94 F350 7.3 IDI turbo E4od 2wd
I get a code 29 "insufficient input from PSOM ". This happens about once a day. The transmission goes into fail mode until I shutoff the truck and re-start it. This happens when I am accelerating or just cruising along on the interstate. I have changed the RABS sensor in the rear end. This year truck uses that sensor for speed. The speedometer reads correctly and does not bounce. I have also replaced the RPM sensor and FILP sensor.
What could be causing this?

 

Pulled this off a forum a few days ago..... might want to try it.

This is real interesting to me because I just went through about a month of trying to figure out my similar symtoms.

Mine would begin after about 10 to 20 minutes of driving local but as I drove it would reset itself and work properly.

I replaced the fipl and the manual lever position sensor. Had the codes pulled but did not have any saved codes. Sometimes would run well and other times not.

Finally on a 300 mile trip it got much worse and I noticed it would begin after a bump in the road. It would still reset itself and go but returned almost imediately. I was trying to do a milage test and I reached up and hit the select button on the speedo. At the same instant the tranny went to safe mode. I hit the reset button and lo and behold it reset the tranny. Hit the select again and same thing. So I could go in and out just by hitting the button.

I called the Ford dealer where I knew I could get good advice and ran it by the shop foreman. He was amazed by the situation and said so. suggested the speedo module was bad and guessed it would be 4 to 5 hundred to get the part. But I would have to bring the truck in and have the milage recorded and order a new one. He also said that the signal fron the vss comes to the speedo first and then is sent to the computor. That would explain the symptoms. I never got any speedometer or rpm glitches so figured my vss was ok.

So I decided to take it out and look it over. Was not hard to get out maybe 45 minutes for the first time thru. Got it on the bench and looked it over but could not find any thing that looked out of place. Put it all back together and it has run perfectly ever since. I figure it must have been a bad connection at the plug and doing what I did fixed it. But the plug did not look like it was loose. I have since put close to a thousand miles on it without a problem.

Wow what a relief. The funny thing is I could have ordered the part and put it in and it would have worked. They would have said "see, that was the problem". One other thing was it would malfunction by just hitting the dash above the speedo.

So before you spend anymore time on the truck you might want to try this.

 

Further to what has been posted by PLC7.3, a lot of times a peice of electronic equipment that has a plug on it never gets disturbed, other than by the normal vibration on vehicle operation. This does cause a certain amount of isolated wear on the contact points over a period of time that eventually shows up as "dirty" connections due to oxidization of the metals the connectors are made of. I see this quite often on small aircraft, they usually have more high frequency vibration issues than trucks, but the same principal applies.
When this occurs just unplugging the component and reconnecting it several times will "clean" the connection and return the item to satisfactory operation. What I try to do is disconnect and clean any connections you can get to with a pencil eraser, give it a rinse with contact cleaner, the re-assemble the connector with a good silicone electric grease. This will "almost" permantly fix those type of connector problems. FWIW

 

Thanks, I will try that. I noticed today that it (code 29) happens mostly when I hit a bump in the road. The reset and select buttons don't trigger or clear it.

One other thing I am going to check on, the ground wire for the computer is on the left front fender. That fender has been replaced by the past owner. Wonder if a poor computer ground could be a problem too ?

 

1 Pulled the gauge cluster.
2 Re-connected it.
3 Pulled large plug behind left front fender going to the EEC-IV PCM
4 Re-connected it.

250 miles of bumpy roads so far no problems. Knock on wood. I think the connectors needed to be re-seated. Thanks for the advice.

 

500 miles later got the code 29 while cruise control was on. This is the first time code 29 has happened with the cruise on. I disconected the cruise control box because the signal wire that goes from the PSOM to the PCM also goes to the cruise control.

Have driven 400 miles with the cruise control disconnected and so far no code 29.

 

I have a 1993, speedometer appeared to work just fine, but after sitting this last winter it always wanted to slam into gear and the OD light on the shifter would blink. Pulled codes and found Code 29.

Pulled the instrument cluster, cleaned the connections on the back, plugged it back in and now its shifting correctly again, hooray!