E40D OD Off light flashing

[BKahler]

I need help trying to identify the source of a problem.

Our 92 F350 has the 7.3 IDI with the E40D transmission. The transmission was rebuilt with ALL of the latest updates about two months ago. The only issue I have had with the transmission is harsh shifting. At first I thought that’s the way it was supposed to be but I've come to the conclusion that there is probably something wrong.

What I'm wondering is if an issue I'm having with the tach (speed sensor?) might actually be the cause of the harsh shifting. When first starting up the truck after it sits for more than a few hours the tach registers 0 when at idle. If you tap the pedal the tach registers what I believe is the proper rpm. Once you release the pedal it goes back to 0. This condition exists for probably 20 minutes or more. During that period if you come to a stop the tach will go to 0. Anytime the tach is at 0 rpm and the transmission is in Drive the OD Off light on the shift lever starts flashing. Once you accelerate the tach starts registering rpm and the OD Off light stops flashing.

So my question is, will this problem with the tach or speed sensor cause the E40D to go into limp mode and remain there even after the sensor starts working properly as you continue to drive?

Is there anything difficult about changing out the tach sensor or anything I should know before attempting the sensor replacement?

Thanks!

Brad

 

[pafixitman]

Brad...short answer is yes, that is most likely the cause. Easy to swap...big nut to the right of the IP.

 

[BKahler]

Brad...short answer is yes, that is most likely the cause. Easy to swap...big nut to the right of the IP.

Joe, I think the big nut is actually behind the steering wheel in this case....

Thanks for the info. I guess I need to track down a replacement tach sensor and install it. Can I assume that it's just a matter of removing the big nut by the IP and replaceing it with another one and then hooking the wires back up?

Do I need to somehow clear the error code in the transmission or will it automatically clear itself once the new tach sensor is installed?

Thanks again!

Brad

 

[pafixitman]

You will need to clear the codes. Either get the scan tool (about $30 from autozone, walmart) or disconnect the batteries for about 15 minutes.

 

[BKahler]

Is the reader you're referring to the ODB-2 reader? If so I have one of those. If not then I'll just disconnect the battery for a while and give that a shot.

Thanks for the info!

Brad

 

[BKahler]

pafixitman,

I got the sensor replaced and due to extenuating circumstances left the battery disconnected for slightly more than 45 minutes (36 hours actually!). Finally had a chance to start the truck up and the tach now registers at idle when I first start it when it never did before. Took it for a test drive and the shifting is a LOT better. You can still feel the shifts taking place but nothing like the kick in the pants, neck snapping shifts that it used to do. I'll be making a trip with my gooseneck trailer next week and will see how much difference it makes while towing.

Bottom line is I think the problem is fixed.

Thank you for the info.

Brad