should see this on the purple wire !!...the pics are what you will see on the IPC !!

 

Had weird messages on DIC and a persistant P1518 DTC code. Replaced TAC and no change. Finally bit the bullet and took out console and dash panels and replaced Ignition Switch. Started right up.
Low voltage from bad contacts can cause weird problems. Might be something else but Ignition Switch can cause many symptoms.

 

C5 Diag
I pulled the comb out of the 4 wire assembly. My car started instantly. I checked the comb and there was very minimal corrosion. I then pulled the comb on the 9 wire assembly and noticed the same thing. I pulled at a fine nail file and removed all of the corrosion on both combs and reinstalled them.
With both combs reinstalled, my car wouldn't start. Now I need to find my multimeter and check out that purple wire.

 

The issue is on the 4 wire Connector...you'll probably find 12 volts or ground on either the seat module or the 2 door modules data wires !!....you're almost home !!...on the purple data wire you'll see the voltage fluctuate around .4 volts or so...the other wires is where you'll see either the 12 volts or short to ground...the seat control module is brown/white, the driver door module is brown, and the passenger door module is tan !!

 

I'm getting a fluctuation between .16 and .37 volts on the purple wire. What's next?

 

That's normal !!...you are reading the data network which is really a 0-7 volt square wave...you won't see that with a multi meter...now probe the other 3 wires and see if you have either 12 volts or ground (near 0) on each one !!

 

C5 Diag,
I got to some brighter light and saw that there was still a little bit of corrosion on the pin for the purple wire. I removed it and things are fine!

Thank you very much for your help
Pat Hillyard
NCM Ambassador from the Corvette Club of Western Pennsylvania

 

Hi Pat !!
SUPER !!...BTW,they make terminal cleaners for that sort of thing...they are good to have for any connector that you might have to remove to clean up corrosion like that....also I recommend a product called Stabilant 22...it's a little expensive about $50.00 but you just need a drop or less on each pin and never worry again...Deoxit Gold is good too !!

 

C5 Diag
The car starts fantastically, but my power windows and door locks don't.
I'm getting 12.5 volts on the black and white wire and I'm getting 0.05 volts on the tan and brown wires. Does that sound normal?

 

Well I''ll be dipped !!...Do you mean the BROWN/BLACK wire on Pin K ??...should be at the opposite end of the purple wire...SHOULD NOT HAVE 12 VOLTS ON THAT !!...That wire is shorted to power !!...the brown/white is the seat control module (SCM)...there is the SCM which is under the drivers seat and a seat relay control under the passenger seat...Pull out the driver seat and unplug the seat control module...that DEFINITELY has the brown/white data wire on it...try that and let me know what happens...you sure the carpeting under the drivers seat was not affected by the water ??...thanks !!

EDIT: the driver SCM is powered by a fuse a..fuse is SCM-L fuse 4 and also a breaker #35 (20 amp)....called PWR ST/DRV. Pull them and see what happens before pulling the seats !!....both are in the IP fuse box.

 

C5Diag
I'm sorry. I'm color blind. I have the purple wire on one end. Next to it is the dark brown wire, where I'm getting 0.05 volts. Next to that wire is the tan wire with the same voltage as the dark brown wire. On the far end of the connector is the white/ dark brown wire, where I'm getting 12 volts.
The driver's side floor never got wet. So should I remove the passenger side or the driver's side seat.

 

Read my post #13 above...brown/white is drivers SCM !!...I'll be leaving work at 6:30...PM me your Cell if you rather just discuss this quickly !!...in the video the SCM was de pinned and then they were able to get the window to work !!

 

C5Diag
Where is the IP fuse box?

 

At the passenger footwell to the right of the BCM !!...on the right of the footwell...black box !!...unscrew it and pull the top cover off

 

C5Diag
Ok. Now that I know where it is located, I'll check the fuse and circuit breaker.

 

Remove them and see if windows and locks now work !!...should de power the seat control module !!

 

C5Diag
I was wrong. I felt under the driver's seat and felt some dampness. I know that last year, there was dampness under the passenger seat. Both power seats work. What should I do next, pull the driver's seat or the passenger seat or pull both?