: Temp sensor circuit



98Geldog
07-16-13, 04:13 PM
Had this problem for a while now and it's causing a miss. Coolant temp sensor circuit is the only code. I've changed it twice. So obviously it's in the actual circuit not the sensor itself. Problem is I don't know where the wires go to check the circuit and can't find any info. Hopefully someone can help me here thanks

investor74
07-17-13, 07:49 PM
You are getting a P0115? Anything else? There are other related codes.

One side of the ECT sensor goes to ground and the other to the ECM. Can you get to the cable coming out of the sensor? Careful you don't mess up the connector by sticking too big a probe in there.

The ECM applies a 5 volts signal. When the engine coolant is cold, the sensor resistance is high and the 5 volts from the ECM is only pulled down a small amount, so the ECM senses nearly the full 5 volts. When the coolant temp is warm, the resistance of the sensor is low, which pulls down the ECM signal a greater amount.

So you need to check for the 5 volts from the ECM and that the other side has no resistance to ground (ohmmeter check). More complex test gear may be required to see if the voltage is where is should be at any given temperature. However, if you are getting the 5 volts there and the other side well gounded, it would seem that if you still have the problem, it is the sensor, not the wiring.

98Geldog
07-18-13, 03:56 PM
Thanks for replying. Yes 0115 is the only code. I will check for continuity on ground and the 5v from the ECM that's the info i needed to know. By the way what sensor brand do u recommend? The two I replaced before we're from orileys auto parts I think BWD brand. If I don't get a ground could I just ground it to the body or does the ECM need to read that? Thanks

investor74
07-18-13, 08:35 PM
The ECM has its own ground so it doesn't need one from the sensor cable. I saw in the manual that you can try jumpering the ground side of the sensor to a known ground to see if works as a test, but not sure if it is recommended to run the sensor permanently that way. Not sure about recommended sensor brands.