P0940Generic code

P0940 Code: Hydraulic Oil Temperature Sensor Circuit High

The P0940 code means the signal from the hydraulic oil temperature sensor is above its maximum value. It usually points to an open circuit or a broken ground. Shifts can turn slower or harsher, mostly on a cold start.

Severity
Medium
Can I keep driving?
Yes, but with caution
Estimated cost
$40 to $400
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0940 code means

Automated manual transmissions (Opel Easytronic, Fiat Dualogic, Toyota MMT, BMW SMG, Ford Durashift, Volkswagen ASG) and many dual-clutch gearboxes use electric or hydraulic actuators to release the clutch, pick the gear plane (selection) and engage the gear (engagement). The transmission computer watches every actuator through position sensors. The temperature of the hydraulic fluid changes how thick it is, and the computer uses that temperature to adjust the timing of each actuation.

The sensor changes its resistance with temperature and the computer reads the resulting voltage. The P0940 code is a high signal, and it usually comes from an open circuit or an interrupted ground.

Without this signal the computer uses a fixed value, and shifts can come out slower or harsher when the car is cold.

To confirm it, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm. An infinite reading means the wire is open. If the wiring is good, measure the component itself: infinite resistance confirms it is open inside.

P0940 code symptoms

  • Check engine light on.
  • Shifts that are slower or harsher than normal.

Likely causes of the P0940 code

  1. Loose or broken connector. The most common cause.
  2. Signal or ground wire cut. The signal climbs up to the reference voltage.
  3. Sensor open inside. Infinite resistance.
  4. Short to 5 V or 12 V from rubbing against another wire in the harness.

How to diagnose the P0940 code step by step

  1. Read the sensor value on the scan tool and compare it with the real fluid temperature.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check the supply and ground with the key on: the reference should be correct and the ground should drop less than 0.1 volt.
  4. Measure the signal with the connector plugged in and see whether it changes with the condition.
  5. Do the wiggle test on the harness with the scan tool in graph mode.
  6. Check continuity of each wire to the computer, which should be under 1 ohm.

How to fix the P0940 code

  • Repair the connector or the wiring.
  • Replace the sensor if the tests confirm it is open inside.
  • Correct the real condition if there is one.
  • Clear the P0940 code and verify with a road test.

Technical reference data

  • NTC thermistor: its resistance drops as the fluid gets hotter.
  • Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

These are the makes where this family of codes turns up most. On many hydraulic systems the actuator fluid is a specific one, so check the reservoir on a schedule.

P0940 on Opel

Very common on the Opel Easytronic.

P0940 on Fiat

Very common on the Fiat Dualogic.

P0940 on Toyota

Very common on the Toyota MMT.

P0940 on Smart

Very common on Smart cars with this style of gearbox.

P0940 on BMW

Very common on the BMW SMG.

Frequently asked questions about P0940

Can I drive with a P0940 code?
Yes, with caution. Shifts may be slower or harsher, but the car normally keeps running.
Does the sensor have to be replaced?
Only if the tests confirm it. The connector and the wiring fail just as often as the sensor does.
What does the hydraulic oil temperature sensor do?
Automated manual transmissions (Opel Easytronic, Fiat Dualogic, Toyota MMT, BMW SMG, Ford Durashift, Volkswagen ASG) and many dual-clutch gearboxes use electric or hydraulic actuators to release the clutch, pick the gear plane (selection) and engage the gear (engagement). The transmission computer watches each actuator with position sensors. The temperature of the hydraulic fluid changes its thickness, and the computer uses it to adjust the timing of each actuation.
How much does it cost to fix P0940?
As a rough guide, between $40 and $400. A reseated connector or a repaired wire costs little, while a new sensor with labor costs more.
What does the P0940 code mean?
It means the oil temperature signal is higher than the maximum the computer allows. That usually points to an open circuit or a ground that is interrupted.
Will a P0940 code clear itself?
Not if the connector is broken or the wire is cut, because the fault is still there. If it was a one-time glitch, the light may go out after several drive cycles.

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