P0842: Transmission fluid pressure sensor/switch A: circuit low
The control unit gets too low a voltage from gearbox fluid pressure sensor A. It is almost always wiring, a connector, an earth or the sensor itself.
| Code | P0842 |
|---|---|
| System | Engine and transmission |
| Group | P08xx, Transmission |
| Type | Generic: it means the same on every make |
| Can you keep driving? | With care |
What P0842 means
The gearbox fluid pressure sensor sends the control unit a voltage that varies with pressure. Here that voltage is below the possible range, which points to an electrical problem rather than the actual pressure. What sensor A is depends on the manufacturer.
Most common causes
- Loose or corroded sensor connector
- Signal wire broken or shorted to earth
- Missing sensor power supply
- Faulty pressure sensor or switch itself
- Gearbox control unit fault (uncommon)
Symptoms
- Engine or gearbox warning light on
- Gearbox in limp mode
- Harsh or mistimed shifts
Can you drive with P0842?
With care You can drive carefully, although the gearbox may stay in limp mode. Have it checked soon.
Open the bonnetthe in-depth explanation
How to check it
Inspect the sensor connector for looseness, moisture or green corrosion. If your scanner shows the sensor value live, gently move the wiring with the engine running and see whether the reading jumps.
How to read and clear P0842 with Final OBD
Plug an OBD2 scanner in under the steering wheel, switch the ignition on and open Final OBD. Under Faults you’ll see P0842 with its description and whether it’s confirmed, pending or permanent.
This code is usually stored by the gearbox control unit. If the car reports it over standard OBD, you read it for nothing with FREE; to read it straight from the gearbox control unit, with its description and clearing, you need PRO.
Clearing the code only turns the light off: if the cause is still there, it comes back. Clear it once it’s fixed, and not right before an inspection. It’s all in how to read and clear fault codes and in inspections and OBD.
Similar codes
- P083E The gearbox oil pressure sensor G fails now and then
- P083F Clutch pedal position switches A and B give conflicting signals
- P0840 The gearbox oil pressure sensor A has an electrical fault
- P0841 Transmission fluid pressure sensor/switch A: circuit range or performance
- P0843 Transmission fluid pressure sensor/switch A: circuit high
- P0844 The gearbox oil pressure sensor A fails now and then
- P0845 The gearbox oil pressure sensor B has an electrical fault
- P0846 The gearbox oil pressure sensor B gives readings outside the normal range
- P0868 Transmission fluid pressure low
What does code P0842 mean?
The gearbox fluid pressure sensor sends the control unit a voltage that varies with pressure. Here that voltage is below the possible range, which points to an electrical problem rather than the actual pressure. What sensor A is depends on the manufacturer.
Can you drive with P0842?
You can drive carefully, although the gearbox may stay in limp mode. Have it checked soon.
How do you clear P0842?
With an OBD2 scanner and an app like Final OBD, which clears it for free if it’s stored by the engine control unit. But clearing it only turns the light off: if the cause isn’t fixed, P0842 comes back.
Read it on your car
Final OBD reads and clears engine faults through standard OBD for free, each one explained in plain English. With PRO it also reads the faults of every control unit, each make’s own codes included, and clears them in all of them.
