Replaced PCM

[5996SUBURBAN]

I have a 1999 GMC Yukon that I bought a PCM out of a salvage yard for itand now the security light comes on and will not let the vehicle run. It does the whole start and die thing. The computors have the same service code and I even swapped the PROM's out but still security will not let us run. Do I have to have the computor refashed or not.

[GM-Tech]

I don't know how you swapped the PROM since these don't have one. Perhaps it's the type with knock sensor chip.

 

In any case, even if it's the same part number, the calibration within can be different. But the big problem is that the security system is not recognized and a "theft relearn" has to be done. This can be done manually by you, but don't know if other factors will keep it from running without reprogramming it. Here's how you do the theft relearn...

 

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PASSLOCK Reprogramming Auto Learn

Conditions

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 VCM/PCM

 

The EVO/Passlock™ module will set the DTC B3031 module in the learn mode when entering the reprogramming procedure.

 

Steps

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:

 

 

• For 5.0/5.7L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0/5.7L

 

• For 6.5L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 6.5L

 

• For 7.4L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 7.4L

 

 

The following is the Auto Learn Procedure:

 

Insure the ignition key is in the ON position.

Clear all EVO/passlock™ module and VCM/PCM DTCs. Record and refer any VCM/PCM DTCs to:

- For 5.0/5.7L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 5.0/5.7L

 

- For 6.5L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 6.5L

 

- For 7.4L engines, refer to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls - 7.4L

 

Momentarily rotate the ignition key to the CRANK position (Do NOT start the vehicle), then release it to the RUN position (Do NOT 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 if 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).