hey guys. i took my engine apart for about the millionth time, this time to put chrome valve covers on. when i put it back together, the car started and shut off right away. then i got it starteda nd the rpm started going up and down and had a hesitation when throttle was applied. i put some tools away and then took it for a ride when it started idling correctly and it had no hesitation but i was still gettign code 15. can anyone help e fix it?

 

That's your coolant sensor. Have you reset the codes yet? If not disconnect the ground batt cable and reconnect. Then drive it and see if the light comes on. If it does then check the coolant sensor (near the TB) and check the circuit. A remote possibility is your ECM, but that's not likely. Unfortunately I can't give you the entire diagnositic chart.

 

coolent sensor can set also when no coolent is actually touching it. Dunno how, but it did on the s10

Also, i know I have forgotten to hook it up few times. happens to best of us.

 

yea, i forgot to hook it up, but then hooked it up, reset the computer and whatnot but it still does it when i stop at a stop sign or somehting like that, any other ideas?

 

I have the GM service manual diagnostic chart here. It says a code 15 will set if the signal voltage indicates a coolant temperature less than -44 C or -47 F for 3 seconds. Now if you have a digital volt meter pull it out and check the resistance at the sensor. Here is a chart to help you:

210 F 185 OHMS
160 F 450 OHMS
100 F 1800 OHMS
70 F 3400 OHMS
40 F 7500 OHMS
20 F 13500 OHMS
0 F 25000 OHMS
-40 F 100700 OHMS

I am thinking more than likely you have a faulty coolant temperature sensor. The part number for my sensor on my 88 Camaro was #12146312 and it was less than $6 from GMpartsdirect.com when I bought it. You might want to double check on that number if you get it from there.