C0040 code

Abs code C0040 is RF sensor circuit. Common GM issue and lots of replies are for actual wire harness and not the sensor in wheel. The short harness from wheel bearing to plug at fender liner is 18”. How about the next harness from liner to control module? How do you track down what harness may be the issue?

If you have a short, ring out the cable. Check continuity of each wire in both cables. When you get an open, you found the offending cable.

if i clear code and i have a broken wire or bad sensor, will the code return when i restart the car? or do i have to move so computer can see rotation in wheel sensor?
so a broke wire means the computer sees a problem before i move?
and a bad sensor will not be seen until car is moving?

You may have a wheel bearing (or hub) going bad. The slightest wobble will damage the sensor.

Good ideas above, especially about measuring the resistance of the wheel speed sensor at the various connectors between it and the computer. If you have a scan tool that has the required wheel speed sensor test function you can drive the car around and measure what each sensor is saying the wheel speed is for each wheel.

If you don’t have that scan tool, measuring the resistance is where I’d start. Usually in the range of 2,000 ohms I think. If you measure 2,000 ohms right at the sensor (with the sensor disconnected), then upon re-connecting the sensor you measure, 2 ohms or one million ohms at the next connector in the chain, there’s obviously a problem in the wiring between that point and the sensor. Disconnect the battery first before doing resistance tests.

There’s different configurations for those sensors, some are just a simple coil of wire, the passive type. Others have an electronics package inside the sensor, the active type. Not sure how it works on a Nox, which is what I presume you are testing. If you have a lab o’scope you could trace the signal from the sensor to the computer as you hand-spin the tire. That’s how I’d do it. Without a scope you could approximate this test just using a DVM in AC voltage mode. You should see something in the neighborhood of one volt AC when the wheel is spinning; if you have the simple coil of wire type, the AC voltage will be higher the faster it spins. Comparing known to be working sensors with the one is question is helpful too.

Maybe this is reason?


Was the wire broken inside the outer sleeve, and you had to remove the sleeve to figure it out? Or was it like that when you first discovered what the problem was? If the latter, I wonder how that happened?

I was in the process of removing the wheel bearing and noticed the white sleeve was loose and slid it back and saw the break. this is wire from bearing. i might run over to the junkyard and grab another one with a longer lead that is not broken so i can make a bettter connection. use crimp connectors

I would think that’s a good place to start. :wink:


went to boneyard and got a new plug. funny that the 2 noxs i looked at both had a wheel sensor that can be separated from the bearing housing. and mine is not like that. the sensor lead is routed to the inside of the bearing and looks non replaceable.

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