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Fluctuating speedometer and ABS light

I have a 1999 Ford Explorer Sport. In the past month, I have experienced on a number of occasions a sudden fluctuation in the speedometer. At the same time, the ABS light will come on and the engine becomes loaded. This will last for a second and then return to normal. The interval between occurrences is not fixed or repeatable but often occurs when traveling at a higher speed (65-70 mph) on the interstate. The first garage said it might be the idle valve so we had it replaced but the problem appeared again a few days later. We just recently took it to a Ford dealership that said it might be the rear wheel ABS sensor so we had this replaced. Once again the problem reappeared a few days later. Has anyone had a similar problem? If so, what was done to fix the problem?

I have not had a similar problem.

Whomever said this was an idle air control valve should just hang it up. That’s ridiculous.

A rear wheel ABS sensor is slightly less silly. How did someone arrive at this diagnosis?

The very first thing that all of this points to is a problem with the vehicle speed sensor (VSS).

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I’m in Cig’s corner. VSS was the first thing that popped into my head after reading the symptoms, Joey.

Check the wiring to the VSS before replacing it. Intermittent problems are most likely due to bad connections than bad sensors. The VSS is a simple hall effect sensor, and typically they either work or they don’t. It is a magnet wrapped by a coil. The tone ring passes spurs of metal by the magnet, and the coil will generate voltage pulses at the speed the metal passing by the magnet. The computer reads the speed of the pulses and determines the truck’s speed.

Even thought the connections are designed to be water tight, 12 years takes a toll on things, and those connections may have just enough corrosion on them to give you problems like this. Sometimes, simply unplugging and re-plugging the connector is enough to clean the connections. I prefer to use an electronic cleaning spray on both the pig-tail and sensor contacts if I’m going to go to the trouble of crawling under there.

I have a 2000 Explorer, and had a problem with the tachometer dropping to zero intermittently. Pulling out the gauge cluster and cleaning the connections to the tach on the backside of the cluster fixed the problem.

Thanks. We also did some digging around on the internet and like you guys said, most pointed to a problem with the VSS. Thanks BustedKnuckles for the detailed info on the wiring to the VSS; we’ll try that first.

Update and more questions: We took the explorer to the Ford service center and they said the VSS and ABS were a single unit, which they had replaced. We still have the same problem so they said they double checked all the wiring and connections and there was no loose wiring or corrosion; nothing to indicate a problem with the connection. They were able to duplicate the problem but their computer was unable to find any problem codes when they checked. We don’t know if they checked the actual signals at the car’s computer from the VSS. We’re at the point where one course of action is to replace the power control module or other items without a clear diagnosis; clearly this is a potentially costly path with no guarantee of a fix. Does anyone have further suggestions on how to diagnose where the problem is? Thanks.

Was this ever solved?

@Joanna_Cummings- Joanna, the person would started this has been inactive for 4 years. It would be best to start your own thread so replies will be for your problem what ever that may be.

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