1989 chevy coolant sensor code 15 keeps showing up

[gmc 2500 4x4]

i replaced coolant sensor last year because code 15 showed up, and checked ground and its good. ran good and this year its showing code 15 again. faulty sensor? originally grounded at therm housing, i moved it to ground at ac bracket.could a stuck thermestat be it? any help here, thanx

[ChevyTech]

Look at the connector.

Code 15 will set if connection to the sensor is lost.

Here are specifications for testing the sensor if you have an ohm meter.
http://67-72chevytrucks.com/vboard/s...25&postcount=7

[gmc 2500 4x4]

i will try this, i did some reading and is leading me to think its the stat stuck open. as it does not go to high idle when started cold.

[ChevyTech]

A bad thermostat will not set a code 15 on this system.

Your 1989 is a OBD1 system that is very limited.

If the system has a code 15 set, it will substitute a value for that sensor. Fix the code before you worry about if it has a IAC problem affecting the cold idle speed.

[gmc 2500 4x4]

thanx for the info, i have read your many posts and you all are very helpful! im 2 the point where i get my '69 pickup 2gether i'll drive it and not worry bout sensors! lol

[ChevyTech]

You're welcome, and thank you for the complement.

Yes your TBI system has a few sensors, but of all the fuel injection systems it is the easiest to diagnose and work on, except for not having a fuel pressure test port.