Appears my cooling fan recently stop working except when AC turned ON, so at least both fan motors seem to be in working order. I found two thermal sensors attached to the engine, first - single wire and second - two wire design. Please advice steps to troubleshoot.
Cooling fan won’t come on
- Thread starter den_s
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What kind of GM car is it?
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Most likely, the single wire sensor is for the gauge, and the 2 wire for the ECM.
That is, unless the single wire sensor is a switch for the fan relay. Follow its wire.
Ohm the single wire sensor, there should be some ohms between its prong and ground. Infinite ohms indicates:
1) You've found the fan switch, now replace it
2) You've found a varistor that's no good, replace it.
The two pin one you can check the ohms between pins then look them up on a chart on the web somewhere. Do it after the car's sat overnight so it'll be ambient temp. Most of these things have the same temp/ohms gradient, make independent.
Also you can take the wire to the single-pin thing, turn the key to "run" but don't start the car, and ground this wire. If the fan comes on, there was your fan switch. If your dash gauge goes full hot, it's your gauge sender. Don't leave it grounded too long, could be bad for the gauge.
That is, unless the single wire sensor is a switch for the fan relay. Follow its wire.
Ohm the single wire sensor, there should be some ohms between its prong and ground. Infinite ohms indicates:
1) You've found the fan switch, now replace it
2) You've found a varistor that's no good, replace it.
The two pin one you can check the ohms between pins then look them up on a chart on the web somewhere. Do it after the car's sat overnight so it'll be ambient temp. Most of these things have the same temp/ohms gradient, make independent.
Also you can take the wire to the single-pin thing, turn the key to "run" but don't start the car, and ground this wire. If the fan comes on, there was your fan switch. If your dash gauge goes full hot, it's your gauge sender. Don't leave it grounded too long, could be bad for the gauge.
How do you know the fans stopped working? Typically except for A/C they'll only come on when coolant temp exiting engine reaches like 202 deg. F or even higher on newer models. If the sensor were dead open or shorted I'd imagine you'd get a check engine light. Otherwise if it's just grossly inaccurate or whatever it could cause mileage and hot start issues and of course the fans not coming on.
Single wire sensor kicks the fans on when the engine reach's max temp. the coolant heat opens a bi metal strip in the sensor causing the sensor to send a ground signal to the fan motors thus turning the fans on.Unplug the plug from the sensor & run a grounded piece of wire to the sensor plug, if the fans turn on..replace the sensor....make sure the ignition key is on.
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