OBD-I Codes List

GM 55 ECM Error

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

How to read it

Code 55 reads as 5 flashes, pause, 5 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 55 mean?

ECM Error

Common causes of 55

  • Internal ECM analog to digital converter fault
  • Poor ECM power or ground connection
  • Voltage spike damage from charging system faults
  • On digital EGR models a solenoid 3 fault uses this same code

How to fix 55

  1. Check ECM powers and grounds including fusible links
  2. Verify charging voltage is not spiking before condemning the ECM
  3. Inspect the ECM connectors for corrosion and backed out pins
  4. On digital EGR models test the EGR solenoid 3 circuit as the alternate cause
  5. Replace the ECM with the correct service number and transfer the PROM and CALPAK

Source

Qualified source review

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.

    https://www.troublecodes.net/gm/

Last updated 2026-09-19.

Report a correction for 55. Include your vehicle, the issue and a source if you have one.

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