GM 79 Transmission Fluid Over Temp
How to read it
Code 79 reads as 7 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.
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 79 mean?
Transmission Fluid Over Temp
Common causes of 79
- Heavy towing or hot weather with low airflow
- Low or burnt trans fluid
- Blocked cooler lines or cooler
- Slipping clutch packs heating the fluid
How to fix 79
- Read codes with an ALDL scan tool and check fluid level first
- Inspect fluid color and smell for burn
- Check cooler lines for kinks and the cooler for debris
- Let the trans cool, clear the code and retest
- Flush the cooler and service fluid if overheated
- Diagnose slip or cooler flow if the code returns fast
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 79. Include your vehicle, the issue and a source if you have one.