OBD-II code · Powertrain (generic)
P0840 Transmission Fluid Pressure Sensor/Switch A Circuit Range/Performance
The transmission fluid pressure sensor A reading is implausible compared to commanded line pressure. The TCM detects sensor drift or hydraulic leakage.
Is it safe to drive with P0840?
Usually safe for short trips, but don’t ignore it: the underlying fault can get more expensive over time.
Common causes
- Most likelyPressure sensor drift
- PossibleInternal hydraulic leak
- Less likelySensor element aged beyond calibration window
Symptoms
- Check engine or transmission warning light on
- Harsh, delayed, or missing shifts
- Possible limp mode (locked in one gear)
- Slipping or shuddering during gear changes
Repair at a glance
- Difficulty
- Hard
- DIY friendly
- Best left to a mechanic
- Typical labour
- 2–8 h
- Emissions test
- Usually unaffected
- Parts involved
- Transmission Fluid Pressure Sensor, Valve Body, Transmission Pump
Related codes
- P083BTransmission Fluid Pressure Sensor/Switch G Circuit Range/Performance
- P0841Transmission Fluid Pressure Sensor/Switch A Circuit Range/Performance
- P0846Transmission Fluid Pressure Sensor/Switch B Circuit Range/Performance
- P084BTransmission Fluid Pressure Sensor/Switch H Circuit Range/Performance
- P0871Transmission Fluid Pressure Sensor/Switch C Circuit Range/Performance
- P0876Transmission Fluid Pressure Sensor/Switch D Circuit Range/Performance
- P0988Transmission Fluid Pressure Sensor/Switch E Circuit Range/Performance
- P0993Transmission Fluid Pressure Sensor/Switch F Circuit Range/Performance
- P083DTransmission Fluid Pressure Sensor/Switch G Circuit High
- P083ETransmission Fluid Pressure Sensor/Switch G Circuit Intermittent
- P083FClutch Pedal Switch A/B Correlation
- P0842Transmission Fluid Pressure Sensor/Switch A Circuit Low
- P0843Transmission Fluid Pressure Sensor/Switch A Circuit High
Code data: OBDex open dataset (CC0). Labour times are typical ranges, not a quote.