ABS light problem - had code read -still no resolution

spederman · Aug 23, 2008

I wrecked my car back in january. Ever since then, my ABS light comes on after about 15 min of driving. And only driving at hwy speeds. It wont come on in city driving or just idling. If i shut down the car, it goes off until i drive hwy speeds again. I cleaned all the abs wheel sensors and found one cracked sensor. Replaced it, but that didnt solve anything.

Today i went in to have to code read at my performance shop. He had a snap-on computer code reader and we drove around to see what codes it was throwing. It said all the sensors are working perfectly and he said the ABS module was fine too otherwise he wouldnt get any readings on the computer.

The only code it was throwing was saying that the front wheels are reading 3-4 mph faster than the rear wheel sensors. I've heard that having different size tires can throw the ABS code, but i've have been running this combination for 2 years with no problems until right after i wrecked it and got the car back. I'm running Nitto DR 305/35/18 rear and 255/35/18 pirelli in front.

Anybody have any suggestion to what my problem could be or what else to check? Think if i adjusted the tire size on my Xcal2, that it might solve the problem of the wheel sensor reading diff speeds?

blubullett · Aug 23, 2008

Throw a tape around the tires and see how much the difference is. If you reprogram it for the right size tires I bet it would help.

BobHyatt · Aug 23, 2008

spederman said:
I wrecked my car back in january. Ever since then, my ABS light comes on after about 15 min of driving. And only driving at hwy speeds. It wont come on in city driving or just idling. If i shut down the car, it goes off until i drive hwy speeds again. I cleaned all the abs wheel sensors and found one cracked sensor. Replaced it, but that didnt solve anything.

Today i went in to have to code read at my performance shop. He had a snap-on computer code reader and we drove around to see what codes it was throwing. It said all the sensors are working perfectly and he said the ABS module was fine too otherwise he wouldnt get any readings on the computer.

The only code it was throwing was saying that the front wheels are reading 3-4 mph faster than the rear wheel sensors. I've heard that having different size tires can throw the ABS code, but i've have been running this combination for 2 years with no problems until right after i wrecked it and got the car back. I'm running Nitto DR 305/35/18 rear and 255/35/18 pirelli in front.

Anybody have any suggestion to what my problem could be or what else to check? Think if i adjusted the tire size on my Xcal2, that it might solve the problem of the wheel sensor reading diff speeds?

You have the data already, now do some math. Measure the diameter of your tire, then compute the circumference as 3.1415 * diameter. Do this for a front wheel and a rear wheel. Now divide the larger by the smaller circumference to see the difference in rotating speed. It might well be that at 30mph the speed differential is not enough to trip a code in the ABS computer, while at double the speed, now it sees double the difference, and that might be out of acceptable variation.

Your XCAL is not going to be able to touch this issue, its a different system. The OBD2 computer doesn't look at those readings, that is in the ABS system. The moral of this is that you can't just throw whatever size tire you want on each end independently, without the potential for this. Why it happened after a wreck is unknown. Did they replace the tires? You may be forced to go to a taller tire on the front to reduce the differential.

Mustang5L5 · Aug 23, 2008

Your rear tire is 26.4" in diamter

your front tire is 25.0" in diamter

That's a 5.2% difference in rotational speed at 60MPH. Higher speeds will cause the difference to widen. 6% is the cutoff for the ABS system I beleive. You are very close, and tire wear can play a role in varying the tire diamter as much as 1/2" which could break the 6% mark.

Mike97gt · Aug 24, 2008

spederman said:
I wrecked my car back in january. Ever since then, my ABS light comes on after about 15 min of driving. And only driving at hwy speeds. It wont come on in city driving or just idling. If i shut down the car, it goes off until i drive hwy speeds again. I cleaned all the abs wheel sensors and found one cracked sensor. Replaced it, but that didnt solve anything.

Today i went in to have to code read at my performance shop. He had a snap-on computer code reader and we drove around to see what codes it was throwing. It said all the sensors are working perfectly and he said the ABS module was fine too otherwise he wouldnt get any readings on the computer.

The only code it was throwing was saying that the front wheels are reading 3-4 mph faster than the rear wheel sensors. I've heard that having different size tires can throw the ABS code, but i've have been running this combination for 2 years with no problems until right after i wrecked it and got the car back. I'm running Nitto DR 305/35/18 rear and 255/35/18 pirelli in front.

Anybody have any suggestion to what my problem could be or what else to check? Think if i adjusted the tire size on my Xcal2, that it might solve the problem of the wheel sensor reading diff speeds?

when ever you have a CEL,ABS or airbag concern always try to post exact code numbers. it make sit a lot easier but this one is easy so nobody needed it

the cause of this problem is the tires.. your rears are a lot taller than the fronts. the abs sees the front tires spinning faster than the rear and thinks this is a fault..

You need to run tires of the same or at least really close to the same overall height for the abs to work.

Tire size programing will not fix this..

As Mustang 5L5 pointed out the abs will set a code and deactivate after a certain percent of difference is detected.. this is part of the abs failure effects management and the xcal 2 can't touch it.

BTW what really scares me on this is why your performance shop could not figure this out.. Does he not know how abs works and why the abs module would shut down abs operation and set a code in this situation

spederman · Aug 24, 2008

Thanks for all the help guys. If the ABS light comes on, is it deactivating the ABS system?

Mustang5L5 · Aug 24, 2008

Yes. When the ABS light is on, the ABS system and Traction control system are disabled

spederman · Aug 24, 2008

One of the tips i got from a guy last nite was to pull the bulb on the abs light. He said the ford ABS system on the mustangs suck and that i have good brakes on my car anyways. I didnt know there were different aspects to ABS systems that make one better than the other. What do you think of this advice?

Mustang5L5 · Aug 24, 2008

spederman said:
What do you think of this advice?

Pull the bulb out? Oh yeah...wonderful advice.

I autocross my GT. I think it's ABS system is one of the better systems I've driven. It kicks in when needed and only as needed. I would say i'm a better autocrosser because of the ABS system. If my GT didn't have ABS, i would have passed it up for one with ABS/Trac control. The 99+ system is redesigned and a true 4-channel ABS system. It's pretty good IMHO.

Now the traction control systemm..different stoty. Unless it's snowing or raining, i turn it off.

Just deal with it until you need new tires. Then get the same diameter tires front and rear. Don't half-ass something by yanking out bulbs or pulling fuses to disable it. Do it right.

97speedster · Aug 24, 2008

When the ABS light comes on it means that the ABS is activated not "de-activated". I had this same problem with my car last year and when I changed the rear tire size to match the front the light quit coming on.

Do you feel a slight vibration when the ABS light comes on?

If so this means that your ABS system is working try to slow down the faster (smaller) tires because it is reading it as traction loss from them. Mine also started after I was re-ended why it chose to start after the wreck I don't know but changing the tires cured the problem.

spederman · Aug 24, 2008

Cool, thanks for all the advice guys. I'll just wait it out till i need new front tires. what size do you think i should go to in front to fix this prob?

Mustang5L5 · Aug 25, 2008

spederman said:
Cool, thanks for all the advice guys. I'll just wait it out till i need new front tires. what size do you think i should go to in front to fix this prob?

255/40/18's will give you a 26.0" diamter which is 0.4" smaller than your fronts. That size will work fine.

There may be other sizes you could use too if you wanted to go wider.

Play around with this
Tire size calculator

blkhorse · Aug 25, 2008

97speedster said:
When the ABS light comes on it means that the ABS is activated not "de-activated".

Huh? whenever the yellow light for abs is on,it means the computer sense's a problem and disables the abs...light on,no abs

97speedster · Aug 25, 2008

blkhorse said:
Huh? whenever the yellow light for abs is on,it means the computer sense's a problem and disables the abs...light on,no abs

Go drive your car and slam on the brakes and tell me if the ABS light comes on. ABS will start pulsating to slow the tire speed down safely (activated). The light comes on to let you know that the system is activated. And if you continue to keep driving with the light on the more the pulsating increases to try to slow it down. Damn near feels like the car is going to shake apart. Personal experience on this one. Code kept telling me both rear sensors were bad but I tried changing the tires first and code never came back and light never came on and pulsating disappeared.

blkhorse · Aug 25, 2008

no mine does not come on during an abs event,the only light that comes on when active is the traction control. I have not seen any abs equipt car where the light comes on when in an abs event,assuming no abs problems

97speedster · Aug 25, 2008

Traction control has nothing to do with ABS. Just because your light for traction cobtrol works that way doesn't mean that your ABS does. Do some more research.

blkhorse · Aug 25, 2008

97speedster said:
Traction control has nothing to do with ABS. Just because your light for traction cobtrol works that way doesn't mean that your ABS does. Do some more research.

WRONG,I am not the one that needs to research,give it a try

Mustang5L5 · Aug 25, 2008

97speedster said:
Go drive your car and slam on the brakes and tell me if the ABS light comes on. ABS will start pulsating to slow the tire speed down safely (activated). The light comes on to let you know that the system is activated. And if you continue to keep driving with the light on the more the pulsating increases to try to slow it down. Damn near feels like the car is going to shake apart. Personal experience on this one. Code kept telling me both rear sensors were bad but I tried changing the tires first and code never came back and light never came on and pulsating disappeared.

Um...no it doesn't

Hate to break it to you, but what you just described sounds like a problem with your ABS system. That's NOT how it should work at all. You might want to try to fix that.

This is not a Mustang thing. That applies to ALL vehicles. The ABS light comes on during startup to tell you if the bulb is functional and then shuts off until a code is stored in the system. When a code is stored, the ABS light comes on and the system is disabled. During ABS use, the light DOES NOT come on at all. You will never see the YELLOW ABS light at all UNLESS something is wrong.

The traction control system (which is part of the ABS system BTW) does display a spinning wheel when the system detects wheel-spin and activates. That's also not a Mustang thing...all cars equipped with TCS do it to tell you if the system activates.

If you are braking hard, activating the ABS and the light comes on, that means your system is finding a fault somewhere during use and deactivating itself. Also, the car shouldn't feel violent during ABS use. Other than the brake pedal vibrating, the car should track and drive fine with no vibration in the car itself.

I'm not trying to be a jerk here...but your ideas about how ABS systems work is incorrect

PS. If the red BRAKE light comes on during hard braking, it means you are low on brake fluid

ToplessStang · Aug 25, 2008

spederman said:
One of the tips i got from a guy last nite was to pull the bulb on the abs light. He said the ford ABS system on the mustangs suck and that i have good brakes on my car anyways.

Let me give you a tip, don't EVER take car advice from that guy again .

spederman · Sep 25, 2008

UPDATE: I ended up getting some different size profile tires for the fronts. I got 255/40/18's and that fixed my problem. No more ABS light

ABS light problem - had code read -still no resolution

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