Antilock problems 2003 FXII

[sonicblue]

I've been noticing a progressively worsening problem with my antilocks. Whenever I make the slightest turn at low speeds and come to a complete stop, the antilocks will kick in. For instance, pulling into a parking spot will cause them to kick in. I'm obviously going less than 5MPH, and barely turning the wheel sometimes like into an angled spot, or just going into a median turnaround. It seems that it only does it making left turns which seems very strange. I did go to 33" tires years ago and reprogrammed for them, but this has only started in the last year or so and seems to be getting worse. Any ideas?

Darryl

 

[04 EDGE]

one of your front wheel speed sensors is bad. you need a live data scanner to see witch one it is.

 

[sonicblue]

Thanks 04 Edge. That was my guess but I wasn't sure. I have an Actron CP9185 so I assume this will work for the logging?

Darryl

 

[04 EDGE]

you need to look at ABS live data. there will be no codes. what will happen is this, one of the sensors will "drop out" at 5mph and read 0 mph while the other two (front and rear) will read normal.

that is the bad sensor

 

[sonicblue]

Thanks again. Unfortunately my CP9185 won't read wheel speed sensors, so I have a CP9449 on order. Hopefully this will narrow down the faulty sensor.

Darryl

 

[04 EDGE]

this i can tell you, its one of the front sensors.

i have replaced to many of them at work, i got one going bad, but i am to lazy to deal with it.

 

[sonicblue]

Yeh, I've been putting this off for a year as it hasn't been any big deal since I know what to expect. Still that momentary loss of braking power right at the last second has gotten a bit exciting at times :-O

I should have the scanner in a couple of days and will let you know what I find. I'll focus on the front sensors since your confident this is where the problem lies.

 

[sonicblue]

Well, I got the CP9449 in today, and although it says "diagnoses wheel speed sensors" they mean it only shows trouble codes. It can not do real time monitoring. Oh well. I may try to tap into the wiring and put my oscilloscope on the signals to figure out which one is dropping out.

 

[afdoc]

what do you notice?

Just out of curiosity, what do you notice with the vehicle when this happens?

 

[Jspafford]

For the price you paid for the reader, you could have had it done at a dealer and been fixed.

 

[sonicblue]

Just a quick update.

I sent the scanner back as it was useless to diagnose this problem. The service manual gives an AC voltage reading on the sensor when spinning the tire by hand, so as soon as I get a fee moment I will run this test to isolate the bad sensor.

afdoc,
You can feel the ABS coming on in the pedal as it pumps and slightly sinks under your foot. If you don't expect it, it can be surprising as it takes you longer to stop when this happens.


It is still getting progressively worse as for the first time it came on the other day when I came to a straight line stop.
Darryl

 

[lowrider961]

Now I think I know whats wrong with my brakes now thanks everyone.

 

[desertrat]

If the ABS system is making the vehicle dangerous, pull the fuse until you get it fixed. The vehicle just reverts to standard brakes, I drove for 40 years before they invented the damn things. Not that they are not good under the right circumstances. I had a 1 Ton GMC that acted as you describe and neither the Dealer (it was warranteed at the time) or me ever figured it out.

 

[sonicblue]

I finally got a chance to look into this problem more. The shop manual says you should get a minimum of 100mVAC out of the sensors when spinning the tire by hand. Of course it didn't say how fast to spin it, and since the voltage is speed sensitive, I found this odd. Regardless, spinning about as fast as I could by hand, I got about 20mV out of the left sensor, and about 45mV out of the right. This confirmed my suspicion that it was the left sensor although the right was not much better.

While trying to get the left sensor out of the hub I broke it, so I had to get a new one regardless. (my local ford guy got me one way off the $220 list price, just $150. yikes!)

I live in Michigan, so the mounting flange on the hub had a fair amount of flaky rust on it. I cleaned this all off, and put the new sensor in. What a difference! Barely spinning the tire and I was getting over 200mV! So I decided to look at the other side. I was able to get this sensor off without breaking it (just keep rotating it while you gently pull up). I cleaned the rust off it's flange, replaced it, and now I get almost 200mV out of it while barely spinning the tire.

The final result is, the rust between the hub and sensor was pushing the sensor slightly up, and since it is a very critical gap between the sensor and tone ring for proper operation, especially at lower speeds, it needs to be cleaned and properly mounted.

Darryl

 

[brock71]

Front wheel speed sensor

This thread is EXACTLY what I have been noticing on my 2001 Ranger. Left hand low speed turn has the antilock kicking in unexpectedly.
What is involved in cleaning th erust off the hub?
How much disassembly?
John