2006 Mercury Mariner: ABS brake problem

Old 03-09-17, 08:15 PM
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2006 Mercury Mariner: ABS brake problem

I've got a 2006 Mariner SUV. Not long ago, the brakes began to fail when applied, and give the ratcheting type of feel that the ABS system does when sliding on ice. But then the brakes start working again. I also noticed the ABS light comes on for a while and then goes off again. I've not been able to find an auto parts place that will read the ABS error code, so I haven't got that info available yet. My first thought was that there was a problem with the ABS sensor, but not really with the brakes. However, I've noticed over the last couple of days that the brakes seem to work correctly when the ABS light is on, but not when it's off. Any thoughts?
Old 03-09-17, 09:01 PM
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Welcome to the forums.

Most of the chain auto parts guys should be able to read brake codes.
PEP Boys does here near me.

I bought a $150 scanner that reads OBD II and brake codes.

In reading up on your vehicle it appears that there are several known problems.
One is a cracked/defective relucter gear (tone ring) on the axle.
Another is a defective wheel sensor. Basically the ring has magnetic poles on it that the sensor picks up.

A code scan is a must before anything can be done.
Whether the ABS light is currently on or off..... the code(s) will be stored.

Name:  tone ring.jpg
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The red arrow is pointing to a crack in the ring.
Old 03-10-17, 12:12 AM
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So a little more detail:

Regardless if there is a tone ring or encoder ring, the sensor picks up the on/off signal generated as it spins. If the ring has a missing tooth (as in the picture) or a bad magnetic segment on the encoder ring the computer senses that and assumes the wheel is sliping and activates the ABS. Repeated failures is where the code and light come from.

Best hope is a bad wire/connector, sensor, or tone/encoder ring.
Old 03-10-17, 05:49 AM
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Thanks for the info. I'll look for a PEP Boys near me. I was hoping to not have to fork out for the scanner myself, but hopefully they'll let me use a store unit with the motivation that I'll buy the parts that are necessary from them.
The fact that the brakes seem to work better when the ABS light is on is still confusing to me. If the brakes themselves are actually bad, will the ABS function initiate to help the failing brakes? That doesn't seem likely to me, but I don't really understand how the ABS mechanism works.
Old 03-10-17, 05:55 AM
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A little more info... if this this is important. The brakes typically produce the "ratcheting" failure feeling when I first start driving (especially in reverse), and then start working better after the car warms up.
Old 03-10-17, 08:58 AM
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The ABS light will come on when a fault in the ABS system is detected. Generally, when the ABS light is on, the car has also deactivated the ABS system because it's not working right. So your brakes are functioning as normal, non-anti-lock brakes then. Basically, if the light is on, ABS is off.

ABS constantly evaluates wheel speed (determined from the sensors and rings the others have mentioned) and uses that data to determine if there is wheel lockup is occurring, which leads to poor braking performance. It then applies and releases the brakes for you, getting you just to the point of wheel lock and then releasing the brakes to get them rolling again. This happens many times per second. That's the "ratcheting" or pulsing feeling associated with ABS.

Something's probably going on that's causing ABS to think wheel lock is happening, so ABS activates. It's then realizing that something isn't right, turning on the ABS light, and deactivating the system -- making the car act "properly" again.

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