What causes GM code 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 do I fix GM code 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

79 Transmission Fluid Over Temp

Q: What does GM code 79 mean?

GM code 79. Transmission Fluid Over Temp. Applies to 1991-1995 C/K trucks, Suburban, Yukon, Caprice.

Make: GM (1982-1995)
Category: Powertrain - Transmission
Severity: Check Engine Light
Applies to: 1991-1995 C/K trucks, Suburban, Yukon, Caprice

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.

What does GM code 79 mean?

79. Transmission Fluid Over Temp. This code sets when your vehicle computer detects 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