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2008 Taurus output speed sensor

Having a problem with our low mileage 2008 Taurus. When on the interstate and it gets up to 70mph, dash goes bezerk–can’t get any info–no speed, gas gauge, etc. (Doesn’t have this problem around town.) After this, when the car comes to a stop, it takes it forever to get back up to speed. Took it to trusted small town mechanic who knows what he is doing–he says car didn’t show any codes. He felt the computer was out of whack and straightened that out. He said if that didn’t work, take it to the transmission place in nearby larger city. He feels it could be the OSS.

Transmission place can’t find anything wrong. Says car shows no codes. I am 99% sure no one drove it on interstate. Place has a great reputation but is understaffed.

Take it to the Ford dealer. They kept it over a week–and guess what??? They couldn’t find anything wrong with it and it showed no codes. When I go to pick it up I am not happy with the shrugged shoulders and ‘we can’t find anything wrong with it’ answer. I ask if anyone even drove it on the interstate. Eventually manager comes out and goes for a ride in it with my son. Within 2 minutes of it being on the interstate it does exactly what we have been saying it does. Manager comes back and tells guy at desk it is the OSS and the engine is misfiring. I hear him say that when the car stops, it still thinks it is in 4th gear.

After over 3 weeks at dealership and lots of excuses and missed promise dates and what sure sounds like outright lies, nothing has been done to car. I pick up car and we go back to transmission place because we feel they really are our best option–great reputation.

Message there is that it could be OSS itself, the wiring, or the computer–there’s no way of knowing. We call another Ford dealership in another town–they say they won’t work on anything that doesn’t throw a code. They want to replace the whole transmission.

What do we do? This has always been a dependable car and son needs it for work. Please advise.

I had a speed sensor fail completely in my Lincoln about 6 or 7 years ago and no codes were set.
Testing the speed sensor externally from the car indeed showed it was dead as a door nail. Replaced the sensor and all was well.

Replace the whole transmission? Wow. Seems a bit extreme for wild guessing.

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So why can’t the Ford dealer put a mechanic in the car with a scanner plugged in reading the data so they can prove the OSS is bad rather than the service manager guessing that is the problem?

You need to find a better mechanic. These guys couldn’t find their rears with both hands, a flashlight and mirrors!


Apparently there is a shortage of all types of mechanics in our area–industry is booming and mechanically minded folks are finding better jobs there. Area also full of high tech companies–area is infested with engineers but tradespeople are scarce. Forgot to add I called another Ford dealer and they didn’t even have a transmission person–they recommended the transmission place that was our original 2nd stop. That trans place is a one man operation and that guy says he can’t find anyone who wants to do the work or even wants to learn to do the work. He will do what he can and then just retire one day. Someone else told me that the Chevrolet dealer–which is a huge operation–shares a single diesel mechanic amongst three locations. Have been to or contacted Ford dealers in my small town and two cities and can’t seem to get help.

Based on those comments, you will not be able to fix your car because you are convinced you have no other repair shop options. We can’t scan data for you and in the absence of data, any attempted repair will be a guess. And replacing parts on a guess can be very expensive and a total failure.

We don’t know where you live but if you can’t find a mechanic that can handle this repair seems you have only 2 options. Travel as far as you need to find a mechanic that can work on the car or scrap the car. Sorry.

Everyone agrees that throwing parts at a repair is not the way to do things,
BUT given the cost of output sensor at around $30 + (from rock auto)
and lack of help from presumably expensive “diagnosis”, I’d chance changing the part.

Had one trans sensor die, and replaced it myself in an '86 Taurus, many years back, symptoms were like yours, also strange dashboard lights (digital dash), poor acceleration, surging, and IIRC, some backfiring.
Also, these sensors often work on magnetism, and older transmissions often shed magnetic (steel) debris. Maybe you can pull sensor and see if its coated with “iron filings” if so, just cleaning it up can fix things for a while. Good Luck !!

It’s time to take a shot. The least expensive and highest probability cause is the OSS. I’m guessing no one has changed it because you’re sending message you want definitive diagnosis before work is done. If I went to this shop and heard this-

I would have told them to go ahead and replace the OSS. Authorize the repair and remove any liability on their part.

Thanks everyone for the tips. At least I know how to talk like I have a clue about this now when I call about the problems. I think I will call the local guy that ‘everyone’ uses and talk with him about trying to replace just the sensor. We were quoted about $4,000 for a new transmission at a Ford dealer. Car only has about 98,000 miles on it so needing a new trans seems questionable. If needed I will ask around locally and get recommendations of other places. I live in North Alabama and largest city nearby–Huntsville–is where I assume we would have to go. We would likely have to have it towed there. Traffic there is crazy even on a good day and I’d not attempt it in this car unless I went at 2 a.m. Any good mechanics looking to relocate please look at everything within a 45 minute drive from Huntsville. We’d love to have you!

I presume they mean they won’t work on a problematic speed sensor until it throws a code. They’d fix a flat tire without any codes, right? I’m guessing they’ve run into this problem before, spent a lot of diagnosis time, and never figured it out, never made enough $$ to recoup their time investment. So that’s why they now won’t work on it.

hmmm … well they’d work on it I bet if you ponied up $2000 beforehand, and told them to bill you by the hour, and you’d pay them whether they fixed it or not. So that’s one option. I think however the advice above to simply replace the speed sensor is the way to go. It’s apparently a relatively inexpensive part. Ask them what the labor fee is though, as it might be difficult to replace.

The other option is to use a lab o’scope to monitor the sensor’s signal voltage output vs time. With the car on a lift, wheels spinning. It’s a hall-effect device. the way it works is electrons travel along a semi-conductive path inside the sensor. Moving electrons are subject to a force when there’s a magnetic field present. So when the magnet comes by as the shaft spins the resulting force moves all the electrons to one side of the path, and that produces a voltage. When the magnet moves away the electrons return to the center of the path, and no voltage. So an o’scope can monitor that voltage as the wheels (and output shaft) spin. It should produce a clean square-wave sort of signal. If the square wave isn’t so square, or gets less square the faster the wheels are spinning, that could indicate a problem with the sensor, the magnet, or the distance between the two.

Modern hall effect sensors have the magnet inside behind the sensor. The reluctor wheel is just ferrous metal.

However, they are typically very sensitive to gap distance as you mentioned. I just fixed an issue where abs was kicking in at speeds below 8 mph on my truck. The right wheel speed sensor was weak and dropping out. Rust scale lifted the sensor and increased the gap enough to affect it.