The job of a transmission fluid pressure sensor is to inform the ECU how much hydraulic pressure is available to make a shift. If there is an intermittent problem with the TFPS sensor, a P0991 DTC will be triggered.
What Transmission Do I Have?
How Serious is the Code?
Having a P0991 diagnostic trouble code is extremely serious, and can result in a number of transmission problems that include abrupt gear changes and the refusal of the transmission to shift at all.
Symptoms
Symptoms of a P0991 include:
- Gear changes happen abruptly
- Transmission refuses to go into gear
- Limp Mode
Causes
- Low transmission fluid
- Dirty transmission fluid
- Broken/corroded connectors
- Damaged wiring
- The transmission line pressure sensor/transmission fluid pressure sensor has gone bad
- Valve body issues
How to Diagnose the Code?
When starting to diagnose the cause of a P0991 OBDII trouble code, it’s important to check the level and condition of the transmission fluid. If it looks clean and bright, then the wiring and connectors along the transmission wiring harness will need to be checked for signs of damage and corrosion. If everything looks good there, then the transmission line pressure sensor will need to be tested. If it works properly, then further mechanical diagnosis will be needed.
What Transmission Do I Have?
What Repairs Will Fix P0991?
- Add or change transmission fluid and filter
- Repair or replace damaged wiring and connectors
- Replace transmission fluid pressure sensor/switch
- Repair or install remanufactured valve body
Related Codes
- P0987 – Transmission Fluid Pressure Sensor/Switch “E” Circuit
- P0988 – Transmission Fluid Pressure Sensor/Switch “E” Circuit Range/Performance
- P0989 – Transmission Fluid Pressure Sensor/Switch “E” Circuit Low
- P0990 – Transmission Fluid Pressure Sensor/Switch “E” Circuit High.
