This solution is for every car owner with an ABS problem (e.g. Brake System Warning Light).
Does the...
1)ABS warning light comes on occasionally while driving, warning light turns off next time you start the car, eventually the light comes back on if you drive long enough
2)ABS light comes on seconds or minutes after starting or even moving your car
3)ABS sensors have been replaced, ABS controller has been replaced, and ... the problem returns, sometimes soon, sometimes later
4)ABS warning light refuses to act up in front of your mechanic
5)ABS mechanic has no idea what is wrong
6)ABS brake have no leaks to be found, the brake fluid levels are normal and the brake pads pass inspection but the light comes on
My solution will not solve all ABS system warning light problems, but it may solve very many and save many dollars.
This solution just isn't Standard Operating Procedure in our day to day service repair shops as it is time consuming fault elimination. Why is it overlooked, who knows? It should also, in my experienced opinion, be the absolute first thing checked, by the book, before any sensor, control module, brake fluid, brake bleeding, whatever your mechanic suggest... the list goes on for some car owners. The point is, if this isn't checked first, all bets are off for the DIY or even the certified mechanic.
To get my point across to every car owner and MECHANIC will require GREAT effort on my part otherwise this information will be ignored. Now, back to my point, unless this check is made before any car "computer" throws an error code is taken into account, then that error code can be misleading. No ABS red warning light on the dash of all cars or trucks everywhere can truly be CERTIFIED in testing if this process isn't first completed. The odd exception might be the ABS control unit was on fire, you drove the brakes down to metal or some other freak accident. Here's where I say, "for just $9.95, you, can buy this instruction book". Nope this is FREE and will save many people from having nightmares considering the millions of car owners.
Have you ever heard, "A chain is only as strong as its weakest link"? Well, in the real world, ABS errors are almost always misdiagnosed in first repair attempts. The very first thing that should be performed is a visual inspection inside the engine compartment and brake area. Unless there is an obvious loose wiring harness plug, a lost kitten, distorted/bent brake lines, worn out rotors or brake pads, or something else screaming for your attention; then close the hood and step away from the vehicle and put down that silly diagnostic computer. So, now that the hood is closed, we are going to jack up the car and take off a wheel. Once a wheel is off, we need to disconnect the brake caliper and hang it to the side out of the way. Yes, this is usually a painful, very greasy and dirty process; front wheel and four wheel systems are even more fun. Start with the front wheels and work your way around. Now, and only now is it possible to check each Wheel Bearing Torque value. However, just checking the torque with a push and pull of the rotor disk isn't always sufficient. The hub axle bearings and bearing seats need to be inspected, bearings repacked and then precisely torqued. And when I say precisely, in some rare cases that can mean putting all the parts back together, driving the vehicle, tearing the wheel back down and checking the torque settings again. In some cases; hub, axle and wheel bearing assembly just can't maintain this torque value and still rotate properly because just one of the 3 parts may have some flaw, and this leads to rotor movement. It is also very easy for an experienced mechanic to get it wrong. So, it is good to do it right the first time but that also does not mean it always can be done correctly the first time. As good as any mechanic or auto production line worker may be during assembly of these components, all of these bearing components will never "seat" the exact same or show identical performance. They just try to do their best with what they have.
Basically, the ABS electronics are not the weakest link in most cases. If you have proven beyond doubt that the axle bearings are as close to 100% of factory torque settings and the bearings are healthy and lubed, then the weakest link has been removed. Only then should an ABS error code be used to diagnose a possible electronic component failure. All that this axle bearing nonsense means to those still wondering is that the ABS sensor ring will no longer be deflecting off axis as it spins or sits inside the rotor hub. If the hub/ABS sensor ring tilt off axis just a fraction of an inch on some vehicles, the gap between the sensor and ring is affected, and this will trip the ABS warning light. These ABS systems were designed to operate within a specific set of tolerances and unfortunately the bearings in your axles will not always cooperate. A pot hole here, a curb there, too much hard cornering and braking; sometimes that is all it takes to just slightly loosen an axle bearing and have virtually no noticeable effect.
99% probability it is a bad ABS module. Extremely common on these Volvo's. Speed sensor would probably show up on your generic scan gauge, ABS module would not likely show anything. You can get your module rebuilt by sending it in to a number of places. Do a google search for Volvo ABS Rebuild. Victor Rocha is a reputable source for this.
ABS problem is mostly on the sensor, check all the sensors for damage, if its all ok check your abs control module check the wiring and the terminals. spray some wd-40 on it then let it dry for a couple of minutes. the return ,if same problem occurs maybe your abs module is not working well.
Wheel sensors are most common to go bad. they are easy to check. Just unplug jack the car up and have someone spin the wheel, use a oms meter to check miliamps. You see these wheel sensors are like Minnie generators, they send a signal to the module which tells that the wheel is turning. Make sure the tone rings are clean, a leaky wheel seal will cause a dirty sensor. Good luck. If you check these and they are good then go to the module.
I have fixed many others on domestic vehicles that were absolutely plugged up with grease/ oil and lets nit forget that they are magnified....meaning the sensors collect tiny bits of metal particles from grinding pads into nothing but metal to metal, hence the sensor " groves" become plugged up.
I don't prefer the WD40 concept but love using starting fluid which is an alcohol based cleaner that evaporates quickly. Also use air pressure to then blow anything sticking to the sensor off till it's as clean as new.
It is true that bad wheel bearings can cause these pesky problems, but You'll hear the Howling of the bearing or by shaking it briskly if it's loose.
Just remember to start w/ the simplest approach first.
Make sure the scanner you are using is capable of scanning ABS codes on your particular vehicle. I can't tell you how many times I had to rescan a vehicle using my scanner and found an ABS code.
Turn the steering wheel on the F150 all the way to the right. Look at the brake system on the front driver's side of the vehicle. With the wheels turned all the way to the right, you should be able to easily see the ABS sensor mounted to the wheel bearing assembly. There are two wires coming out of the sensor. The sensor is a small black box secured to the wheel bearing and hub assembly. It monitors the rotation of the rotor and wheel, checking to see if there is ever a stop or break in rotation while the vehicle is moving and the brakes are being applied. If the wires are broken or damaged in any way, your ABS is failing and needs to be serviced by a brake shop. If the wires look fine, repeat this step for each wheel. To check the passenger side wheel, you may need to turn the steering wheel all the way to the left. To check the rear wheels, you'll need to climb under the rear cab.
Turn the ignition off if all of the ABS wires appear to be normal and in-tact at the wheel hub. Wait 30 seconds and turn the ignition back on to the "II" position. If the ABS light remains on, the ABS is malfunctioning. You may have a bad sensor at one of the wheels. You'll need to have this component serviced by a professional brake shop.
