A friend of my cousin's 1999 Tahoe After replacing coil, ign module and pcm, what else would cause no spark? Before I got to it, he changed the coil, module, crankshaft position sensor and fuel pump. I verified all those items were working and tried a salvage yard PCM from a 98 Tahoe.
I wasn't aware of the need to match up the numbers on the PCMs. But with that PCM, I got spark and the truck would start then die as if it was just running on the fuel pump prime. I felt pretty certain that the proper PCM would solve the problem so I got another salvaged PCM with the proper number and tried it. No dice. No spark again. I took that one back and got another PCM and got the same result. No spark. I think I am missing something simple but am at a loss.
So we have intermintant no spark or just no spark at all?Any codes in the computer?Which engine does it have?
June, 8, 2012 AT 3:07 PM
No spark at all. The only time I got spark was with the first PCM with the wrong catch code or number. No codes were in the original PCM. Engine is a 5.7 gas.
June, 8, 2012 AT 3:23 PM
That likely wasn't just fuel pump prime. It was the security system locking you out. You can't simply install a used PCM as they are programmed to your specific car and VIN#. You can try a security relearn but you can still expect other issues with the wrong PCM.
PASSLOCK REPROGRAMMING AUTO LEARN
IMPORTANT: If a new vehicle/powertrain control module (VCM/PCM) is being installed for the first the manufacturing enable bit will be set and the auto learn procedure may not be necessary.
The following procedure allows for anyone to reprogram the EVO/PASSLOCK module learned data code with any tools, other than the scan tool, when any of the following parts are replaced: The EVO/PASSLOCK module
The PASSLOCK sensor
The EVO/PASSLOCK module will set the DTC B3031 module in the learn mode when entering the reprogramming procedure.
IMPORTANT: Erase the PASSLOCK related diagnostic trouble codes (DTCs) that are stored in the VCM/PCM. If there are any powertrain related DTCs, record these DTCs then: The following is the Auto Learn Procedure: Insure the ignition key is in the "ON" position.
Record an VCM/PCM DTCs and to refer to Powertrain On-Board Diagnostic (OBD) System Check. Clear all EVO/PASSLOCK module and VCM/PCM DTCs.
Momentarily rotate the ignition key to the "CRANK" position (DO NOT start the vehicle), then release it to the "RUN" position (DO NOT turn key "OFF" in the process).
Wait 10 minutes. Observe the "SECURITY" indicator. Refer to the following list for the appropriate responses: If the PASSLOCK sensor was replaced the "SECURITY" indicator will flash for the 10 minutes duration.
If the EVO/PASSLOCK module was replaced, the ""SECURITY"" indicator will flash for a few seconds and then remain "ON" for the remainder of the 10 minutes duration.
If the VCM/PCM was replaced with a new programmed VCM/PCM and connected to the vehicle for the first time, the vehicle will start and this procedure may not be necessary.
If the replacement VCM/PCM was connected to any vehicle at any other time, even momentarily, the "SECURITY" indicator will flash for a few seconds and then remain "ON" for the 10 minutes duration.
The "SECURITY" indicator will transition from flashing to "ON" briefly to "OFF" after 10 minutes of remaining in the ignition "ON" position.
Turn the ignition switch to the "OFF" position and wait for 10 seconds.
Repeat steps 3 - 6 two more times. The new security code is ready to be communicated among the PASSLOCK sensor, EVO/PASSLOCK module and VCM/PCM.
The new password is learned on the next ignition lock cylinder cycle from "OFF" to "CRANK" to "ON" (start attempt).
June, 8, 2012 AT 4:09 PM
Thanks for the assit wrenchtech let us know how the pass lock relearn works.
June, 8, 2012 AT 4:13 PM
So if I understand you correctly, installing PCM with the proper catch code from the same year and model will still give me no spark? Is the only option for a proper flash at the dealer? Also in the relearn procedure it states to momentarily rotate the key to crank. Would I, in order to perform that step, "bump" or engage the starter?
I reread your response and just to clarify, I currently have no spark. I only time I got spark with the PCM with the wrong catch code. When I replaced that PCM with one with the proper code, The no spark issue returned.
June, 8, 2012 AT 5:14 PM
The PCM has to be programmed or it just isn't going to work. The relearn would only help you in the start and stall symptom.
June, 8, 2012 AT 5:15 PM
Even when you get the correct, programmed PCM, you still will have to perform the security relearn.
June, 8, 2012 AT 5:39 PM
Ok. That's clear enough. Thanks for your assistance.