Hydraulic Pump Relay Circuit Range/Performance
Diagnostic trouble code P0946 indicates that the powertrain control module (PCM) or transmission control module (TCM) has detected an out-of-range or unexpected voltage signal from the hydraulic pump relay circuit. This means the hydraulic pump, which provides necessary fluid pressure for automated manual or dual-clutch transmissions, is not operating within the expected performance parameters.
This code is considered high severity because a failing hydraulic pump circuit can lead to a complete loss of transmission fluid pressure. This may result in the vehicle being unable to shift gears or move, potentially stranding the driver.
Common symptoms
- Illuminated Check Engine Light or Transmission Warning Light
- Transmission slipping or failing to engage gears
- Harsh or erratic shifting
- Vehicle enters limp mode (reduced power)
- Inability to move the vehicle (no drive or reverse)
Likely causes
- Faulty hydraulic pump relay
- Blown fuse or fusible link in the hydraulic pump circuit
- Corroded, damaged, or loose wiring and connectors in the relay circuit
- Failing transmission hydraulic pump
- Low transmission hydraulic fluid level
- Faulty Transmission Control Module (TCM) or PCM (rare)
What to check before replacing parts
Check the transmission hydraulic fluid level and condition.
Look for: Fluid that is significantly low, burnt, or heavily contaminated indicates a leak or internal transmission issue that could cause the pump to overwork or fail.
Inspect the hydraulic pump relay and related fuses.
Look for: A blown fuse or a relay that fails a bench test (does not click or lacks continuity across the switched pins when energized) indicates a power supply issue to the pump.
Visually inspect the wiring harness and connectors for the hydraulic pump and relay.
Look for: Look for frayed wires, melted insulation, or corroded connector pins that would cause high resistance or an open circuit.
Test the voltage and ground at the hydraulic pump relay socket.
Look for: With the key on, the control side should have battery voltage and a good ground signal from the TCM. The load side should have constant battery voltage. Missing voltage or ground indicates a wiring or module issue.
Apply direct power and ground to the hydraulic pump (if accessible) to test its operation.
Look for: If the pump does not run, sounds excessively noisy, or draws excessive amperage when directly powered, the pump itself has failed internally.
This page explains the generic P0946 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
Gear guide: Best OBD2 ScannersRead this code yourself next time — from $20 Bluetooth dongles to bidirectional scan tools.Rather have a pro handle it? Find a vetted local mechanic.