OBD-I Codes List

GM 98 Invalid PCM Program

Make
GM (1982-1995)
Category
Powertrain - Computer and Auxiliary Controls
Severity
Check Engine Light

How to read it

Code 98 reads as 9 flashes, pause, 8 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.

New to flash codes? The How to Read GM OBD-I Codes with a Paperclip walks through the test and what the numbers mean. The general OBD-I guide covers the rest.

What does GM code 98 mean?

Invalid PCM Program

Common causes of 98

  • MEMCAL calibration chip not matched to the vehicle VIN and drivetrain
  • MEMCAL not fully seated in its PCM socket
  • Corrupted PCM memory or failed programmable read only memory
  • PCM swapped in from another vehicle without the correct program

How to fix 98

  1. Read stored codes through the ALDL connector with a scan tool
  2. With power off, pull the PCM cover and reseat the MEMCAL in its socket
  3. Compare the MEMCAL part number to the VIN and drivetrain on the SPID label
  4. Inspect the PCM connectors and MEMCAL socket pins for corrosion
  5. Fit the correct MEMCAL or reflash the PCM to match the vehicle

Source

Qualified source review

Sources and review

Review: qualified. Read the source limits below.

  • GM OBD1 trouble codes, model and year page

    live reference page (troublecodes.net)

    Supports: code identity and GM meaning

    Fetched directly from the linked model page. Single publisher, so the record is qualified, not verified.

    https://www.troublecodes.net/GM/90_453/

Last updated 2026-10-10.

Report a correction for 98. Include your vehicle, the issue and a source if you have one.

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