Shift solenoids are turned on and off by the vehicle’s computer, when it sends an electrical signal through a coil of wire that is wrapped around a plunger mechanism inside the solenoid. If the ECU detects unusually high-voltage coming through the shift solenoid F control circuit, it will save a P0999 DTC.
How Serious is the Code?
A P0999 diagnostic trouble code can be very serious, even though the symptoms may not be all that bad at first. But they will increase to the point that the vehicle will not be able to be safely driven.
Symptoms of a P0999 include:
- Gear changes are very abrupt
- The transmission refuses to go into a gear
- The transmission fluid is dropped below safe operating levels
- The transmission fluid has become too dirty
- Damaged/broken wires
- Broken/corroded connectors
- The shift solenoid has failed
How to Diagnose the Code?
The process of diagnosing a P0999 OBDII trouble code, should begin with a check of the level and condition of the transmission fluid. If it’s clean and at the proper level, then the wiring and connectors along the transmission wiring harness should be inspected for signs of damage and corrosion. If there are no problems found up to this point, then the solenoid F itself will have to be tested.
What Repairs Will Fix P0999?
- Service the transmission
- Replace or repair damage wiring/connectors
- Replace shift solenoid
- P0997 – Shift Solenoid “F” Control Circuit Range/Performance
- P0998 – Shift Solenoid “F” Control Circuit Low