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P0940 – Hydraulic Oil Temperature Sensor Circuit High Input (OBD2)

P0940 means "Hydraulic Oil Temperature Sensor Circuit High Input". The voltage in the automated manual gearbox hydraulic unit 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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P0940 quick summary

Fault codeP0940
MeaningHydraulic Oil Temperature Sensor Circuit High Input
SystemPowertrain (Engine & Transmission)
VehiclesGeneric OBD2
SeverityHigh
Can I drive?Not recommended. Loss of hydraulic pressure can leave the gearbox unable to shift or disengage the clutch.
Repair cost€50 – €1,500

How the hydraulic unit of an automated manual gearbox works

Hydraulically operated automated manual gearboxes use an electric pump, accumulator and sensors to provide pressure for the clutch and shift actuators; these codes cover that hydraulic unit.

An electric pump builds hydraulic pressure that is stored in an accumulator. The control unit monitors the pressure with a sensor and the oil temperature with a temperature sensor, and switches the pump through a relay.

Codes P0932–P0941 cover the hydraulic pressure and oil temperature sensors; P0942–P0948 the hydraulic pressure unit, its cycling time, loss of pressure and the pump relay.

If the pump has to run too often (short cycling) or pressure is lost, the accumulator, seals or pump are worn, or there is a leak.

On VAG vehicles (VW, Audi, Škoda, Seat, Cupra), VCDS and older VAG testers can show this code as the five-digit VAG code 17324 (P0940). Both numbers mean the same fault.

Symptoms of P0940

  • Pump running often or continuously (audible whine)
  • Slow or no gear changes
  • Gearbox warning messages
  • Hydraulic fluid leak
  • Car does not start or move

Most common causes of P0940 (most likely first)

Mechanic's Pro Tip

If the pump runs every time you open the door or every few minutes, the accumulator has usually lost its charge – a much cheaper part than the whole hydraulic unit.

  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 automated manual gearbox hydraulic unit

  4. 4.Worn accumulator (loses pressure quickly)

  5. 5.Worn hydraulic pump or failed pump relay

  6. 6.Hydraulic fluid leak

  7. 7.Wiring or connector fault

Step-by-step diagnostic guide

  1. 1

    Read codes and pressure

    Read the gearbox codes and watch hydraulic pressure and pump activity in live data.

  2. 2

    Check signal and ground

    With the ignition on and the automated manual gearbox hydraulic unit 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 and leaks

    Check fluid level and look for leaks at the unit and lines.

  4. 4

    Check pump and relay

    Check the pump relay and pump current; listen to how often the pump runs.

  5. 5

    Test the sensors

    Check the pressure and temperature sensor signals.

  6. 6

    Repair and calibrate

    Replace the accumulator, pump or sensor and run the gearbox learning procedure.

Frequently asked questions

Can I keep driving with P0940?

Not recommended. Loss of hydraulic pressure can leave the gearbox unable to shift or disengage the clutch.

How much does it cost to fix P0940?

Typical repair costs are 50 € – 1500 €, 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 automated manual gearbox hydraulic unit. Always confirm the cause with the tests above before buying parts.

Why does the gearbox pump run so often?

Usually the accumulator or a seal is worn, so the pressure drops quickly and the pump must recharge it.

Can the hydraulic unit be repaired?

Often yes – accumulators, pumps and sensors are available separately or through specialist repairers.

What is the difference between P0940 and similar codes?

P0940 belongs to a group of codes for the same component that differ in the type or location of the fault: P0937 – Hydraulic Oil Temperature Sensor Circuit; P0938 – Hydraulic Oil Temperature Sensor Range/Performance; P0939 – Hydraulic Oil Temperature Sensor Circuit Low Input; P0941 – Hydraulic Oil Temperature Sensor Circuit Intermittent; P0942 – Hydraulic Pressure Unit; P0943 – Hydraulic Pressure Unit Cycling Period Too Short. 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.