The transmission fluid pressure sensor is designed to detect the hydraulic pressure levels inside the gearbox, then translate that into an electrical signal that the ECU then interprets, so it can decide on the best shift strategy. If there is an unusually high-voltage signal coming from the transmission fluid pressure switch E circuit, the ECU will trigger a P0990 DTC.
How Serious is the Code?
The transmission problems caused by a P0990 diagnostic trouble code can range from unusually hard gear changes, to the transmission not being able to engage in particular gear.
Symptoms of a P0990 include:
- Gear changes are unusually harsh
- Transmission unable to engage a gear
- Limp Mode
- 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?
Since not having enough transmission fluid, or having dirty transmission fluid, can affect the transmission line pressure, the process of diagnosing a P0990 OBDII trouble code begin with checking the transmission fluid. If it looks good, then the wiring and connectors along the transmission wiring harness will need to be checked for signs of damaged/frayed wires and/or broken/corroded connectors. If that all looks good, then the transmission line pressure switch will need to be examined. If it checks out, then suspect an internal mechanical problem.
What Repairs Will Fix P0990?
- 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
- 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
- P0991 – Transmission Fluid Pressure Sensor/Switch “E” Circuit Intermittent