Service Engine Light

[martym]

I have a 1994 GMC with an 6.5 / turbo the engine runs fine except when towing and under a heavy load the service engine light turns on. After I lift my foot off the throttle the light go's off .

 

Any suggestions on whats going on would be appreciated.

 

 

Marty

[Zembonez]

Possibly a trans or exhaust overheating issue? I'm sure somebody else will chime in here.

[svensk]

Only way to know is to go get the code read.