P0603 Ford -

Question

I have a code P0603 accompanied by a code p0781 on my 2001 F350 4x4 Lariat(63k miles).
I get no 1-2 shift unless I accellerate to 20mph or above and then let off on the accellerator.
After it does shift all other functions are normal. I sometimes do heavy towing and have changed the transmission oil about every 12k to 15k miles. I have just changed the oil and filter and found no evidence of mechanical failure in the pan, just the usual small amount of sludge from the clutch plates(about 1/2 tbs). The truck has done this several times in the past, but has always returned to normal after achieving the 1-2 shift as explained earlier. Now it will not. I suspect the solenoid pack or speed sensor, but lack the diagnostic tools to check any further. Any suggestions you may have would be greatly appreciated for further diagnosis before I start throwing parts at it.

Answer 1

P0603 Internal control module KAM error

P0781 1-2 shift error

For the KAM error check the fuse in the engine fuse box listed  as number 15 which is a 5 amp fuse, you could of also gotten this code by disconnecting the battery,As for P0781 this can be from SSA (shift solenoid A) or  SSB (shift solenoid B),or even the wrong gear selecting from the gear selector,When you cahnge transmission filter and fluid, go one step further and change out the Shift solenoid A, B. By the way you are changine fluid too soon.