Pegged over 260, coolant temperature sensor not working properly

Tiny
AWARNER
  • MEMBER
  • 2002 PONTIAC GRAND PRIX
  • 3.1L
  • V6
  • 2WD
  • AUTOMATIC
  • 190,000 MILES
Where is the ground wire located at for the engine coolant temperature sensor? Ever since replacing the coolant temperature sensor with one I dropped and continued to install it. I then replaced it with a brand new one and my gauge on the dash is still pegged out past 260. What can I do to reset the gauge? The picture that is included is after the car has been sitting for over 3 hours.
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Sunday, August 22nd, 2021 AT 5:46 PM

3 Replies

Tiny
STEVE W.
  • EXPERT
What does the gauge do when you just turn the key on? It should cycle across the gauges and then stop. If the gauge isn't moving it isn't the sender or a bad ground, it would be a fault in the gauge or it's drive motor. If it does cycle but then returns to that position it could still be the stepper motor. A way to reset them involves gunning the gauge test function on a dealer level scan tool. However that just does the same thing as turning the key on. Please try that and report back and we have a starting point.
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Sunday, August 22nd, 2021 AT 11:35 PM
Tiny
AWARNER
  • MEMBER
If I go out after it sitting all night and just turn the key without cranking, it does start out on the cold side and cycles up past 260 just never comes back down unless I shut the car off. Crank it over and starts automatically goes past the 260. Just weird after installing a bad sensor it's stuck. Definitely making my car run rich though tank of gas is only getting me about 160 when b4 I could get up n sometimes over 310 miles.
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Monday, August 23rd, 2021 AT 1:45 AM
Tiny
STEVE W.
  • EXPERT
It sounds like it could be an open connection causing the issue. There are 3 wires for that sensor. One sends the signal to the gauge, another is the signal for the PCM and the third is the ground. The likely suspect would be a failed ground as it would cause a problem with both while a failed wire to each of the others would cause problems with just that item.
The ground signal is shared with the MAP sensor. To test it you can use a multi-meter set to ohms. Then look at the pin with the orange wire with black stripe. This is the shared sensor ground. Go to the MAP sensor and unplug it and test for continuity between the two orange w/black wires. Then check between them and a good ground. If you find no connection then it is likely that the connector or wire has failed. If you find a ground at the MAP but not the ECT then it is in the wire that goes between them. A quick test there would be to pierce the wire right at the back of the ECT connector and test for ground, then run a jumper from that to a good ground. If the gauge corrects itself with a cold engine and key on you need to repair the ground wire.

https://www.2carpros.com/articles/how-to-check-wiring
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Monday, August 23rd, 2021 AT 3:50 AM

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