HELP!!! Engine Temp Gauge

[01scolmoo]

I have been having issues with my 01 GA SE1. My engine temp gauge randomly stops working. It seems to happen most often when I am driving long distances, such as on the freeway. It will just drop to 100. When I start the car the gauge goes up to 100 but wont move past it. Thinking it was the most obvious, I replaced the temp sensor on the engine. However it still wont work. I checked the connection to the sensor and it was reading 10v instead of the 5v my haynes manual said it should be. But I may not be using the voltmeter correctly. Yesterday I was driving around and the sensor just started working again but then today on my way to work it quit again. Whenever it quits working the fans stay on too. I took it to autozone to check the engine codes and they said (I didn't get the codes) that it was a repeating code that signals that the coolant temperature was not sufficent enough to allow oopperation of the thermostat. I don't see how the thermostat not working or being stuck open would cause my temp sensor to quit working? Any ideas? Thanks

[rixGAphx]

'01 V6; 7-yrs old, so mebbe 85k miles?
You're somewhere in TX; might be in an area with mild winter temps, might be getting blizzard conditions, we don't know.

You may have the wrong sensor installed; but that doesn't explain why it behaved this same way prior to swapping sensors.

On the 4-cyl engines, there are 2 coolant sensors:
* One at 12V operating the gage only, just like the dash gage in a '57 Chevy or such;
* The other is at computer-operating voltage, about 5V, and it reports coolant temp ONLY to the PCM for it to use in determining FI and other engine-operating parameters.

On the GA V6, there is only one Engine Coolant Temp sensor, and it receives ONLY 5V from the 'puter (PCM) and reports data back ONLY to it.
* The PCM uses the data for FI and operating parameters; AND,
* Sends a 5V signal to the Instrument Panel Cluster (IPC) which has its own microprocessor that converts the data into usable electricity to move the gage needle.
Sometimes on the V6, temperature gage problems are only in the IPC, which would need replacement (can't be repaired).
But your PCM codes (as read by AutoZone; wish we had the actually code :( ) indicate the problem is downstream, toward the PCM and/or sensor.

Your reading of 10V was impossible, since the 'puter only allows 5V out; unless a previous owner completely f'ed-up the wiring or there's a short-circuit to the sensor.
Did you measure current-to-ground? That's wrong, since the sensor doesn't 'go to ground'; it receives 5V power from the same wire that supplies most other engine sensors, then modifies that voltage (via its variable internal resistance) and sends the data back to the PCM.

The PCM reads the data, and compares it to preset tables that say what it (the PCM) should *expect* to see.
It *should* see the coolant temperature rise within 4-6 minutes of the engine starting.
If it doesn't *see* this (on the data from the ECT sesnor), then it thinks, "Something's screwed-up; I'ma gonna protect my owner's engine by turning the fans on full-time, and I'ma gonna set a code telling my owner to check the T-stat and other parts of the coolaing system."
The PCM doesn't know if the t-stat is stuck open, or if the sensor is faulty, or what's wrong; it just knows that a GM engineer, 7-years ago, programmed it to make a report when the data from the sensor indicates the engine isn't warming-up properly.

Personally,I *think* you may have a simple wiring problem in the sensor circuit;
Either somebody screwed with it and ran 12V directly to the sensor; or, there's a problem with the data wire connector from the sensor back to the PCM.
First step is always to disconnect/reconnet the sensor plugs, to make sure they're clear of foriegn matter.
Second step would be to check the wiring in the area where somebody might have been working (like installing a stereo under the dash) shortly before the problem was first noticed (this prolly doesn't apply in your case).

I don't have a wiring diagram for the '99+ GA's, so I can't help more about the wiring run back to the PCM.
Mebbe somebody else can chime-in.

Hope this helps,
-Rick

[01scolmoo]

thanks! I was reading some other threads and happended upon another one that had a similar problem. Theirs turned out to be the thermostat. So I'll try both and see where that gets me. Sorry to everyone that this problem is sort of a re-post. When searching previously I couldn't find any similar problems.:D