Originally Posted by 98z28darkhell
its not the guage beacuse the snap on modis reads -38 all the time unless u jump the wire and the it goes up to 238. so its not a cluster related proble beacuse the guage actually works. the ECU is not reading the ect until u jump the wires. The Snapon modis scan tool never reads a temp. until u jump the wires and then it reads 238
That was confusing to me.
With the wires connected to your ECT sensor, you're saying that scanning the PCM never reads a real temperature?
Assuming the wires plugged to the ECT, your scanner says -38*F.
Assuming the wires unplugged from the ECT, your scanner says -38*FF.
Is this correct?
How exactly are you jumping the wires? is it at the plug where they contact the ECT sensor? Is this a 2-wire sensor plug?
-38*F reading shows an open circuit.
That can mean that the plug is defective and not contacting the sensor.
If your PCM scanner shows a real temp, but gauge doesn't work, then you either have a faulty gauge circuit, or the gauge gets its signal from a second ECT sensor.
I have seen cars with:
One one-wire sensor
One two-wire sensor
Two two-wire sensors
One three-wire sensor
One sensor for the PCM and one sensor for the gauge
and a few other variations of one-wire sensors in cases where the ECM/PCM takes ground through the engine (older cars).
By the way, the power-on gauge sweep function is a separate circuit from the ECT signal, and is common to all (or most) of your gauges.