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2008 Chevy trailblazer 4.2.temp gauge quit working. Go to ipc with scan tool engine hot shows 95 degrees F. Go to pcm cts says 195 degrees F. Go to ipc functional tests command gauge on and all gauge go far right including the temp gauge. Bad ipc or wiring issue? Input problem? Any tests to isolate problem? I was thinking bad ipc. Any ideas. Thanks. Joe
Could be a substituted default value. Do a ressistance check on the temperature sensor. The sensor is a negative temperature coefficient thermistor.
Not sure about GM USA but with the plug disconnected the sensor will have generally have a resistance somewhere between 2,000 and 4,000 ohms depending on temperature. When the engine is hot the resistance will be much lower say 200 to 700 ohms.
The other test are to check the 5v supply to the sensor --- this is a special case of a 5v reference voltage. Measuring between this wire and a known good ground disconected ignition key on it should read close to 5v on a digital multimeter NB. if you use a Power Probe it is likely to be lower. You should also check the sensor ground plugged in ignition, by checking the voltage between the ground wire and a known good ground ie. cylinder block or battery negative.,
" We're trying to plug a hole in the universe, what are you doing ?. "
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My pcm shows cts correct temp when go to the ipc shows 100 degrees constant. Today ipc started showing correct temp. Thanks for the reply. It would be different if pcm showed incorrect temp. Thanks.
Side question for Andy - why is the value lower with power probe? I noticed recently on an IAT sensor unplugged on my PP that the 5v ref was reading like 4.2v and I was questioning it since I had 5v at the TPS. It must have something to do with there being a resister at the other end of the NTC circuit and the small load the tool puts on the circuit but I'm not piecing it together in my head.
Today temp gauge worked all day. Don't know what happened or what caused the gauge to quit working for 1 1/2 days then started working. Strange. Thanks Andy.
