What causes GM code 99?

Wrong MEMCAL or flash program for the vehicle Loose MEMCAL in the PCM Corrupted PCM memory PCM replaced without correct programming

How do I fix GM code 99?

Read codes with an ALDL scan tool Reseat the MEMCAL with power off Verify part numbers match the VIN and drivetrain Inspect PCM connectors for corrosion Install the correct MEMCAL or reflash as fitted Replace the PCM only after programming is verified

99 Invalid PCM Program

Q: What does GM code 99 mean?

GM code 99 — Invalid PCM Program. Applies to 1993-1995 Camaro, Corvette, C/K trucks, Caprice.

Make: GM (1982-1995)
Category: Powertrain - Computer and Auxiliary Controls
Severity: Check Engine Light
Applies to: 1993-1995 Camaro, Corvette, C/K trucks, Caprice

How to read it

Code 99 reads as 9 flashes, pause, 9 flashes on the check-engine light. Jump terminals A and B on the ALDL connector with the key off, then turn the key on with the engine off and count the check-engine flashes.

What does GM code 99 mean?

99 — Invalid PCM Program. This code sets when your vehicle computer detects invalid pcm program.

Common causes of 99

Wrong MEMCAL or flash program for the vehicle
Loose MEMCAL in the PCM
Corrupted PCM memory
PCM replaced without correct programming

How to fix 99

Read codes with an ALDL scan tool
Reseat the MEMCAL with power off
Verify part numbers match the VIN and drivetrain
Inspect PCM connectors for corrosion
Install the correct MEMCAL or reflash as fitted
Replace the PCM only after programming is verified