I need a bit of help figuring out a wheel speed sensor issue.

The vehicle
2004 (late version) X-Type 3.0L
ABS light is on.
check engine light is on.

The code
C1155 - Left front wheel speed sensor circuit failure

My actions so far.
1. checked for continuity (ohmed out) the wires from the wiring harness connector to the abs module.
2. ohmed out the wires the short wiring harness that connects to the wheel speed sensor.
3. I reconnected the wires and ohmed out from end to end.
4. I replaced the wheel sensor with a brand new one.

And yet my abs light persists as well as the C1155 DTC issue.

What else can it be? And ideas would be greatly appreciated.

Thanks

 

If sensor and wiring is all good then your problem could be in a faulty wheel bearing.

 

What I would suggest you do is remove the wheel sensor
attach your ohm meter to the connections and then place a fridge magnet on the sensor and see if you get a change on your ohm meter this should tell you if its the sensor is still detecting the magnet in the wheel bearing.


EDIT..
Sorry bad information this may not work with our sensors. you will need an oscilloscope not a meter

 

I had the same issue and after checking everything including wheel bearings I send off my ABS computer module and had it repaired. It fixed the problem. Cost $125 and was worth the cost to not see that light any more. I think they get a loose solder joint inside the unit.

 

I already tried the refrigerator magnet and didnt notice any change in the resistance of the wheel sensor using an ohm meter. I dont have a scope. I wish the typical DTC scanner had that feature.

I will probably pull off the wheel hub to make sure there is not issue in there.

How exactly does the wheel sensor work? Does it create an electromagnetic field that senses the "toothed" gear inside the hub? Or are the "teeth" on the gear magnetic?

This particular wheel area (the inside of the wheel, the strut, control arms, etc...) was loaded with old grease and oil. Is it possible the toothed gear is dirty causing my issue?

I know that one other possible test is to swap the wires at the ABS module connection for the left and right front wheel sensors. I am not sure how easy it is to remove the wires from that connector. I just dont want to mangle that connector..........it would make the problem much worse.

 

There are magnets on one side inside the wheel bearing, not visible to eyes but can be seen with magnetic test card.

One like this:

 

simply put the sensor is a coil of wire and there is a magnet in the bearing.
when the magnet passes the sensor it induces a pulse and the pulses per second is measured as speed by the computer.

 

I have been driving my x-type a bit more and noticed that the ABS sensor appears to be a somewhat intermittent problem.

about 50 percent of the time the code is not there until I drive about 1/4 mile. I even felt the antilock brakes actually work one time.

Given that I have a new wheel speed sensor what is the likely culprit here?

 

GMC, if the signal is dropping in and out, it can be a number of things. It is sounding like you have ruled out the wiring, but this leaves you with either the computer being bad or the wheel bearing being bad. The only way that I can see you being able to distinguish between the two is to run a second set of wires from the sensor to inside the cabin of the car. These wires would run in parallel to the sensor. Then using an o'scope (best, but a multimeter should work with a frequency setting would work too), you can drive the car down the road and see the frequency and pulse height of the signal. If you then compare it to say the other front wheel, you can then isolate whether it is a sensor/wheel bearing issue or if it is the computer that is not playing nice.

I guess the other thing that you could do is to get into the ABS module plug and switch the wires between the front wheels (this would only be a temporary thing as you can affect the safety of the vehicle with how the ABS treats the car). Then if the problem stays with the same wheel, you have confirmed it is a computer issue. If the problem moves over to the other wheel, then you have a bearing issue. But, this is a lot of work to access the plug and to then carefully remove the wiring to switch it around to only have to do it a second time to restore the car to normal. if you want to do the wire swap, let me know and I can tell you what wires you will need to mess with.

 

thanks for the Info Thermo. I am dreading this little diagnostic nightmare.

if it is the wheel bearings is this just a standard outer wheel bearing, inner wheel bearing or part of the front axle (ie. the halfshaft)

It would be nice to have the ABS light go away and I assume this would make my cruise control work.

 

GMC, the wheel bearing is a single unit that can be replaced independent of the CV half shaft. The big thing to remember with the front wheel bearings is that they have an inner and outer side. So, you need to make sure you orientate the bearing properly. If you don't, then the magnets are not in the proper location and the sensor will not work at all (just ask some of the members here about that).

 

I have an update on the wheel speed sensor issue.

Today I was driving the car and the "Brake" light turned on.

I checked the codes and now I have
c1145
c1155
c1165
c1175
these are open circuit codes for each of the 4 wheel sensors.

It sounds like the ABS controller might be at fault but I dont want to jump to any conclusions.

What else might cause all 4 wheel sensors to come on at the same time and also trigger the "brake" dashboard light?

 

It looks like the abs module has gone out. I had 2 go out on my cars and replaced them and all was good. If you need one I have 3 units. Pm me and we can talk price