Shift Pointers
- Author: Pete Luban, ATSG Technical Supervisor
What Makes an E4OD Downshift During a Left Turn?
If I remember correctly, a few articles ago I began by saying something like “nothing weird this time.” Well, that doesn’t last too long these days. It’s time for weird again.
A customer brought in this 1997 Ford F-250 (yep, it’s a Ford again) Power Stroke with an E4OD with a complaint of downshifting whenever he made a left turn. Right turns were fine; no problem (I told you it was weird). As the technician was driving the truck to verify the complaint, he noticed that when the signal switch was turned on to signal for a left hand turn, the truck would fall out of lockup. This was verified by the customer as the complaint of sudden downshifting.
The technician also noticed that when cruise control was engaged, while signaling to change lanes to the left, cruise control would also be canceled along with lockup. In situations such as this you might start thinking VSS, MLPS or possibly a temperature-related problem could be causing all of this – NOT!
When the technician returned to the shop, a scan for codes resulted in zip, nada, nothing – no codes stored!
Another thing he noticed was that one of the rear turn-signal bulbs was burned out, but replacing it did not cure any of the complaints. Another odd occurrence that he noticed was that when the ignition key was turned off, the left signal lamp was still lit.
Frankly, if I were handling this situation, and these sensors checked good, I might start looking for some trailer-wiring problems that I recall Ford was experiencing in relation to wire-harness routing – but, of course, that’s not the fix here, either.
Believe it or not, the cause of all of this was a faulty signal switch, or what Ford calls a multi-function switch. Replacing the switch solved all the complaints.
If you look at the exterior-lighting wire diagram in Figure 1, you will notice that the turn signals, brake switch and cruise control are all tied together. What I think happened here is that the faulty signal switch caused a voltage drop across the brake switch, which caused the PCM to think the brake switch was applied, causing a cancellation of lockup and cruise control. I believe this is so because we have all been victims of lockup problems caused by burned-out stoplight bulbs or TCC cycling because of the four-way flasher.
To add to the problem, the technician had to be able to tell the difference between the normal action of stepping on the brake to slow for a turn, which would cancel lockup and cruise control, and the actual turning on of the signal switch causing the same actions.
This just adds another “I don’t do that kind of work” item to the list of things we are now doing because it directly affects the way the transmission operates.
Special thanks to Donald Holliday of Covington Automotive in Covington, La., for taking the time to share his experience with me. Congratulations, Donald, for a job well done.
