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Old 06-09-2006, 01:09 PM   #1
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Default ABS false modulation problem

I have a pretty frequent false modulation (abs kicks in) with my 02 SE Bonne - wondered if this happens with anyone elses cars and if anyone has ideas what I can try to fix it. Haven't found anything similar described in other threads.

Basically my ABS kicks in (feel it in the Pedal) at upper speeds (40-70mph) when I lightly or mildly apply the brakes. As I apply more brake pressure and they're on strong, it does stop modulating. One day I had the back seat removed and I could hear a buzzing in the fuse/relay panel when it happened. I thought maybe by touching the relays when buzzing, I could determine which valve might be modulating (?)

Will be glad to try providing any other information or doing tests if someone thinks they might know what'* going on!

Thank you.
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Old 06-09-2006, 09:12 PM   #2
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Default Re: ABS false modulation problem

Quote:
Originally Posted by Woody_02SilverSE
I thought maybe by touching the relays when buzzing, I could determine which valve might be modulating (?)
All solenoid valves, along with the pump motor are contained within the Brake Pressure Modulator Valve (BPMV). I don't believe there are any relays back aft associated with ABS. Are there any faults reported by the Driver Information Center?(DIC) ABS light I asssume is not lit?
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Old 06-09-2006, 10:00 PM   #3
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Default Re: ABS false modulation problem

Quote:
Originally Posted by markwb
I don't believe there are any relays back aft associated with ABS. Are there any faults reported by the Driver Information Center?(DIC) ABS light I asssume is not lit?
No faults or ABS light so far. I could be wrong about the noise coming from the aft fuse/relay panel when it kicked in, just what I thought I heard. BTW I had all 4 wheels off last weekend and inspected the sensor plugs, gave them some dielectric grease.[/quote]
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Old 06-09-2006, 10:24 PM   #4
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So, no "low traction" indicator when this occurs? Could you perhaps be experiencing the effects of warped rotors instead of an ABS problem?
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Old 06-10-2006, 12:25 AM   #5
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Quote:
Originally Posted by Archon
So, no "low traction" indicator when this occurs? Could you perhaps be experiencing the effects of warped rotors instead of an ABS problem?
No "low traction" indicator either. Does one or the other always light up when ABS or traction control comes to life? Hadn't thought of the possibility of warped rotors. I can't say I've ever had a vehicle with warped rotors so I'm not sure how to tell it apart. It feels like the ABS pulsation I've experienced in the pedal of other vehicles. Haven't driven this car in the snow yet, so I don't know for sure, now, what the ABS sounds like.
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Old 06-10-2006, 12:30 AM   #6
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I don't know if it'* related but I had a vibration when starting out after a turn and it felt like driving on snow chain marks on asphalt. I think it was the stability system applying the right front brake. No stability system active indicator in the DIC though. I stopped and checked for low tire and restarted the car and no more problem. But after that I had a couple of Service Stability System indications on different drives at low speed turns.

My wife complained of serveral Service Stability System messages driving in the rain one day. So I'm going to check connectors at the wheels. Especially the left front because I did go around and open all the brake bleeders to replace the brake fluid prior to this happening.

Could it be your stability system? I had the steering wheel sensor replaced under warranty last fall before warranty ran out.
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Old 06-10-2006, 02:45 AM   #7
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perhaps this is related.. just throwing darts here, but this recall was news to me, it may affect your car

http://www-odi.nhtsa.dot.gov/cars/pr...0&summary=true
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Old 06-10-2006, 02:58 AM   #8
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This is the description of the low traction light....

LOW TRAC Indicator
The LOW TRAC indicator is controlled by the instrument cluster via class 2 serial data messages from the EBCM. When the ABS, TCS, or VSES is active for 0.5 seconds, the EBCM commands the instrument cluster to turn ON the LOW TRAC indicator.
The LOW TRAC indicator will also turn ON during the instrument cluster bulb check. When the ignition switch is turned to ON, the LOW TRAC indicator will turn ON for approximately 3 seconds and then turn OFF.

So, it should come on when the ABS kicks in. I can't say for certain without actually driving your car, but I would guess that you have a warped rotor problem based upon your description. I'd suggest having the rotors turned or replaced and see if the problem persists. Or you could take it to a brake shop and have them diagnose it.
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Old 06-10-2006, 11:04 AM   #9
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Quote:
Originally Posted by Archon
This is the description of the low traction light....
I can't say for certain without actually driving your car, but I would guess that you have a warped rotor problem based upon your description. I'd suggest having the rotors turned or replaced and see if the problem persists. Or you could take it to a brake shop and have them diagnose it.
Thanks everyone I think the rotors are a good possibility. Which means my whole thread title would be wrong Today I'll pull the ABS fuse if there is one and see if it still does it.
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Old 06-11-2006, 12:07 PM   #10
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Thanks for the suggestions. I've rethought pulling the ABS fuse (I don't want to set an ABS code and have the light stuck on). Will investigate the rotors first. Anyone know the odds of problems with front vs. rear rotors, or how to determine which might be warped (or have brake-lining buildup) if that'* the problem? I can't feel anything in the steering wheel or tell by the sound.
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