GM 48 Misfire Diagnosis
How to read it
Code 48 reads as 4 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 48 mean?
Misfire Diagnosis
Common causes of 48
- Worn spark plugs or plug wires
- Failed ignition coil or module
- Vacuum leak or lean mixture causing misfire
- Low compression on one or more cylinders
How to fix 48
- Read the code with a scan tool and note which cylinder is flagged if shown
- Inspect plugs wires and coils before replacing parts
- Check fuel pressure and intake for leaks
- Run a compression test if ignition and fuel test good
- Clear the code and road test to confirm the misfire is gone
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.
Last updated 2026-09-19.
Report a correction for 48. Include your vehicle, the issue and a source if you have one.