When dealing with electrical problems, it’s always important to remember that a single fault can create multiple problems in seemingly unrelated systems. But at the same time, it’s also possible to have more than one fault!
This situation started with a friend of mine who owns a body shop. He purchased a 2012 Expedition with a 5.4 liter engine for his wife and five kids that he planned to use as his family school bus.
But he was having a few problems with it, so he brought it to me to check. According to him, the fuel light would flash while the tank was between quarter and half full. At the same time, the odometer would intermittently display dashes across the numbers.
We took the truck for a long drive and, sure enough, it behaved exactly as he described it. So the first thing I did was to scan codes in the OE protocol part of the computer. I came up with two codes:
P0720 — output speed sensor insufficient input
P0722 — output speed sensor no signal
Interesting; where’s the connection between fuel gauge and odometer?
It turned out the speedometer dropped to zero at the same time, which put the truck into failsafe. Cycling the key reset the transmission to normal operation… until the problem occurred again.
I also notice that the A/C blower was shutting off intermittently; it seemed to coincide with the speedometer and odometer problems. Once again I had to wonder about the connection between the problems.
Next I scanned the OBD global side of the computer. As expected, the output speed sensor codes were in memory and history. Since it can be a little difficult to test the speed sensors, I decided to perform a bulletin search and save a little time.
And there it was: Ford TSB 13-4-9, which supersedes TSB 13-2-3. According to Ford, some 2011-2013 Mustangs, and 2012-2013 F-150s, Expeditions, and Navigators equipped with the 6R80 may exhibit this condition.
The transmission will go into failsafe and start in a higher gear until you cycle the ignition. The wrench light will come on and odometer will display dashes while driving. The only symptoms it didn’t mention was the fuel gauge and the blower motor.
The bulletin also mentions that these codes may not be stored in the powertrain control module (PCM), probably because the condition is intermittent, so when the computer looks for the signal again and it’s back, it has no reason to set a code.
If you cycle the key, it clears the codes and restores normal operation and functionality of the transmission.
The bulletin points to a part Ford calls the Transit Transmission Bulkhead Connector; a big name for what’s basically a complex connector that connects the harness to the transmission. The original part number for the connector was AL3Z-7G276-A; it’s been superseded to AL3Z-7G276-B.
Surprisingly enough, while researching this problem, I ran into compliance recall #12C23-S1, regarding the Internal Mode Switch (IMS).
The symptoms for a faulty IMS are no digital display in the dash or transmission won’t engage in any gear or reverse, and the backup lamps or rear video camera may not work. The IMS is part of the Transit Transmission Bulkhead Connector — the very part we replaced. Replacing the connector updated the IMS at the same time.
The one thing the bulletin didn’t explain was why the A/C blower was dropping out. Turns out it was a completely unrelated problem that seemed to coincide with the transmission problem. The dropout in the blower motor turned out to be caused by a bad connection at the A/C fan relay in the fusebox, inside the engine compartment.
So when dealing with a number of issues that seem to coincide with one another, remember it’s possible to simply have two unrelated problems that happen to occur at roughly the same time. Never assume that fixing one will take care of the others; always check that all the symptoms are gone before attempting to deliver the vehicle.