Having a problem with the check engine light coming on in my 03 1/2 ton. 4.8L engine. Taken it to the auto parts store and had the code read and cleared.

Came up with 2 codes, 1 for the thermostat, one for the temp sending unit. Had the guy clear it the first time, it's been close to a month, it came back on today. Weather conditions were similar both times (less than 50*, strong north wind of 20 or better). Both times I was driving right into the north wind. Is it possible for the light to come on if the thermostat is stuck OPEN? My gauge never moved and I watched for a solid 20 minutes on the rest of the drive home.

Probably going to replace my thermostat Saturday just to be safe, truck has 94,000 on it.

My big question is whether or not this will cure the problem. My logic is that if it was the sending unit causing the light, the temp gauge on the dash would not read AT ALL, so if I'm still getting a reading, it should just be the thermostat? If I'm incorrect please tell me otherwise.

Thanks for the help!

 

I'd change the thermostat, especially if it hasn't been for a long time. If it opens too soon the temperature will be lower than it should be.

 

What exactly were the codes and freeze frame data? If the ECT read something illogical like -40, the ECT sensor or circuit is open.