2002 Cavalier Temperature Gauge Not Working?
75

Asked by Mike May 04, 2013 at 02:53 AM about the 2002 Chevrolet Cavalier Sedan FWD

Question type: Maintenance & Repair

I originally had posted this: http://www.cargurus.com/Cars/Discussion-t2089_ds545431?
sntEmlId=42327096#msg242442

However, I finally bought an OBD ii code scanner, and got code P0118 for "Electronic
Coolant Temperature (ECT) sensor circuit high input"

I tried replacing the ECT sensor (the 2 wire one/black and yellow) on the upper radiator
hose going into the engine.  That didn't resolve the problem.

What I have figured out is that every time the relay and cooling fan kick in, the TRAC
OFF light comes on and no matter how many times I reset it at that point, it will keep
coming back on.  Obviously this makes for a bad drive, with really hard shifts, etc.

The temperature GAUGE, however, doesn't work at all.  It just sits below 0.  It randomly
would work sporadically, but now just constantly sits at 0.

I heard there's another sensor with a single wire that's specifically for the gauge.  Could
that one be causing this?  I don't know where it's located.

Any other ideas?

4 Answers
75

Mike answered 11 years ago

When I scan it when the TRAC OFF light is on, it's the same code, 0118, which is "Electronic Coolant Temperature (ECT) sensor circuit high input", no matter how many times I reset it, if that fan relay is on or kicks in, it comes on. When I first start the car, it isn't on until that relay kicks in. I also checked voltage on the harness, there is 5V. So since the gauge doesn't work, I'm guessing it has something to do with that, because everything works, sounds, and looks fine, and the fan obviously comes on, so it gets the reading from the ECT sensor on the coolant pipe. The gauge just doesn't work. People have said there's another sensor that is for the gauge that is elsewhere. Does anyone know where it is? There's the two wire one at the front by the alternator which is used by the computer for the relay, and supposedly there's another maybe single wire one that has to do with the gauge? Maybe that is shorting? I don't know where it is though.

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yetilikesbeer answered 11 years ago

The ECT (2-wire) signal is sent back to the PCM. The PCM uses the value for fuel calc's and to operate your fan. The A/C can also trigger the fan. Since that's code that it's spitting out I would test it again. With the 5V ref into the sensor piggyback to the output and verify that the reading starts at a certain value and changes smoothly as your engine warms up. Circuit high would make me think that the wires or switch were shorted together. Check continuity between the sensors pins. A low reading would indicate a short and high would be an open circuit. I think this are somewhere around 1000 ohms at room temp. Can't remember but I will check and get back to you. The single wire sensor only operates the gauge. They usually are threaded into the head and have a green pigtail 4" long to the engine harness. I will find it's location for you. Sometimes the pigtail or the harness touches the exhaust and melts. You are correct it will show zero when grounded. My 3.1/2.8 v-6's do this all the time. Check the wire. Tape it if the conductors are not broken and tie it out of the way. If the wires are good you may need a new sensor.

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Mike answered 11 years ago

This is a great detailed answer that addresses my exact concerns. If you could find the locations for me that would be amazing. I typically do all my own car work as I'm on a very tight budget. The cav has 161k, got me across the country and gets me to auditions. I'm not going to give up on her yet.

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yetilikesbeer answered 11 years ago

Ok your temp indicator is a pain. I'm at work for a few days so I have limited resources. I can't find a pic anywhere for yah. It's got me stumped, for now. Back to your ECT. I usually test mine in water, heat it and check with a voltmeter. 32 F would be 10000 ohms, 86 at 2200 ohms and 212 at 176 ohms. So as your resistance goes down you get closer to a short, which would be your 5V ref to the PCM. Circuit high input. It has to be the sensor or the wiring. Maybe inspect the plug. Hope it's not worse like a PCM issue. Can your scanner read live values? If read that a dead short is around 300 F. A $5 10k ohm potentiometer would allow you to test the circuit.

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