# speedometer wont go over 40mph



## Scenic Lawnscape (Sep 19, 2003)

I have a 99 f-350 4x4 auto powerstroke

My abs light was on and the speedo wasnt working till i hit over 40mph, well yesterday i was driving and it wont go over 40 mph.

So I replaced the sensor in the Rear Diff, and now the speedo works fine untill I get to 40MPH and it wont go any higher.

Any ideas?

This is driving me crazy


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## Bolt-1 (Sep 21, 2008)

I wish i could help you with your dilema. It's always a PITA to have a vehicle prob. and the solution is out of reach. Unless it starts affecting performance, or ends up causing another issue. I don't see the problem. And look at it this way. If it only reads up to 40 mph. Think of the low mileage you'll have in a few years when you sell it.


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## Scenic Lawnscape (Sep 19, 2003)

Bolt-1;848964 said:


> I wish i could help you with your dilema. It's always a PITA to have a vehicle prob. and the solution is out of reach. Unless it starts affecting performance, or ends up causing another issue. I don't see the problem. And look at it this way. If it only reads up to 40 mph. Think of the low mileage you'll have in a few years when you sell it.


the mileage is still working and working and so is the trip counter.


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## Bolt-1 (Sep 21, 2008)

Oh well, wishful thinking for you on my part


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## Scenic Lawnscape (Sep 19, 2003)

Bolt-1;849071 said:


> Oh well, wishful thinking for you on my part


thanks anyways


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## ProScape Canada (Jul 18, 2009)

there are two sensors on your truck. one's in the diff and the other is mounted on your frame. Ones low speed ones high speed and the one in your diff controls your truck shift points.


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## albhb3 (Dec 18, 2007)

but officer my truck said I was only going 40 hahaha


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## Scenic Lawnscape (Sep 19, 2003)

ProScape Canada;849340 said:


> there are two sensors on your truck. one's in the diff and the other is mounted on your frame. Ones low speed ones high speed and the one in your diff controls your truck shift points.


the one on the frame do you know what it is called


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## Scenic Lawnscape (Sep 19, 2003)

i found that there is a sensor on top of the trans but I cant seem to find a away to get it out


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## smoore45 (Oct 27, 2007)

Scenic Lawnscape;850137 said:


> i found that there is a sensor on top of the trans but I cant seem to find a away to get it out


So maybe they changed a few things from 99 to 03, but here is what I think is going on. If your ABS light came on when all of this started then it is a problem with the sensor in the diff. Now that you have replaced that sensor and you are still having problems, it could be the wiring going to the sensor. Did you check that the connector wasn't corroded or damaged? Maybe the seal is getting worn and letting water in it.

The sensor on the transmission is your Output Shaft Speed (OSS) Sensor and is the one that controls your shift points(at least in my 03). Is your truck still shifting a driving okay? If yes, then I wouldn't touch the sensor on your Trans and try to see if you can find something with the wiring on the rear Diff sensor.

Take this for what it is worth, I'm just going off of experience from my 03.


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## RepoMan207 (Oct 7, 2008)

gee, Do Fords not have speed sensors on there hub assemblies?


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## smoore45 (Oct 27, 2007)

RepoMan207;851060 said:


> gee, Do Fords not have speed sensors on there hub assemblies?


Thats a good point. They do in the front, but not in the rear(diff sensor only). If your 99 has 4-wheel ABS instead of just Rear ABS, then it could be one of your front wheel speed sensors(at the wheel end). In that case you may want to get a code checker from Autozone and see if you can figure out which one it is.


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