ABS, Speedometer, & Cruise

new 4/20/2004

Every now and then when cruising down the highway, my speedometer will
suddenly drop off, then come back. Sometimes it's just for a split
second. On rare occasions, it will stay off (read zero) for quite some
time.

When this happens, if I'm using the cruise, then the car will start to
accelerate.

The ABS light sometimes comes on, especially in cold weather. However,
the ABS light coming on does not seem to have a direct correlation to
the speedometer issue.

What could be causing the drop in speed readings? What could be causing
the ABS light to come on? Could they be related?

I've heard that the ABS system and speedometer are tied together. But I
don't know what to go looking for. Anyone have any ideas?

Curtis Spears

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I had a similar problem with my 97. Last summer, the ABS light started coming on when the weather was extremely hot. I noticed that when things cooled off a little bit, the light went out. I also learned by trying, that when the ABS light was on, I had no ABS and when it was off, the ABS functioned normally. It never did set a diagnostic code. I just put off working on it until one morning when the speedometer quit. When that happened, it affected shifts, power steering, and I can't remember what all else.

In the 96 and 97's, the ABS module develops the speed reference signal that the whole car uses - including the speedometer. I'm not sure if that holds true for the 98's and 99's. My parts research taught me that the 96 ABS control module is unique to the 96 SHO and the 97 is unique to the 97 SHO. I THINK that the ABS control modules were the same for all of the 98 and 99 Tauri - SHO and SLO.

In my case, I got very lucky. After I had the ABS unit out of the car and the control module separated from the pump side (twisted off a bolt in the process), I could see through the clear gel they have poured over the internal circuit board and could see that there were small wires connecting the circuit board to the plug terminals. Nothing was visibly wrong but when I poked a small screwdriver into the gel and worked the wires around a little bit, I discovered that three of them were either broke from the plug terminal or were so weak that they broke when I wiggled them. It was a little tricky but I picked enough of the gel out to clean things up and solder the wires to the terminals. That has now been about 20K miles ago and it still seems to be okay. I'm keeping my fingers crossed.

My bet is that you have a similar problem and that like mine, temperature changes are enough to make the wires move enough to make or break connection.

Dave Witte
97PG Welded

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Dave,

What you describes sounds very familiar. I have noticed that when the speedometer starts to act up, multiple systems are affected, most noticeably the cruise and transmission.

Maybe you can answer some remaining questions for me: how many speed sensors does the ABS system monitor? One for each wheel?

Where are the speed sensors located? Where is the control module located?

Can you recommend how best to troubleshoot this system?

Is there anyplace than can read the ABS trouble codes other than Ford dealerships?

Thanks again.

Curtis

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Reads 4 on this car. The fronts are part of the outer cv joints.
The sensor is in the knuckle, the backs are part of the wheel hub and bearing assembly
the sensor is mounted on the rear hub knuckle. The control module, relay and pump motor is mounted right below the battery.

Check first for broken worn wires are the sensors, rust build-up, dirt, mud, snow etc will change the airgap and throw a code. Cracked exciter rings will cause a code.

Any shop with a SNAP-ON MTC{model number here} with an ABS card for it can read the codes.

Mine has only come on once in 4 years and the RR wheel was the code and it was packed full of snow. drive thru car wash with underbody spray fixed the problem due to the garage at home being full.

Now there a different wiring diagram from the 96 to 97 model year for this system. I have not looked at them to see what the difference is.

The SHO uses the RF ABS sensor as the Vehicle Speed sensor vs the Regular Taurus using the Speed Sensor in the Transmission.

Clare

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