Every time your transmission changes gears, a little plunger mechanism known as a solenoid, directs pressurized transmission fluid down the right channel to move the gears and clutches. If the ECU detects an unusually high-voltage signal along this shift solenoid B control circuit, a P0977 DTC will be saved.
How Serious is the Code?
If the computer is not able to control a shift solenoid, then the transmission will not function properly. The transmission problems related to a P0977 diagnostic trouble code may start out as barely noticeable, but they will continue to get worse. Eventually leading to a nonfunctioning transmission.
Symptoms of a P0977 include:
- Hard gear changes
- Transmission may not shift into gear
- Dirty transmission fluid/filter
- Low on transmission fluid
- Damaged wiring
- Corroded/broken connectors
- The shift solenoid has broken
How to Diagnose the Code?
The condition and level of transmission fluid is the first thing that should be checked when trying to diagnose a P0977 OBDII trouble code. If it’s clean and at the proper level, the wiring and connectors along the transmission wiring harness should be checked for signs of damaged wiring, and/or corroded/broken connectors. If everything is checked out of this point, then the shift solenoid itself will need to be tested.
What Repairs Will Fix P0977?
- Service the transmission
- Replace or repair damage wiring/connectors
- Replace shift solenoid
- P0975 – Shift Solenoid “B” Control Circuit Range/Performance
- P0976 – Shift Solenoid “B” Control Circuit Low