Hello,

I have a 1999 targa with 145,000 miles

I recently rebuilt the motor and when I was installing everything I made a stupid mistake a placed the ground wire that susposted to go onto the passenger side block onto the ground post of the starter...

Now im having all sort of eltrical issues such as:
The cooling fans run at max until I turn the key to the on position
The temp gauge is pegged
Fuel gauge is at empty even though I know there is fuel
The car will crank but won't start im not sure if it's getting fuel or gas
windows wont go down
hvac has a mind of its own
ect

I cleaned my engine bay grounds, the car has a new battery and i confirmed its fully charged. I have a spare PCM so I swapped that since it's not too hard to do, that didn't help either. After that I pulled codes and that's when I noticed every signal modual says no comms.

I've tried to done research but im pretty stumpted eltrical issues are not my strong suit. Its been a very long year of car issues and getting my vette back up and running was what I was looking forward to but I messed that up, whoops.

Anyways any help would be appricated

 

Sounds like a serial data bus issue…you can follow this procedure if you have some basic electrical skills and a scan tool that can communicate with all of the cars module…if this is over your head seek out an auto electric shop…if they are unfamiliar with communication issues they can use this guide.


https://www.youtube.com/live/f_NEEdg...aNEwcygm7s8nnY




1) Locate the 2 Star Connectors to the left of the BCM and remove the buss bar or “comb” from star connector #2…it has 4 wires on it…see if the car starts…if no start go to next step.

2) Now remove the comb off the other star connector leaving both combs removed…make a jumper wire and jumper the BCM to PCM…light green to dark green wire….if car starts you have a module other than the BCM and PCM on star connector #1 pulling the data bus down….if car still doesn’t start the module pulling the bus down is either the BCM or PCM…go to next step.

3) Take your jumper wire and connect from the purple wire (data bus wire) to the PCM (dark green wire)…now with your scan tool see if you can communicate with the PCM…if you can now communicate the PCM is good and issue may be the BCM…to see if the BCM is indeed bad take the jumper wire and connect the jumper now to the BCM (light green)…with a scan tool that can communicate with ALL modules (NOT a code reader) and if you can’t communicate we can “assume” BCM is bad…for single module “no comm” you want to check the powers and grounds to that module.

 

I followed the steps and had no luck, I could not get my gm tech 2 to connect to the pcm or bcm. I will order a replacement bcm. What should I know about installing it?

 

Plot twist I re ran all the steps and I was able to communicate with the bcm here are the codes listed:
B0432
B0503
BO508
B2587
B2592
B2597
B2723
B3091
U1096
U1255

 

@C5 Diag

With the codes listed above is it still safe to assume the BCM is bad and needs to be replaced ?

 

You can’t comm with PCM and BCM ??…find that strange !!…If a module were bad you would see a “U” or communication code…U1096 is lost comm with IPC and 1255 is a “Serial Data Malfunction”…the data line usually gets shorted to power or ground…when you remove both “combs” you isolate all the modules…to start the car the PCM and BCM must communicate with each other…so you jumped the data line to the PCM and BCM
to see if the scan tool can communicate with it ??…if you can look at live data with the Tech 2 that tells me that you can communicate with that module…if you took a DVOM and probed pin 2 which is the data line you would see the voltage fluctuate between .2 to .7 or so with the key on…as mentioned in the video you would see a 0-7 volt square wave with a scope…when you “jump” the purple data line to the PCM and then BCM you are connecting the Tech 2 to each of those modules…you may not understand the concept of data communication.

 

 

 

@C5 Diag Sorry for the delay. I finally had a moment to troubleshoot the issue as the videos instructed, I tested each module separately. I had communications with all the modules but the PCM. I unplugged the PCM, reconnected the data link combs and all the modules communicated apart from the PCM. I plugged in my spare PCM and all the modules crashed. If I am understanding correctly, there has to be a wiring issue somewhere going to or from the PCM. Is there a common wire or wires that fail when someone wires the starter incorrectly that I should check first? Or really do you have any tips at all on how to go about finding what is causing the modules to crash when I plug in either of my PCMs.

Thank you for all your help it was been a godsend.

 

Without comm to the PCM I would first check the 2 fuses below for your ‘99…next disconnect the PCM connectors and with an incandescent 12 volt test light (not an LED) test the 3 battery and ignition feeds at the C1 Connector
and the 4 grounds on C1 (40,1) and C2 (40,1)….connect test light to B+ to check the grounds…if test light illuminates brightly ground is good…I like to use test lights on varying wattage to check grounds based on the current of the circuit tested which is shown below…I would check G106 which is above the starter where the negative battery terminal also connects to…if a module is missing power or ground that power or ground can “backfeed” onto the serial data line…you can start there.

 

 

All good things to check. I will add checking the serial data line itself between the PCM connector and the star connector to make sure it is not shorted to ground.

 

@C5 Diag I confirmed that the fuses are good, I checked the power supply to the ecu that is good. I went to check the grounds and found that the grounds are getting power as well. I confirmed with a multimeter and test light that I am getting 12 volt power via all 4 ground pins. Maybe a ground got melted to a power supply line? My next thoughts are to pull the header and try to check all the wiring between the battery, pcm and g106. Is that the correct course of action?
Thanks!

 

Sorry but I’m not there to see how exactly you are checking the PCM powers and grounds but if they are all good sounds like you need a PCM…there is no need to check the wiring between the battery, PCM and G106…you have already checked that…if a ground gets “shorted” to a power wire as you said a fuse will blow.

 

Solved. Im an idiot and didn't recall that there are two ground wires going to ground G106 one of which is the PCM ground. I mistakenly had the PCM ground wired to the positive post on the starter... Not my proudest work, but hopefully this can help someone else one day who has this issue. @C5 Diag Thank you for your guidance and thank you to the other fellow who chimed in. After fixing that, I finally got to start the car with the freshly rebuilt motor Then shortly after the rad cracked and needs to be replaced but hey that's life.

 

If you checked the PCM grounds with a test light if that is what you used and the PCM ground was mistakenly attached to B+ the test light would not have illuminated when testing and when you said " the grounds are getting power as well"....don't know if that meant that the test light was getting power ??

 

I replaced my headers and midpipe yesterday and had to remove my starter wires for them to fit through the bottom, when i finished i tried to start the car but it was only cranking and a lot of Non comm issues, same thing that happened to you, I can recall putting 4 wires in the starter positive post but didnt got time to check it, now that i know this imma give it a try, THANKS!