P0946Generic code

P0946 Code: Hydraulic Pump Relay Circuit Range/Performance

The P0946 code means the hydraulic pump relay responds electrically, but the result is not what the computer expects. It can lead to a loss of hydraulic pressure. The fault is often mechanical or hydraulic, so a multimeter alone will not find it.

Severity
High
Can I keep driving?
Yes, but with caution
Estimated cost
$100 to $1,200
Difficulty
Medium
System
Transmission
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

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What the P0946 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. In hydraulic systems, an electric pump keeps up the accumulator pressure that operates the clutch and the shifts, and the computer turns it on through a relay.

The computer monitors the control circuit from its own driver transistor. The P0946 code means the component answers electrically, but the outcome is not the one expected. Before you change the component, check the fuse, the relay, the connector and the wiring, because those are the usual culprits.

If the pump does not run, the system loses pressure and the gearbox stops shifting. If the relay sticks closed, the pump runs nonstop and overheats. After any repair on these parts, the gearbox learning procedures (clutch touch point, selection positions and engagement positions) have to be run with a scan tool. Without them the transmission will not work properly.

This kind of fault usually does not show up with a multimeter, because everything looks fine electrically. You have to compare what the part reports with reality: use a gauge, a thermometer or a tachometer, or command the component with the scan tool and see whether the physical result matches the order.

P0946 code symptoms

  • Check engine light or another warning light on.
  • Loss of hydraulic pressure.
  • The gearbox will not engage gears or stays in neutral.
  • Transmission or engine light on.
  • Beep or warning message on the dash.

Likely causes of the P0946 code

  1. Worn or leaking actuator. The most common cause.
  2. Gearbox mechanism that is stiff or has play. Forks, synchronizers or linkage.
  3. Learning procedures not done after a repair.
  4. Low or degraded hydraulic fluid in hydraulic systems.

How to diagnose the P0946 code step by step

  1. Command the component with the scan tool and see whether the physical result follows the order.
  2. Check the fuse and the relay. Measure voltage on both sides of the fuse and swap the relay with an identical one.
  3. Measure the supply at the connector. You should see battery voltage with the key on, or when the component is commanded.
  4. Measure the component resistance and compare it with the manual, then check the insulation to ground.
  5. Check the control wire for continuity to the computer and for shorts.
  6. Command the actuator with the scan tool and see whether it moves.
  7. Run the gearbox learning procedures after any repair.
  8. Check the hydraulic fluid level and look for leaks.

How to fix the P0946 code

  • Repair the connector, the wiring or the supply.
  • Replace the hydraulic pump relay if it does not respond when it has the right supply and command.
  • Clear the P0946 code and verify the repair.

Technical reference data

  • Electric actuator (DC motor) or hydraulic solenoid valve controlled by PWM.
  • Reference values only: check the manufacturer data for your vehicle.

Brand-specific notes

The makes below are where this family of codes is seen most. In many hydraulic systems the actuator fluid is a specific one, and the reservoir should be checked regularly.

P0946 on Opel

Very common on the Opel Easytronic.

P0946 on Fiat

Very common on the Fiat Dualogic.

P0946 on Toyota

Very common on the Toyota MMT.

P0946 on Smart

Very common on Smart cars with this style of transmission.

P0946 on BMW

Very common on the BMW SMG.

Frequently asked questions about P0946

Can I drive with a P0946 code?
With caution, and only as far as a shop. The gearbox can lose its gears at any moment.
What does the hydraulic pump relay 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. In hydraulic systems, an electric pump keeps up the accumulator pressure that operates the clutch and the shifts, and the computer switches it on through a relay.
Does the part always have to be replaced?
No. Check the fuses, relays, connectors and wiring first, since they cause most of these faults.
How much does it cost to fix P0946?
As a rough guide, between $100 and $1,200. The range is wide because the fault may be a leaking actuator or a simple learning procedure.
What does the P0946 code mean?
It means the pump relay circuit works electrically but the result does not match what the computer expects. That points to a mechanical or hydraulic problem behind the relay.
Will a P0946 code clear itself?
Only if the condition behind it stops. A worn actuator or low fluid will keep setting the code until it is repaired.

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