P0840 and related codes: transmission fluid pressure sensors and switches
A sensor or switch that reports hydraulic pressure inside an automatic gearbox, lettered A to F, has a circuit fault or an implausible or intermittent signal, or the pressure itself is too low or too high (P0867 to P0869).
SeverityHighCarrying on can cause expensive damage, so deal with it now.
Can you keep driving?Only as far as the workshopWhat does P0840 mean?
Pressure sensors and switches tell the gearbox computer whether pressure has really reached a clutch when it asked for a change, and they protect the gearbox when pressure falls. A circuit code means the signal itself cannot be trusted. P0868, low pressure, is more serious: clutches that are not pressed hard enough slip and burn, and low pressure often follows from low fluid, a worn pump or an internal leak.
What causes P0840?
- A low fluid level from a leak at a seal, a cooler line or the pan gasket
- A failed pressure sensor or switch, often mounted on the valve body
- A damaged wire or a connector letting fluid in
- A worn pump or an internal leak that really lowers pressure
- A clogged filter starving the pump
What to check first for P0840
- Check the fluid level first, and look under the car for leaks
- Read the pressure on a scan tool and compare it with what the computer commands
- Have the real pressure measured with a gauge, to tell a false reading from a real one
- Inspect the pressure sensor's connector and wiring at the gearbox
Can you drive with P0840?
Drive only to a workshop, gently. If the code reports low pressure, the gearbox may slip and damage itself quickly; if it slips, the engine speed flares or the car refuses to move, stop and have it towed.
Since May 2018 an engine warning light that stays on is a major defect at the MOT, so the car fails until the fault is fixed.
Codes on this page
33
- P0840Transmission Fluid Pressure Sensor/Switch "A" Circuit
- P0841Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/Performance
- P0842Transmission Fluid Pressure Sensor/Switch "A" Circuit Low
- P0843Transmission Fluid Pressure Sensor/Switch "A" Circuit High
- P0844Transmission Fluid Pressure Sensor/Switch "A" Circuit Intermittent
- P0845Transmission Fluid Pressure Sensor/Switch "B" Circuit
- P0846Transmission Fluid Pressure Sensor/Switch "B" Circuit Range/Performance
- P0847Transmission Fluid Pressure Sensor/Switch "B" Circuit Low
- P0848Transmission Fluid Pressure Sensor/Switch "B" Circuit High
- P0849Transmission Fluid Pressure Sensor/Switch "B" Circuit Intermittent
- P0867Transmission Fluid Pressure
- P0868Transmission Fluid Pressure Low
- P0869Transmission Fluid Pressure High
- P0870Transmission Fluid Pressure Sensor/Switch "C" Circuit
- P0871Transmission Fluid Pressure Sensor/Switch "C" Circuit Range/Performance
- P0872Transmission Fluid Pressure Sensor/Switch "C" Circuit Low
- P0873Transmission Fluid Pressure Sensor/Switch "C" Circuit High
- P0874Transmission Fluid Pressure Sensor/Switch "C" Circuit Intermittent
- P0875Transmission Fluid Pressure Sensor/Switch "D" Circuit
- P0876Transmission Fluid Pressure Sensor/Switch "D" Circuit Range/Performance
- P0877Transmission Fluid Pressure Sensor/Switch "D" Circuit Low
- P0878Transmission Fluid Pressure Sensor/Switch "D" Circuit High
- P0879Transmission Fluid Pressure Sensor/Switch "D" Circuit Intermittent
- P0987Transmission Fluid Pressure Sensor/Switch "E" Circuit
- P0988Transmission Fluid Pressure Sensor/Switch "E" Circuit Range/Performance
- P0989Transmission Fluid Pressure Sensor/Switch "E" Circuit Low
- P0990Transmission Fluid Pressure Sensor/Switch "E" Circuit High
- P0991Transmission Fluid Pressure Sensor/Switch "E" Circuit Intermittent
- P0992Transmission Fluid Pressure Sensor/Switch "F" Circuit
- P0993Transmission Fluid Pressure Sensor/Switch "F" Circuit Range/Performance
- P0994Transmission Fluid Pressure Sensor/Switch "F" Circuit Low
- P0995Transmission Fluid Pressure Sensor/Switch "F" Circuit High
- P0996Transmission Fluid Pressure Sensor/Switch "F" Circuit Intermittent
Related codes
Checked on · Rafael Soares
These are the generic meanings every manufacturer shares. Each brand adds its own detail, so your car's handbook, its service information and a qualified mechanic have the last word. OdoKeep has no connection with any manufacturer, and the app does not read codes from the car.
