Our subject today is a 2011 Ford F-250 Super Duty 4×4 with a 6.7L diesel and automatic transmission, with 100,000 miles and about 2,900 engine hours (each hour is roughly the equivalent of 25 miles, so basically this engine has 172,500 miles on it).

The complaint here was that the truck wouldn’t start unless your foot was on the brake pedal. This would be normal on a vehicle with an ignition system like the one pictured above (push button starter), but is not normal on an ignition system that uses a traditional key, like this F-250.

Part two of the complaint was a check engine light, a wrench light, and that the transmission would slam into every gear.

I know what you’re thinking. “Transmission is shot.” Right?

The technician scanned the stored trouble codes, and came up with these:

  1. P0706 Transmission Range Sensor “A” Circuit Range/Performance
  2. P0707 Transmission Range Sensor “A” Circuit Low
  3. P1702 Transmission Range Sensor Circuit Intermittent
  4. P1783 Transmission Over temperature Condition
  5. P1921 Transmission Range Signal

The Transmission Control Module (TCM) was the culprit in this case. This is basically the computer that controls the transmission’s behavior. Internal failure was causing the TCM to believe that the truck was in drive at all times, and only pressing the brake would disengage it, which is why it wouldn’t start. Ever tried starting a vehicle in any gear besides neutral or park? It’s a safety feature.

The TCM was the cause of all the concerns on this truck. It just needed a replacement TCM with a reprogram and it ran and drove perfect after that.