68 RFE Shifting back and forth

[pcarlson]

The last tow Saturday's when I have used the truck I back out of my heated garage and let it idle while I load up stuff for the dump. Then I drive out of the drive for about 1/2 mile to town and when I let off the throttle to slow to the 25 mph (55 to 25) it bucks back and forth something bad like it is downshifting and upshifting back and forth and it has done this is tow/haul and normal mode. Today when it did this I manually shifted it down to 4th and it quit. This is the only two times the truck has ever done this as otherwise it runs just fine. Fluid levels seem fine and the engine runs smooth and I don't want to snap something off with all this bucking back and forth. Any ideas? I have no check engine light on but I haven't checked for any codes.

 

[transe]

Is your foot completely off the throttle when this happens? Does the dash display still show "D" or do you maybe have a flaky ERS switch (on the shift lever) that thinks you're tapping it back and forth? If the ERS switch is the culprit, you should see a gear number (like "3" or "4") displayed in the cluster.

Best bet to diagnose this would be to take it to a dealer, and ask them to:
• Check for transmission fault code(s)
• Drive it with a scan tool hooked up to monitor current gear and target gear. This will let them see whether the TCM is actually commanding it to shift back and forth.
• If TCM is commanding the unusual back-and-forth shifting, they can also monitor the throttle and output speed readings, to see if a flaky sensor reading is causing it.

 

[pcarlson]

Thank you for the reply. If I remember correctly the display shows "D" both times and my foot was completely off the throttle. Both times the engine and transmission were cold and did not repeat the rest of either drives. One day when they get me in for the recalled steering I'll have them investigate the shifting. Maybe it's as simple as a bad sensor. Thanks again.

 

[Larry Willard]

I had the same problem on my '08 as well on occasion. It was reflashed once or twice, but never seemed to help. The '13 with an Aisin has solved all the problems.
Larry

 

[Mountain]

This happened to me on my 02 2500. I read online to clean the battery terminals. It worked for about three weeks and then the problem reoccured. Clean the terminals again and no issues for a few more weeks. It appeared to be some kind of electrical issue on my truck. I ended up trading it a month later so not sure what the final fix was.