I was asked to look at this Dakota because the Brake warning light and the ABS lights come on.
I get no stored codes with my code reader, and upon test driving it I found that the lights both go off when you shut off the truck, but each time you start up and drive off…those two lights will come on the first time you hit about 30mph and then stay on until you shut off the truck again. Restart and the lights are off until you drive off and hit about 30mph again.
Backing out of the shop, stopping, turning around, down the driveway 50yds and stopping at the road…the lights stay off, even though I just used the brakes three times at least. Get on the road and hit 30mph and they go on.
The two fuses, one in the fuse block by the drivers door and the other (ABS) fuse in the Power distribution box test good.
Both brake lights work at the rear as does the high mount brake light.
Fluid is at the full mark.
I pulled all four wheels and drums on the back and inspected everything and everything looks good and the E brake cables are intact and working as they should. Brakes were replaced (not by me) and have a little wear, but plenty of material left. No leaks of any lines, calipers, or cylinders. Front rotors are not scored from a sticky caliper, they do have a little minor rusting but because it has been idle for a few months.
I have the same year and drive train in my Dakota. Their truck has about the same stopping power as mine, but I did notice that I did not feel the surging in the ABS as I feel in my truck. I tested this by traveling at about 40mph with the passenger wheels in the gravel and drivers wheels on the pavement and applied the brakes hard. In my truck I felt the surging, but not in theirs. Note that my truck has a tall cap and always carries an extra 800 pounds of gear in the back.
Maybe the heavier weight makes my ABS kick in quicker, but I would think weight wouldn’t matter…one wheel is slipping…period.
Any ideas on what I could or didn’t do that might help pinpoint the problem. Before I send them to the dealer.
I may drive it to my parts store tomorrow AM and see if they get any codes.
There has to something wrong in the primary brake system.
If the primary brake warning light comes on, it’ll cause the ABS warning light to automatically come on. Because the ABS is telling you, “Dude, I’m not going to function until you fix what’s wrong with the primary brake system.”
Your code reader is only giving you codes for the Engine Control Module. Most code readers, including the McParts store’s, will only give you those codes. The codes you need include those from the ABS module and you need a code reader or scan tool capable of reading those modules to pull those codes. This time, you’ll need a professional to look at it, someone who has a more sophisticated tech gear than you.
I may be wrong here, but the only things that would turn on the Brake warning light would be the E-brake switch (but then it should be on always with the ignition on) or the fluid level sensor.
You may have two problems. A wheel speed sensor and a problem with the main system.
It’s possible that when the brakes were recently done the parking brakes were not properly adjusted. That could illuminate the brake warning light.
It’s also possible that the reservoir in the master cylinder was not properly refilled, or the cap wasn’t put on properly and the float is hung up. I’d consider the first part a high probability, because if the fluid is low, when you use the brakes the first time it might be pushing enough fluid into the wheels to cause the float to drop below the level that will illuminate the brake warning light.
It’s also possible that when the brakes were recently done a wheel speed sensor was knocked off or not properly plugged back in. That would illuminate the ABS light.
I’m leaning towards a problem with a wheel speed sensor
Put the truck on jackstands
Spin each wheel, while monitoring the sensor at that corner. I don’t know the specifics of this particular system, but I’d be looking at AC voltage
you may have a dirty or damaged tone ring
Here’s the good news, in my opinion. I don’t think any of the wheel speed sensors or the wiring are open circuit or short circuit. If that were the case, the light would stay on, after the engine was idling
I checked both front wheel speed sensors and they are installed properly and plugged in.
Though maybe I should unplug them and check for corrosion, but then I would think that the code would be stored and not reset when the ignition is shut off.
The fluid res is at the full mark but I’ll check the float.
I carefully checked the rear drum brakes and both sides had to be backed off to remove the drums. There is a very little lip on the drum edge, and had they been not adjusted…I could have pulled them easier without backing them off.
With the drums off I applied the e brake and the actuators are working and cables intact and spreading the shoes like they should.
I’ll have to call the owners in the AM and ask if this started as soon as the new brakes were installed.
“I checked both front wheel speed sensors and they are installed properly and plugged in.”
Bud did you check their output with the multimeter?
For what it’s worth, I’ve seen many speed sensors whose resistance checked good, and the light turned off after the engine was idling. So they passed that self check
But . . . when a certain speed was reached, the abs light would come on. And it was due to the fact that one of the sensors was producing a low signal. In a few instances, this was due to a dirty tone ring. And because I’m a good boy, I rechecked the signal after cleaning, and it was now within specs
It couldn’t be open circuit or short circuit, in my opinion
This almost sounds like a situation where you’re driving a vehicle, and one wheel only gets “airborne” because you went over a gigantic pothole, and that corner lost traction for a split second
The abs/traction light will illuminate, but there’s nothing wrong with the vehicle. The abs module saw a discrepancy in wheel speeds
Or when somebody’s teenage son does figure eights and donuts in the parking lot, and causes the traction/stability control system to kick in. The warning lights will illuminate, but there won’t be any fault codes
I’m just throwing ideas out there, and I may be way off base
This may seem off base but if the alternator is producing excessive AC ripple it might cause this kind of issue with the warning lights. I would think though that if that was the case then the lights would go off when you are below 30 MPH. Just to make sure that isn’t the cause of the trouble you could remove the rear connector to the alternator and then start up the car an go for a test drive. The battery warning light should come on of course.
Since you say the issue happens at speed I wonder if the issue is related to the engine vacuum system and the brake booster. Maybe monitoring the vacuum system would show up something.
I got it fixed and had to replace the wheel speed sensor and bearing hub on the passenger side.
Turned out that a stone must have gotten flung through the space between the dust plate and the rotor. Whatever it was it knocked the guts out of the sensor and even bent the exciter ring that is pressed onto the hub. The ring was bent at least an 1/8th inch. When you spun the bearing by hand the ring wobbled like the wheel on Benny Hills bike.
I can’t see why it would get bent by the tech that did the brakes, but I suppose it is possible.
I’ve seen plenty of drums beaten all to heck by someone who did not back off the adjusters like they should. Maybe they had that hub replaced once and the mechanic pried on the exciter ring…who knows.
I got a new hub and sensor this morning and had the truck done by noon.
Thank you all again for the ideas. Your input is well appreciated.
Thanks for the update @Yosemite. Glad you got fixed. It looks like my ideas for the trouble weren’t even in the ballpark. It seems like there should have been some sort of error for the trouble.
