ABS problems on the van

I am having ABS issues on my van. The ABS brake system kicks in at very low speeds on dry pavement. There is a service bulletin about rust on the mount point of the sensor causing it to pull away from the hub so the signal is erratic. That would be a simple fix as the sensor is $200. I can not find a cheap overseas replacement part even on Ebay. My scan tools shows a couple of generic ABS chassis codes:

C0281 (chassis code - ABS) Brake Switch Circuit
C0223 (chassis code - ABS) Rt Front Speed Signal Erratic

I suspected the right front wheel so this confirms it. The test procedures specify resistance and voltage readings for the sensor. Getting the voltage reading is going to be a trick as I can not spin the front wheel as I have all wheel drive. I will have to disable the ABS then rig up a cable to attach to the harness so I can roll the van down the driveway to measure the AC pulse train. The voltage is very low (approx 100 millivolts) so noise is going to be a problem even using the oscilloscope. The service bulletin indicates the signal should be at least 350 mV but this document says greater than 100 mV. So much for consistent documentation.

The procedure also measures the cable from the sensor to the electronic brake control module (ECBM). It states that faulty wire connections is a leading cause. The darn EBCM is attached to the frame under the van. That is the dirtiest place you could put the thing.

I am a little confused by the C0281 code for the brake switch circuit. The description indicates that this code may set if the there is an ABS fault of at least 500 milliseconds. That would have set by the C0223 code but then in the next line it says the code only sets if there is an open or short in the brake switch circuit wiring. For now I will assume it is setting because of the sensor signal. Fix that and then see if C0281 comes back.

The last item in the correction chart is to replace the ECBM. Unfortunately you have to have a scan tool that communicates to the device. Consumer scan tools only read diagnostic codes. You need on of the expensive units to talk to the devices. You have to set the tire diameter for the vehicle in the ECBM. Crap! If that is bad it is back to the dealer to replace that darn thing. I bet they get a lot of $$$ for that module.

Over the weekend I hope to get a chance to investigate the sensor/wiring.