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A P0755 fault code indicates that the PCM has detected an electrical circuit fault with internal transmission Shift Solenoid "B".
If the circuit is shorted, you'll loose 1st gear. If the circuit is open, you'll loose 3rd gear. In either event, the O/D light will flash and your CEL will come on.
The list of possibilities include: PCM, vehicle wiring harness, transmission internal harness, or the solenoid itself.
P0775 indicates The PCM doesn't like the results when it commands Pressure Control Solenoid "C" to a specified pressure. Should also cause a loss of 2nd and 5th gears and, as noticed a MIL.
Might be a faulty solenoid body or a wiring/PCM concern. The workshop manual does have a pinpoint diagnostic procedure, however the procedure requires a test device unlikely to be found outside a dealership.
I took it to a Ford dealer who said I would need a new or used tranny. With close to 140,000 miles on it, I did not want to put that much money into it. (Think they said $3300 for the new tranny).
Never even brought it home, traded it in on a 2008.
I would definately screen any repair shop very thoroughly to make sure they are familiar with the servo bore issue in the 5R55 trannys before letting them rebuild it. Check with Northland Transmissions to see if they can recommend a local shop that is familiar with their repair kit. Once the 5R55 is rebuilt with the kit it is a good strong tranny. It's a shame that it has this design flaw.