Hello everyone. I have a 1999 F350 SD 7.3L Auto 4x4. My trans has just started shifting weird. It will shift from first to second to third very fast if I am just starting out slowly. It shifts up into the higher gears before I am hardly getting going. Then it will shift back and forth from 3rd and 4th about a dozen times. After that the OD light will start flashing and it will stay in 3rd.

Also, the speedo doesn't always work correctly. Sometimes as I'm heading down the road at 65 it will drop down to 0. Sometimes it will drop down to 55. Sometimes it bounces around from 45 to 55. I have replaced the VSS on the rearend with a new one from the auto parts store. If I have the cruise control set when the speedo starts to drop, the truck will start to speed up.

I have a Diablo Programmer that came with the truck when I purchased it. When I used it to check the codes I got the following:

P0733 Gear 3 Incorrect
P0603 Powertrain Control Module
P1728 Transmission slip
P0732 Gear 2 Incorrect
P0715 Turbine Input Shaft

I was also watching some of the live data while I was driving. I'm really not sure what I should be looking at but one thing looked out of place. The TPS reading was 0.0v.

From what I understand so far, 0733 and 0722 could be from the engine rpm being higher than expected. 0603 could be related to my speedo problem. 1728 could be because the torque converter isn't locking. 0715 is probably the ISS sensor on the front/top of the trans.

I am looking for suggestions on what to replace first. I'm thinking of 3 different things. TPS, ISS, and the gauge cluster.

Thanks for any help or suggestions on other things I can check.

 

The first thing to do, is put the truck back to stock and see if this still happens. Some of these off the shelf programers will do some funny thing to the engine and trans.

 

With that speedo not working properly, i would suspect it is your VSS sensor on top of the rearend.. Napa has them (they called is a ABS sensor) P/N 530780.. around $12.

 

These are the steps I would start with.

Make sure TSS (what you call the ISS) connector is clean and reseat. Test drive. If same problem remove the TSS to see if it has wear metals stuck to it. If so clean and re-install and test drive. If the problem is still there swap the TSS with the OSS (they are interchangeabe) and see if you get a code for the OSS. That would tell you the sensor that was the TSS, and now the OSS, is bad.



The P0603 is from having the batts disconnected and loosing power to the PCM. You have to clear the KAM (Keep Alive Memory) to get rid of it.

There are two places to see throttle pedal position. One is for a gasser and the other for the diesel. Can't remember the exact names. One is throttle positon and I believe the other is accelerator position. Sounds like your TPS is working or you wouldn't be able to accelerate.