ABS Events & Discoveries

[C&H from NorCal]

A few months ago I had Les Schwab Tire rotate my 2006 Alpine's tires. Despite my objections (obviously not forcefully enough)they bled off the suspension air then used the hydraulic levelers to raise the rear axle off the ground, lifting both rear wheels. As soon as I pulled out I noticed the yellow ABS caution light stayed on. I called Schwab back. They initially disclaimed any responsibility. I called WRV several times and got the "WRV shuffle" ie. "Don't know", "try this", "try that", "drive it a few miles", etc, etc, etc..

Several months and thousands of miles later the light is still on. Schwab, an RV dealer and I all looked for disconnected wires and found nothing. I took it to a Kenworth dealer but they couldn't connect to the computer data port. I contacted Wabco/Meritor and downloaded their manual and disgnostic procedures from their website (a GOOD doccument to have)...

I found the ABS data port and "blink code diagnostic switch" were on the passanger side firewall, behind the velcro'ed panel, ahead of the passanger's feet, not in the battery compartment where the ABS ECU is located (and where Kenworth tried to connect). I followed the W/M manual flipping the switch labeled "ABS diagnostic" without any reaction. Finally, out of frustration I flipped the switch labeled "engine diagnostics" and guess what? The ABS blink code started.. WRV has them mislabeled. The switch on the right is for engine diagnostics the switch on the left is ABS !

The blink codes say I have an "air gap" in the right front ABS and "continuous voltage to the ECU with the switch off". I checked the wires between the ECU and right front wheel for shorts, grounds, etc and found nothing. I have re-set the ECU codes and will drive down to the NoCal Lodi Rally this weekend and see if the light re-sets and goes off. If not I'll be back on the phone to W/M... Harold

[C&H from NorCal]

A few months ago I had Les Schwab Tire rotate my 2006 Alpine's tires. Despite my objections (obviously not forcefully enough)they bled off the suspension air then used the hydraulic levelers to raise the rear axle off the ground, lifting both rear wheels. As soon as I pulled out I noticed the yellow ABS caution light stayed on. I called Schwab back. They initially disclaimed any responsibility. I called WRV several times and got the "WRV shuffle" ie. "Don't know", "try this", "try that", "drive it a few miles", etc, etc, etc..

Several months and thousands of miles later the light is still on. Schwab, an RV dealer and I all looked for disconnected wires and found nothing. I took it to a Kenworth dealer but they couldn't connect to the computer data port. I contacted Wabco/Meritor and downloaded their manual and disgnostic procedures from their website (a GOOD doccument to have)...

I found the ABS data port and "blink code diagnostic switch" were on the passanger side firewall, behind the velcro'ed panel, ahead of the passanger's feet, not in the battery compartment where the ABS ECU is located (and where Kenworth tried to connect). I followed the W/M manual flipping the switch labeled "ABS diagnostic" without any reaction. Finally, out of frustration I flipped the switch labeled "engine diagnostics" and guess what? The ABS blink code started.. WRV has them mislabeled. The switch on the right is for engine diagnostics the switch on the left is ABS !

The blink codes say I have an "air gap" in the right front ABS and "continuous voltage to the ECU with the switch off". I checked the wires between the ECU and right front wheel for shorts, grounds, etc and found nothing. I have re-set the ECU codes and will drive down to the NoCal Lodi Rally this weekend and see if the light re-sets and goes off. If not I'll be back on the phone to W/M... Harold

[jerry davis]

Harold you obviously have loose nuts besides being mislabeled.
See you in Lodi.

[Dave Fernandez]

Hello & Welcome C&H:

Next time you are under the coach look for the ABS sensors in the backing plates and push on them to make sure that they are seated in backing plate. The sensors are only pushed in and do not have a screw or locking mechanism to hold them in. There is one sensor at each wheel. They sometimes the sensor moves out away from the rotor increasing the air gap.

[William Schnieber]

I thought it was just mine-I had the same prob, they ended up finding the problem behind the dash(so they say-they probably just disconnected the light)they said it was a loose wire at the connector to dash. My diag. said it was at the drivers front wheel so I tried adjusting the sensor but still had the problem. So try looking at all your wiring connections also. Good Luck.

[C&H from NorCal]

Dave you are EXACTLY RIGHT. After driving to the Lodi ACA NorCAL rally and back home (350 miles) the ABS caution light was still on. I took the coach back to Les Schwab and they pulled the right front wheel and the only thing we could see was the gap between the ABS sensor and the geared spline was about 1/4-3/8" and there was some debris on the sensor. He cleaned off the debris but the light stayed on. I called Bill Hiles (very knowledgeable guy) @ Meritor Wabco and was told the large gap was the problem, When we inspected the wheel we didn't see any means of adjusting the sensor, no threads or bolts....Turns out the sensor is just pressed into the backing plate, a couple of soft taps on the back of the sensor drove it against the geared spline and it self re-adjusted after a few revolutions of the wheel and the light WENT OUT !!!! Interesting thing is that the Wabco Meritor manual never mentioned checking the "air gap" or adjusting the sensor, it suggested checking wheel bearings, lug bolts , etc....Harold ... P.S. Jerry, my nuts are NOW TIGHT, my bed COOLER and my ABS light out...Hi to Judy & Jake !!!!!

[SteveS]

Harold/Dave - Do the rear wheels have these sensors also? Every time I have had the ABS light come on (three times) I have just removed the front sensors and cleaned them. Since the problem eventually returns I wondered if the rear wheels might be causing the problem. However, now, since the light is on again, I will check the gap but am still curious about the rear wheels. Thanks.

[Dave Fernandez]

Hello Steve:

Yes there is one in the backing plate of each wheel.

[DrDaveCA]

Harold, I had the same problem when i first picked up my coach. I had Les Schwab install the SmartTire system and when I picked it up I had the ABS light on. LS said they did nothing, so I took it back across the street to Guaranty and after contact WRV they figured out the air gap was too big. Seems the sensor is touchy so anytime you do something with the wheel, I would suspect the air gap. BTW, the blink code will tell you which wheel is alarming.

[SteveS]

Hi Dave:

OK, the next question...can you give more detail to the sensor's location on the rear wheels? Can you get to them without removing the wheels? Thanks.

[Dave Fernandez]

Hello Steve:

If you are looking at the back of the wheel from underneath the coach can be seen on the forward part of the packing plate on the front side of the axle. You will see the Rotor because it is shinny and the sensor will be closer to the center of the rotor. It can be reached without removing the wheels. You will see a single wire going to the sensor and it has a black cover on it. I hope this explanation helps.

[C&H from NorCal]

EVERYONE should go to the Meritor/Wabco website and download their Maintenance Manual # 39 for "D" version cab mounted ECU. This manual gives you all the blink diagnostic codes, ECU pin assignments, etc... Check you motorhome's ECU to confirm which version you have....my 2006 26MDDS has the D version cab mounted ECU loacted in the battery compartment.

[Jim A]

Thanks for the suggestion. Downloading manuals when we find them is always good.

[EngineerMike]

Here is the Meritor-Wabco ABS Troubleshooting Manual link. Nice 2 halve.