What does it mean if the 'service engine soon' light intermittently comes on accompanied by rough shifting on a 1994 GMC Suburban K1500?

Answer 1

Sometimes when the "Service Engine Soon" light comes on, depending on the problem the computer will go into "Limp Mode" which are factory settings for different sensors. This also changes your shift settings. Limp Mode will allow the vehicle to continue on its way but will run bad enough to make you get it fixed. The trouble codes should be stored. When retrieved may lead you to the main problem. When problem is fixed clear all trouble codes. ______________________________________________________ Update 7/7/08: I'd also suggest getting your transmission looked at. Sometimes when the "Service Engine Soon" light comes on and you feel a difference in how the transmission is shifting it can mean that the computer is detecting slippage in the tranny. It will then crank up oil pressure in response to this. In doing so, the engine can sometimes shift "hard" (thats how my wife described it) which can cause problems in your transmission such as breaking the shell around the gears. If you do get it checked & cleared make sure you right down the codes in case you go you have to get work done later. An experienced mechanic will know if what he is fixing is the problem or the symptom based on error codes. If you don't you could end up fixing the same thing twice.