GM 51 PROM Error
How to read it
Code 51 reads as 5 flashes, pause, 1 flash 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 51 mean?
PROM Error
Common causes of 51
- Loose or corroded PROM or MEM CAL in the ECM socket
- Incorrect MEM CAL for the vehicle
- Bent PROM pins from prior service
- Failing ECM socket or internal fault
How to fix 51
- Turn the key off and reseat the PROM or MEM CAL carefully
- Inspect pins for bends and corrosion and clean contacts
- Verify the MEM CAL part number matches the vehicle calibration
- Clear codes by disconnecting battery power and recheck
- Replace the MEM CAL or ECM only after seating and part number check good
Sources and review
Review: qualified. Read the source limits below.
- GM and Chevrolet OBD1 Trouble Codes (ALDL Fault Code List)
live reference page (troublecodes.net)
Supports: code identity and GM meaning
Fetched directly. Single publisher, so the record is qualified, not verified. Causes and check order are curator-written from the circuit the code names.
Last updated 2026-09-19.
Report a correction for 51. Include your vehicle, the issue and a source if you have one.