Check Engine Light Over 55 MPH
 

I have a 1991 full size Blazer, 4 inch lift, big tires..on the highway, once I hit 55 the check engine light comes on. I've had it since 2006, it runs really good, I take good care of it. TWO mechanics told me it was because of the after market tires. Can this be true? No codes come up, in town traffic (45 and under) no light comes on. I just worry something is being missed. Thank you, Stephanie

I would think if the light comes on there will be a code, or at least some freeze frame data to look at .....I really doubt aftermarket tires would cause a light unless the tires are different sizes from one to the other .

You have to let us know what the code is that is popping up. Being OBD1, you should be able to trigger the check engine light to blink out the codes by using a paperclip to jumper two terminals in the diagnostic port under the dash (google "GM OBD1 codes" and you should get the proper pins and procedure).

Let us know what code(s) it returns and we'll go from there.

*Moving to Full Size K5 Tech*

Hey there. I have the same issue (94 full size Blazer). After about 10 minutes at 80 km/h (I'm in Canada) the "service engine soon" light comes on. When I put code reader on it shows no codes. Light always goes out when truck gets shut off and restarted. I have regular tires on it. (265/75r16)

weird , now it has been alone time since i played with obd1 , can a person obtain any freeze frame data or do any live data tests with the old system ?