I've got a persistent issue with my ABS. During the winter my ABS light would sporadically come on and often would trigger the abs at lower speeds. I took it to a shop to have it examined and they pulled the following codes:

C0021 RF speed sensor circuit open / short
C0022 RF speed sensor signal missing
C0023 RF speed signal erratic

I didn't really have the means to fix it at the time so I just pulled the fuse and went without abs until recently when I decided to fix it. I pulled everything off and took a look at the sensors and as the shop described a portion of the wires had corroded. Went ahead yesterday and installed the new ABS sensor and everything went smoothly.

I took it for a drive after getting everything back together and within about 10 feet the light popped on. I stopped by Partsource to have them read the codes but nothing came up (I explicitly asked for a ABS read as I have a generic OBD II reader). I thought maybe the connector got some dust in it during the install so I cleaned it out, the issue still persists. When I unplug the sensor the vehicle starts up and the abs stays lit (As it should), when I plug the sensor in it stays off until I start moving.

My only conclusions at this point is that maybe I installed it wrong, everything appeared to fit just as it came off, also maybe the scanner the dude at Partsource used was wrong (I'll probably take it to shop tomorrow to have them read it). The sensor is intregrated into the dust shield so I'm doubtful it's the hub. The part I installed is here: .

Any thoughts or leads into the issue would be greatly appreciated. The vehicle is a 1997 Chevy Blazer 4x4.

 

Best I can tell you is what you've already stated, make sure you have someone with an ABS scanner to see what the code(s) is/are. Could be that you got a bad sensor.

 

Are your front hub bearings OK? When one of mine went bad it used to cause the ABS light to come on occasionally, presumably because the play in the bearing was upsetting the gap between the toothed pulse ring (inside the hub) and the sensor itself. It also used to trigger the ABS at low speeds when coming to a stop, it wasn't a nice feeling as I recall?

Also, when I replaced my hubs (which came with new sensors fitted) before I threw the old ones away I removed the sensors from them to keep as spares in case I ever needed them. I noticed that they were fitted with shims underneath them which presumably sets the required air-gap between the sensor & the toothed ring, guess it must be pretty critical?

 

I've repaired them in the manner that you've stated with 50-50 success..there are ways to pre-check you're work before putting it all back together(with a multimeter) but if you have an intermittent issue...well, it may not show at that time. I would re-check the code and if you wish to fix you may have to install a new bearing and ABS wire. If you had a scan tool with the ability to look at speed..I think you would see that right side 'drop out'..It would register mile per hour but miss 1 or 2 mph's. I (after seeing that) will usually hook up a new bearing and spin it by hand looking @ the mph's and see the difference-hopefully not 'dropping out'...this has been a good way for me. In short, you may have done everything correct..some I just can't get in this manner for some unknown reason..Jerry PS good luck!

 

At the ABS module on the fender you can pull the plug for the two wheel sensors and take readings from there. Easier than doing it in the wheel well. Jack up the vehicle and plug in a multimeter then spin the wheel and see what ACmv its reading. Rotate the wheel clockwise approximately one revolution per second. The minimum reading should be at least 350 ACmV's.

Good luck I am going through the same thing. I will be testing mine again this weekend. I am thinking it is something with the air gap. Problem is with our systems that air gap is not adjustable because of our wheel sensors being mounted in the dust shield. I have two new sensors and two new hubs and the ABS is kicking in when it shouldn't be.