Please give your two cents... Code P0731 Could it be caused by a Speed Sensor? - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 06-19-2012
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Icon4 Please give your two cents... Code P0731 Could it be caused by a Speed Sensor?

Hey Everyone,

My 05 Ford Ranger XLT 4.0 V6 Automatic has an issue.

I was on the highway and I went to pass a car and the truck did not accelerate.

Manual 1 works.
Manual 2 works.
Drive Engages... will creep forward if truck is over 3-3500 RPM only.
Reverse Engages... will creep in revese if truck is around 3,000 RPM.
Park- As usual.

OD OFF Light flashing.... AAMCO diagnosis: Need new transmission 1st gear totally gone. Clutch band must be shot. They never dropped the pan. Only ran computer scan. Code: P0731.

Now if there was no first gear left, wouldn't Manual 1 not work at all? I'm not sure, since i'm not too smart on transmissions.. please let me know!

P0731: Incorrect First Gear Ratio.

If you are in Manual 2 and downshit to Manual 1 there is Engine Braking occuring.

Recent Services:

Oil Change, Tire installation. 255/70/16 to 265/70/16.

Issues with tires: vibration/shaking in truck. I believed it was tire balance issue it appeared at highway speed 55-70mph.

So lets go to it already right?

Here is my theory.... I was online looking up codes and transmission problems..

Could it be the Speed Sensor (Transmission)?

Why do I think this?
Transmission Speed Sensor talks to the rear differental sensor. Speedometer in truck works. The speedometer works off of the rear differental senor right?

So if the Transmission TCM is not getting the information of how fast the truck is going, it would mess up a shift and engage the truck in limp mode right? I'm thinking that is what I am stuck in.

I was going to quickly change the Transmission Speed Sensor tonight, but no parts store had one in stock. After installation I was going to leave the battery disconnected for 30 minutes to let the computer reset.

My thought process is that the TCM is not getting the actual speed. Now after I had the new tires put on (larger) I noticed to accelerate I would have to be near 3,000 RPM. Usually I accelerate with the BG Goodrich MT's in 255/70/16 at 2000-2500 RPM. I'm starting to wonder did the change in tire size trick the shifting in the truck? Or could this be a Speed Sensor?

Also, maybe it really is a tranny problem and it needs to be rebuilt.

Please guys, Let me know your thoughts I'm bringing it to another transmission shop tomorrow for diagnosis. They are a smaller place that does rebuilding on site, and they do transmission repairs too.
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Old 06-19-2012
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An O/D light flashing with those symptoms sounds like a bad transmission.

I would have the second shop look at it. I think they are on the right track there.

The speed sensor being bad would reflect more on your speedometer. not your shifting.
Your tires are well within an ok range for your transmission, especially with 4.10 gears.
Check your transmission fluid. is it burnt?
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Old 06-19-2012
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My transmission fluid is still red. It was last flushed out around 60k miles. I was going to have it done this week!

The fluid has a little dirtyness too it but jsut slightly. I dont' believe it is burnt. It's not black. It doesnt stink terribly. It was a small odor to it, nothing too strong.

Doesn't the rear differential speed sensor control the speedometer? If the rear one goes out the speedometer will not work. But as I was reading if the transmission on (output?) goes out the speedometer may not show signs.

There isn't must info on this, so i'm picking brains :)
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Old 05-08-2017
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HELP!!!

This exact same thing is happening to my truck right now. Did you ever get it fixed? What was it? I know this thread is like 9 years old but I hope you are still on here!
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Old 05-08-2017
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Sorry about the typo. I meant 5 years
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Old 07-04-2017
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Input speed sensor

I have the same issue will be looking at it tomorrow evening.
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Old 07-12-2017
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Same thing just happened to me.

This just happened to me today. Please post if you found a fix to the problem.
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Old 07-23-2017
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Hi everybody.
I have the same trouble. The code I get is P0715 input speed sensor turbine. This speed sensor is reported to live on the very top of the transmission. I have been looking for ways to get to it to fix it. It is driving me nuts. I replaced the output speed sensor because that is all that comes up when you look this up. The out put is your speedo and tach. The one we need fixed is the one in front that takes info in coming into the transmission. Yes it drives bad excelleration is little.

Anybody for help please. I'm not alone here. Guys above me this is most likely your issue as well.

Jim

Last edited by New2Ford; 07-23-2017 at 02:01 PM.
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  #9  
Old 07-27-2017
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Mechanically, I had the exact same problem in my old truck. D and R didn't work, 1 and 2 did, O/D light was blinking. From the research I did, it was a bad transmission. I replaced the tranny, and all was well. We figured that it might have been something called a sprag unit, I believe. Based on the symptoms listed above, that's what we decided it was. Point being, transmission was junk. I pulled one from a truck at a junkyard for $300 and swapped it out. We had had the battery disconnected for about a month, so when we put it back on, the computer was all confused. A few O2s, pcv valve, cleaned IAC, and TPs later, all was working.

It makes me sad to think of all the work I did to that damn truck just to get a new one :/
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