Troubleshooting F-250 Tranny

[dkryan]

My friend is having a problem with the E40D transmission in his 1995 F-250 with the 7.5L engine.

"Issue
Computer is sending OBD1 error code 621; Truck doesn’t move in D selector, can start out in manual 2 or manual 1 and then shift to D; transmission shifts OK above 15-20 mph. Reverse is OK.

Truck Specs:
1995 F250 with 7.5L engine
E40D transmission

What’s been replaced / repaired -

• Trans rebuilt (previous owner – new solenoid pack)
• Transmission wiring harness- original plug had bare wires showing
• Replaced TPS

Troubleshooting -

• Tested resistance of transmission solenoids – all tested w/in spec ranges
• Put 12V across Shift 1 solenoid – solenoid actuates
• Back pinned Shift 1 solenoid ground wire at Transmission wiring harness and jumped to frame ground.
o Transmission shifted perfectly for 1st & 2nd gear – won’t drop Solenoid 1 for 3rd since the solenoid is grounded outside of PCM control
• Tested for continuity on shift 1 solenoid ground from Transmission plug to PCM – tested OK.

Question -

Is there a sensor input to the PCM that might also result in the computer not completing the ground circuit for the shift solenoid that I should also be considering, or does it look like to PCM might be faulty? If so, any way to test the PCM?"

Thanks!

 

[xxch4osxx]

Clinebarger would be the member to answer this question.

 

[Linctex]

Originally Posted By: dkryan

Troubleshooting -
Transmission shifted perfectly for 1st & 2nd gear – won’t drop Solenoid 1 for 3rd since the solenoid is grounded outside of PCM control


Sounds like a wire rubbed through some where.

Are the trans solenoids like the fuel injectors?
The FI's are 12v hot all the time on one side.... the ECM grounds to other side as needed to fire the fuel injector.
If so.... the part I underlined ^^^ is what you need to find (shorted somewhere)

 

[dkryan]

Is the underlined a link?

If so, it’s not working for me.

Thanks.

 

[spasm3]

I would check alternator output. I had a 93 auto saturn that started out in 3rd gear from a stop, a trans shop figured out it was not my transmission, it was my aftermarket alternator putting out 17 volts. I put a quality alternator on it , and the problem went away.

 

[clinebarger]

These trucks are BAD about having Shift Cable & Shift Lever assembly problems, You will think your in the "OD" range when your actually still in Neutral.

On this truck.....I would run a NEW SS1 control wire from the PCM to the Solenoid pack.....INCLUDING the Terminals!!! There used to be terminal pigtails for these from Ford. If this fails to correct the 621 DTC......The PCM is most likely damaged (Driver or Sensing circuit)

 

[dkryan]

Thanks for the response!