I have a !996 F150 I-6 I'm not sure about the transmission but it is an automatic with overdrive. It seems that if I drive the truck over a certain period of time that the overdrive light on my shifter will start flashing, and the tranny will start to shift hard. The fluid level is fine. I would like a general direction to start in. One question though, will the PCM keep codes after the truck is shut off? If i turn off the truck and let it sit for a bit, then the overdrive light stays off and the tranny shifts fine. But after a some driving it does it again. Thanks a lot everyone.

 

Yes the codes remain stored. Try to get the codes pulled, it may help to pinpoint the problem.

 

JTIMCORT
Did you ever figure out the tranny issue. OD light flashes and shifts hard? I have the same issue

 

Check the CM stored codes. You may have a VSS code stored.

 

Thanks. HJad the code and changed the sensor long ago. Cleaned the terminals too. Still happening.

 

This is a very common scenario on this forum. Most of us agree the VSS itself rarely goes bad (sorry Brad). To compound the issue the aftermarket replacements tend to create more problems.

Bill is one of the go-to guys for this problem. Here is a link with the keyword search terms "VSS" and "subford": Ford Truck Enthusiasts Forums - Search Results

Plenty of great info in there for how to troubleshoot the issue instead of blindly replacing parts.

 

Mine was intermittent and did not go away until I replaced the cluster with one from the junkyard. I did that about 9 mos ago, no problems since.

 

F250 SD,
If the above question is for your 1999 F250 then the below information does not apply to your truck.

Having the VSS code can be caused by other items than the speed sensor on the rear end.
All the computer knows is that the signal train from the PSOM is not right or it is not getting the train at all.
This can be caused starting at the rear end:
1. By the bearings or tone ring being bad in the rear end.
2. The sensor on top of the rear end broke or its depth being wrong.
3. The wiring from the sensor to the RABS module, bad plugs or wiring.
4. The RABS module.
5. The PSOM, loose parts or bad caps or a bad chip.
6. The speed Control Module.
7. Or even the PCM Computer itself.

The drawing below is for the F-series only as the Bronco is different, the signal from the rear end passes through the RABS module on the Bronco and not parallel to it.


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