2001 Temp Gauge reading 100

I have a 2001 SE with a 3400. I was driving down the road when the temp gauge moved to 100 and the service engine soon light came on. Now when I start the car the gauges go through the test process, then the temp gauge moves to 100 and sets there. Everything else is running OK and the car has plenty of coolant.

Welcome to the forum. It sounds like you could possibly have a thermostat that's stuck open. If you know where the thermostat is at, it would be a good idea to pull it and make sure it's in good condition and isn't stuck open.

I ran the car in the garage for awhile. So I'm assuming the car was up to operating temperature. I also checked the resistance on the coolant sensor and it was at 2k ohms cool, 400 ohms at operating temp.

Further, I placed a 47 ohm resistor across the sensor plug and still read 100.

OK, I replaced the coolant temp sending unit and after driving the car for about 10 minutes the temp gauge started working. But the service engine soon light is still on. I tried removing the negitive battery cable to clear the error code, but no luck.

Is there something special about clearing error codes on these car??

OK, after many months of driving with a check engine light (shame on me) I replaced the thermostat. That seems to have fixed this problem.

I would like to add that this is the most difficult thermostat I have ever seen to replace. I can replace most thermostats in under 10 minutes. This thing took over 2 1/2 hours! I did manage to not remove the exhaust crossover but this is a royal pain. If anyone is looking to buy a car with a 3400, beware this engine is a pain to work on!!

OK, after many months of driving with a check engine light (shame on me) I replaced the thermostat. That seems to have fixed this problem.

I would like to add that this is the most difficult thermostat I have ever seen to replace. I can replace most thermostats in under 10 minutes. This thing took over 2 1/2 hours! I did manage to not remove the exhaust crossover but this is a royal pain. If anyone is looking to buy a car with a 3400, beware this engine is a pain to work on!!

the 2.4L ain't much easier, try changing a serpentene belt on one once, 4 hands required.