Testing abs/speed sensor

[cmichaelo]

I'm getting "Rear wheel speed sensor" 005DC3 error on my E92 M3. I bought a new sensor and decided to test it before installing it. One website, for a non-M3 though, indicates that the correct resistance between the two terminals should be around 700 ohms. Well, I'm seeing an open. I also tried testing for diode, but see again an open. Also tested for capacitor, again see an open.

Does the sensor need voltage before it can be tested properly?

Any advice appreciated.

[Rainer M]

Originally Posted by cmichaelo

I'm getting "Rear wheel speed sensor" 005DC3 error on my E92 M3. I bought a new sensor and decided to test it before installing it. One website, for a non-M3 though, indicates that the correct resistance between the two terminals should be around 700 ohms. Well, I'm seeing an open. I also tried testing for diode, but see again an open. Also tested for capacitor, again see an open.

Does the sensor need voltage before it can be tested properly?

Any advice appreciated.

I can't help with precise info but perhaps comparing it to another sensor on the car helps.
There should be a sensor in the front.
Perhaps on every wheel?

Rainer

[cmichaelo]

Originally Posted by Rainer M

I can't help with precise info but perhaps comparing it to another sensor on the car helps.
There should be a sensor in the front.
Perhaps on every wheel?

Rainer

I was told by ECS tuning to test them from the ABS module while turning the wheel and I should see the voltage across the pins change as the wheel turns.

It's a pain to take off the wheel well cover just to obtain a good sensor. So I only compared against the supposedly broken sensor and which shows the exact same characteristics as the new one.

I did notice the old sensor is quite worn down on the side of the tip of it that faces the sensor ring on the wheel hub. I'm suspecting the sensor either is too close to the sensor because the sensor ring has been pushed towards the sensor due to rust building up behind the sensor ring on the wheel hub, or for some other reason the sensor ring has moved, and is now "carving" its way into the sensor tip itself causing it to fail.

I'm gonna try to move the new sensor away from the sensor ring (towards the center of the car) by shaving off a little bit of the plastic spacer at the top of the sensor.

[eatsleepboost]

There should not be a gap between the abs sensor and the tone ring. It's normal to have marks on the end of the sensor as it rides almost against the ring. If that tone ring is bent or cracked it will affect the readings and throw an abs error code. Also, yes spinning the tone wheel while having and a/c voltmeter on the connector contacts is how to test those sensors.

It's a half hour job. Just install the sensor and drive it. You can monitor and record/graph your wheel speed sensor reading on a decent scan tool. If you just install and drive it the light will go right out once it sees near identical wheel speeds are each corner.

[cmichaelo]

Originally Posted by eatsleepboost

There should not be a gap between the abs sensor and the tone ring. It's normal to have marks on the end of the sensor as it rides almost against the ring. If that tone ring is bent or cracked it will affect the readings and throw an abs error code. Also, yes spinning the tone wheel while having and a/c voltmeter on the connector contacts is how to test those sensors.

It's a half hour job. Just install the sensor and drive it. You can monitor and record/graph your wheel speed sensor reading on a decent scan tool. If you just install and drive it the light will go right out once it sees near identical wheel speeds are each corner.

Here's the side by side of the old and new abs sensors:



It can be clearly seen the old sensor is being eaten up by the sensor ring. The left side showed same carvings into the sensor head. I'm suspecting rust behind the sensor ring or dirt build up on top of the ring causing this. Others have reported similar issues on non-M E9x cars. I carefully brushed the sensor ring with a small pain brush and inspected the sensor ring as best I could. They looked fine on both sides. No breaks. All smooth and pretty. So I moved both sensor heads out by, say, a 1/4 mm or so (so small I can only guess).

So far so good.