dadcarguy

Hey all,

I just had the brakes completely replaced last weekend to fix a bad warped rotor and bad drum brakes in the back. The new brakes are great, but the ABS light has been on for months. I figured the warped rotor might have tripped the sensors in the front, and had hoped that replacing the brakes would solve the problem...not so. Whenever I start the car and put it into drive and start moving, the ABS light is "off" and there is a "crunching" noise accompanied by strange braking pressure ( this has occured for months). It seems as though the ABS sensors are telling the sending unit to apply pressure when it's not needed. However after just a few minutes of driving, the ABS light comes on and then the car brakes normally. I assume that the ECU is disabling the ABS system because there is a problem with it. There is definatley a malfunction somewhere (damned Fords and their crappy brakes) I just don't know where to start looking. Has anyone dealt with this before and if so, how did you solve the problem? Do I have a bad sensor on one or more of the wheels? Is it the ABS module located near the brake booster? I hope I don't have to replace that, it looks really expensive. I'd really like to avoid a costly trip to the dealer if possible. I'm pretty mechanically inclined and have always worked on my own cars. In fact I've done just about everthing you can think of, except rebuild an engine. Any help you can provide is greatly appreciated.

Thanks, Eric

joe92k1500

My old 01 taurus had a cracked ABS sensor on the driver front wheel. Dealer said this is not unheard of with this car. That might be a good place to start.

dadcarguy

OK....cool. What does the sensor look like?

shorod

It probably wasn't the sensor that was bad, but rather the ring on the axle. There is a brittle ferrite toothed ring around the outer CV joint. The sensor is mounted to the steering knuckle and sends a square wave back to the ABS computer. The frequency of the square wave corresponds to the speed of that axle. The brittle ferrite toothed rings can crack, which causes a larger than expected gap between two of the teeth. The ABS computer sees a glitch in the square wave caused by the larger gap and will set a trouble code.

I would not expect a cracked sensor ring to actually activate the ABS. Unless you have traction control, the ABS will modulate the pressure applied to the brakes by turning the pressure on and off quickly. Without traction control, it won't actually apply added pressure to the brakes. Maybe you have a collapsed brake hose that is not allowing the brakes at one or more wheels to release. The ABS notices the slower wheel(s) and attempts to release that brake, but due to the collapsed hose, you are noticing increased braking? Check the brake pads for uneven wear to see if it appears one brake is wearing faster than the others.

Also, if you can find someone with a professional scan tool and the appropriate ABS software, get the codes read to see what the ABS computer thinks the problem is. The inexpensive scan tools will only read the engine codes, not the ABS codes.

-Rod

dadcarguy

Rod, Thanks for the info. Acutually,I had the brakes completely re-done last weekend, so "pad wear" is not a factor. This isn't one of the nice tauruses, so it doesn't have traction control or 4 wheel disc brakes. I was able to visually inspect the front wheel sensors, and the "notched rings" around the CV joint shaft. I did notice metal shavings stuck to the outside exposed edge of one of the magnetic sensors...found out this can trip the ABS, but I think only if the metal shavings are on the side facing in toward the notched ring. I will investigate the notched rings more thoroughly for cracks or dings when I have time. My next step is to read the ABS code using Autozone's free testing unit. At least that way I can find out what the ECU says.

The only thing that really worries me about this is the "crunching" I hear and feel in the pedal when braking at low speed (5-15mph) just after I start the engine. When braking, the pedal pulsates, but between each pulse there is a very loud crunching sound which slows in intensity as the car slows down. It's sounds almost like something is rubbing somewhere. The car also feels as though it's pulling to one side, or sliding. It's the weirdest thing. However, it goes away as soon as the ABS light comes on. When the ABS light comes on braking is completely normal at all speeds (assuming I don't slam on the brakes). I hope to hell this isn't an indication of a bad ABS control module....those puppies are $500!!, forget labor.

KimMG

How old are the flex (rubber lines) lines in your braking system? These hoses deteriorate on the inside and can cause brakes to lock up or pull. Did the old pads wear evenly?

shorod

I wasn't suggesting that the pads may be the problem, I was suggesting you look at the pads to determine if all four pads were wearing evening. Hopefully the shop that replaced them would have alerted you if they were not wearing evening. Did you mention to the place doing the brake work that you were having a weird noise that you are trying to fix? Was the noise present before the brake job?

If the noise appeared after the brake job, and you still have a pulsating pedal, I'd suspect that some foreign material is trapped between the rotor had and the hub. This will cause a pulsating pedal and is usually accompanied by a strange, loud noise. I wouldn't expect it to go away when the ABS light comes on however, but worth checking.

The code reader at Autozone will NOT be able to read ABS diagnostic codes. You will most likely need to find a shop with an OTC Genisys/Nemisys tool and the ABS software, a Snap-On scan tool with the ABS software, a Mac Mentor tool with the ABS software (same as OTC Genisys), or the dealer. Getting the ABS codes read would certainly help you narrow your search.

If you are in the Cedar Rapids, Iowa area, I would be happy to read your ABS codes (I have the OTC Genisys tool with appropriate software).

-Rod

Jeckler

In my experience, when the ABS kicks in, it does pretty much what you are describing. The pedal will pulsate, and the brakes actually make noise. It's the sheer speed at which the ABS pump works that makes it audible. I'm not sure if the word to describe it is 'crunchy', but, eh.
It might be possible to narrow down which wheel is having issues if you can grab a few friends to meet you in the parking lot. Have each person watch a tire when this happens to see if they can actually see or hear anything.
The reason the light comes on and the brakes return to normal is that the computer sees there's a problem, and disables the ABS system all together, at least until the next drive cycle.
I would guess it's a sensor issue, like was posted above. Even though the sensors (I think they're called Hall effect sensors, correct me if I'm wrong) may look OK, they could be bad, and not sending any data to the ABS computer, which makes it think that wheel is locked up.

dadcarguy

Good point about the pad wear...I did not think to ask about that. However the crunching noise was present before the brakes were done. My guess was that the pads werr definitely wearing unevenly because the rotors were so badly warped. The fact the same exact thing continues to happen everytime I start the car and put it in drive. tells me it's not a brake pad issue, because, as I mentioned before, the crunching noise goes away after the ABS light comes on (which means ABS is disabled) I've been doing research on possible causes. I've learned a lot about ABS over the last few days, thanks to your input. I've also printed some troubleshooting guides. I am going to do a thorough inspection of the wheel speed sensors and the notched speed rings around the CV joints for cracks, imperfections. I can replace the speed sensors pretty easily,and their pretty cheap @$35 each if I need to. I don't know about those speed rings...looks like the whole CV joint/axle has to come apart to replace those...YIKES!! I hope to god it's not one of those.

Anyway, my main concern is that the crunching noise is being caused by a malfunctioing apportioning valve in the ABS control module. If that's the case, I have to replace the whole damn thing, which is gonna cost me $500! just for the part. I figure you were right about Autozone not having the ABS scan tool. I'm gonna have to finsd a shop and throw away $75 to help them pay for their $3500 ABS code reader. Oh well, part of me just wants to ignore this. Who needs ABS anyway? It's dry here in Ca. anyway, and when it's wet I always drive defensively.

shorod

Yep, if the notched speed rings are the problem, the best option is to replace the entire half shaft. If you need to go that route, and decide to do the labor yourself, inspect the new shaft to make sure the ring is in good shape on the new one before installing and make sure the diameter of the ring is correct as well.

As for the ABS control module, if you find that is the problem, you will understand why it is recommended that the brake system be flushed annually. Non-synthetic brake fluid is hygroscopic (readily absorbs water). Once this saturated fluid gets in the ABS control module, it sits there and corrodes the machined surfaces on the many valves and surfaces inside. This causes the module to eventually fail. If you properly flush the brake system annually, and/or switch to synthetic (often times called DOT 4) fluid, you reduce the risk of corrosion occurring. Of course you would want to make sure DOT 4 fluid is compatible with your car before making the switch.

I have installed Speed Bleeders on all my cars to make it easy to flush the brake systems annually, and have switched over to Valvoline synthetic fluid in them as well. I like the Valvoline because it has a higher boiling point than some other synthetics which came in handy when I tracked my sports car.

-Rod

dadcarguy

I found the problem last weekend. The speed-ring on the right front axle is cracked. I moved it into position over the sensor and the ABS light has not come on since. I know that if I hit a pot-hole fast enough, it will probably jar the ring out of place again, so I know it needs to be replaced. The question is, how do I replace this ring? Does the whole brake caliper have to come off to get to it?

shorod

Ahhh, if only it were that easy. The rings are pressed onto the outer CV joint. Probably the simplest and most cost effective way to replace the ring would be to purchase a remanufactured half shaft and replace the entire halfshaft. Not really that bad of a job if you have the tools, a comfortable garage, and reasonable mechanical abilities.

-Rod

dadcarguy

I'll put that off until I absolutely have to do it. Right now the abs isn't acting up. As long as the ring stays put, I'm not worried about it.

Thanks again for your help!