ABS light

[Janss]

The anti-lock brake system light on my dash comes on occasionally and randomly. It doesn't come on every time I drive. It may not come on for hundreds of miles, like all the way from Sedona to Oregon. Then on the way back, it just happens to come on. After I stop and start the engine again it's not on. Today was the first time the light turned off while still driving (after it randomly turned on while driving).

I just had the MH to a Chevy dealer for that and other stuff. They tested the ABS system and said it's working fine and there were no error codes. And of course the light was not on while at the dealer. They had no other advice for me.

I'm not at all knowledgeable about auto mechanics.

So I ask anyone here for ideas. I guess I feel a little more comfortable that the dealer checked the system. But still a little uncomfortable. Could it just be a loose wire in the dash or in the system, or a fuse problem?

[bucky]

This is the reader I referenced
code reader clicky

The plug you will access should be close to the steering column.

[Janss]

Thanks for the additional comments.

j-d, I really do mean I lack knowledge and am not a DIYer in auto mechanics. Well, I can check the oil and add some fluids 🙂 I do appreciate your time and effort to educate me.

I wish I would have asked about this before I picked up my coach from the shop. Oh well, I'm sure I'll have another chance sometime to talk with a mechanic who is willing to delve deeper than this dealer. As noted, now I will know what to discuss and ask for.

bucky...Interesting idea about the code reader. I had to look all that up. I'm going to look for the plug outlet in the MH.

[j-d]

Trying to pull everybody's responses together...

Because you live in beautiful dry Sedona... I'm thinking you might be less likely to have dry rust around the front sensors. By "dry" I mean NOT in a closed, oily lubricated area like the rear axle.

Based on that, I'd still like to see if you an access the sensor for the Rear Wheels. The RockAuto site shows NO sensors for W-series, but does show them for P-series (the bread trucks, UPS/FedEx trucks, etc. Here's a picture of one.

The Sensor part of it is below that reddish O-Ring that seals it into the lubricated environment which could be a rear axle (like Ford) or a transmission (that seems to be the case with Chevy/Workhorse). The connector is probably two-wire (if similar to Ford) and goes into the oval shaped hole. The little triangular "shark fin" sticking up latches the connector.

The RockAuto lookup (again for P-series, they don't show them for W) shows two of these, transmission mounted, identical, one for Input Rotation the other for Output Rotation. Output would be the same as the front of the Driveshaft. Ford uses the Differential for its sensor position, equivalent to Output on Chevy, probably same on Workhorse.

I'm hoping an RV Tech jumps in on this. I can see how the Ford style, axle mounted, can pick up "dross" from wear on the differential gears. Transmission pans often have a magnet in them to trap that dross, but I suppose a transmission-mounted sensor (sometimes called VSS for Vehicle Speed Sensor) could still trap dross even with a pan magnet.

In the absence of more info, I'm for finding the VSS (one or two on transmission, maybe one on axle). Clean the area around it/them, then pull, clean, put grease on O-Ring, reinstall. Cost is $zero. See if anything changes.

[bucky]

There are code readers that include ABS codes as well as emission codes. HF has a reasonably priced one for the occasional user. Keep it in the MH until the light comes back on and plug it in without turning the MH off. Knowing the code(s) can save serious money.

[theoldwizard1]

I had problems with my ABS on my E150. Replaced both front wheel speed sensors (about $40) and the problems went away.

[time2roll]

My ABS light was a bit intermittent for a few years.
Have not seen it since the alternator gave up and exchanged for new.

[drsteve]

Had an intermittent problem with ABS on my truck. Turned out to be moisture gets behind the sensors, and corrosion slowly forces them out of the hole they're mounted in. There was a TSB, IIRC.

[hawkeye-08]

If I recall, GM had some issues with sensors on front of pickups and SUVs (likely your motorhome if GM chassis). I want to say it was a bad ground or something similar on front sensor wiring? Perhaps look up TSB (technical service bulletins) for similar chassis looking for ABS problems?

http://www.bbbind.com/free_tsb.html

[Janss]

Sure appreciate all the different posts and thoughts. Since I am not a DIYer in the field of auto mechanics, this thread has given me what I need to know next time I'm with an able and willing mechanic, such as asking to follow the wiring and checking the sensors.

wowens79...I did read or was told that even if the ABS (anti-lock) isn't working, the regular brakes still work. I avoid driving in bad weather, so I think I should be okay with it.

j-d...I do have the Chevy Workhorse 8.1L. Not sure which "W" chassis it is because I thought I read in manual one number and then when a shop replaced my fuel pump they told me it was a different number. ABS light does come on when I start the engine, then off seconds later. My problem happens after I've been driving awhile it comes on. I appreciate your detailed response. Think I understand your bottom line that it could be either a dirty sensor or a failing sensor.

path1...Why fix it if it ain't broken? Maybe a hose clamp works better than a new connection 🙂

TurnThePage...Definitely not wet and cold. Has always been sunny and dry when this has happened.

Thanks again everybody!

[MEXICOWANDERER]

You "could go" to the car dealership and fib and tell the service manager "I have a friend in Guatemala and he has..."

And ask to read a copy of a factory TECHNICAL SERVICE BULLETIN dealing with a false flashing of the ABS light

"Gee I'll even buy the parts here, if I know what to send him"

My honest nature ends when dealing with new car shops. A sour lesson learned after wrenching for one some forty years ago or so.

[TurnThePage]

Maybe not related at all, my old '97 F150 would experience that intermittent ABS light, but almost exclusively when it was wet and cold outside. Never any trouble found by various mechanics looking at it.

[path1]

Maybe you'll get lucky like I did and Yes, pretty hard to fix something when its working, then later when not at a shop it messes up. On mine (that is different make and model) I found everything I could on-line, and also found out there are many reasons why an ABS light goes off. Then I started with the simplest first. The simplest for me was following the wires and at every connection make sure the connection was tight. I found a loose connection right above my diff cover. A loose connection as in when I pressed the connection together real hard, the ABS light went off. Then I put a big hose clamp around it, waiting until I ordered a new connection and had time to put it in. Well that was several years ago, no more problems. Thanks for refreshing my memory, maybe I'll get around to ordering another connection?

[j-d]

Which Chassis do you have? I take it, a Workhorse since you had it looked at by a Chevy dealer... But more important to know which Year/Make/Model of Chassis vs. the Coach to deal with an issue like this. That said, I guessed W22 with 8.1V8. Then tried to at least look up some parts. RockAuto.com shows Workhorse, and their selection for braking was very limited and nothing for electronics. So no joy. A 2002 Ford F53 chassis has a sensor on each front wheel (close to the hub) and one sensor at the top center of the rear axle (above the Ring Gear). Working on our Fords, I've seen dry "dross" clinging to the Front Sensors, and greasy "dross" on the Rear Sensor. This is because the Sensors are mildly magnetic, and the fronts are out in air, while the rear gets axle lube slung onto it.
That "dross" is from wear on the rear and wear along possibly with rust on the front. Normal if it's not excessive, but too much will bother the ABS "brain" and put the Light on. If it was mine, or we were together and I could help you, I'd try to pull the Sensors and be sure they don't have Metallic Stuff clinging to them. Again on Ford, the Sensors are held in place with little 10mm fasteners. The Rear has an O-Ring Seal, and since it's into the Axle Lube, I clean the mounting area with spray brake cleaner before removing it so dirt doesn't fall into the axle.
I don't think the Sensors can be tested with ordinary tools like a Digital Volt Ohm Meter (DVOM). On Ford, I'd risk $10 on the Rear one, but the Fronts are closer to $100 each.
Again on Ford, the ABS does a "self test" every time you start the engine, so I an understand how it might set the light while driving then not light it next time you start up. On one of our Fords, a failed Rear Sensor turned the Light on and off while driving. It also took the Cruise, Speedometer, and Overdrive with it.

[wowens79]

I've got the same issue with my Chevy truck. I'm guessing it is a sensor going bad. My understanding is when the light is on, the brakes work, but the a it-lock is not working.