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P0878 – Transmission Fluid Pressure Sensor/Switch D Circuit High (OBD2)

P0878 means "Transmission Fluid Pressure Sensor/Switch D Circuit High". The voltage in the transmission fluid pressure sensor/switch circuit is above the permitted maximum. For most sensors this points to an open signal or ground wire – the signal "floats" up to the reference voltage – or to a short to voltage.

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P0878 quick summary

Fault codeP0878
MeaningTransmission Fluid Pressure Sensor/Switch D Circuit High
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityHigh
Can I drive?Carefully and only to a workshop. Low hydraulic pressure can cause slipping and damage.
Repair cost€50 – €2,500

How gearbox pressure sensors and switches work

Transmission pressure sensors and switches confirm that hydraulic pressure is present in each circuit; these codes cover their signals, low or high fluid pressure and deteriorated fluid.

Many automatic and dual-clutch gearboxes have pressure switches or sensors (A–F) that report whether pressure has reached a clutch circuit. The control unit uses them to confirm shifts and to detect slipping or hydraulic faults.

Codes P0840–P0849, P0870–P0879 and P0987–P0996 report circuit, range, low, high and intermittent faults; P0867–P0869 report fluid pressure that is too low or too high; P0897 means the control unit has calculated that the fluid has deteriorated.

Low pressure can be caused by low fluid level, a clogged filter, a weak pump or internal leaks; sensor faults by internal harness problems.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 17262 (P0878). Both numbers mean the same fault.

Symptoms of P0878

  • Harsh, slipping or delayed shifts
  • Limp mode
  • Gearbox warning light
  • No drive or delayed engagement
  • Fluid service reminder (deteriorated fluid)

Most common causes of P0878 (most likely first)

Mechanic's Pro Tip

For P0897 (fluid deteriorated), a fluid change alone is not enough on many cars – the fluid ageing counter must also be reset with a scan tool, or the code will return.

  1. 1.Open circuit in the signal or ground wire

    Most likely

    A loose ground connection is a very common cause.

  2. 2.Signal wire shorted to the 5 V reference or battery voltage

  3. 3.Faulty transmission fluid pressure sensor/switch

  4. 4.Low fluid level or clogged filter

  5. 5.Internal harness or connector fault

  6. 6.Weak oil pump or internal leak

  7. 7.Old, degraded fluid

Step-by-step diagnostic guide

  1. 1

    Read codes and pressure values

    Read the transmission codes and pressure values in live data.

  2. 2

    Check signal and ground

    With the ignition on and the transmission fluid pressure sensor/switch plugged in, back-probe the signal and ground wires. A signal stuck at reference or battery voltage points to an open ground/signal wire or a short to voltage.

    Multimeter: Ground wire to battery negative: below about 0.1 V. Signal stuck at about 5 V (or 12 V) = open or short to voltage.

  3. 3

    Check fluid level and condition

    Check fluid using the manufacturer's procedure and temperature.

  4. 4

    Check the sensor circuit

    Measure the sensor supply, ground and signal or switch state.

  5. 5

    Measure line pressure

    Measure real pressure with a gauge where possible.

    Multimeter: Compare with the specification for the gear and engine speed.

  6. 6

    Repair and adapt

    Replace the sensor, filter or fluid, or repair the hydraulic fault, then run adaptations.

Frequently asked questions

Can I keep driving with P0878?

Carefully and only to a workshop. Low hydraulic pressure can cause slipping and damage.

How much does it cost to fix P0878?

Typical repair costs are 50 € – 2500 €, depending on the cause and the vehicle. The most common fixes are: open circuit in the signal or ground wire; signal wire shorted to the 5 V reference or battery voltage; faulty transmission fluid pressure sensor/switch. Always confirm the cause with the tests above before buying parts.

What does 'transmission fluid deteriorated' mean?

The control unit has calculated, from temperature and time, that the fluid is worn out and should be changed.

Can a pressure sensor cause limp mode?

Yes. Without a reliable pressure signal, the gearbox may switch to a safe mode.

What is the difference between P0878 and similar codes?

P0878 belongs to a group of codes for the same component that differ in the type or location of the fault: P0875 – Transmission Fluid Pressure Sensor/Switch D Circuit; P0876 – Transmission Fluid Pressure Sensor/Switch D Circuit Range/Performance; P0877 – Transmission Fluid Pressure Sensor/Switch D Circuit Low; P0879 – Transmission Fluid Pressure Sensor/Switch D Circuit Intermittent; P0897 – Transmission Fluid Deteriorated; P0987 – Transmission Fluid Pressure Sensor/Switch E Circuit. The tests on this page apply to the whole group; the type of fault tells you where to start.

Related fault codes

This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.