Hydraulic Pump Relay Circuit/Open
Diagnostic trouble code P0945 indicates that the transmission control module has detected an open circuit or electrical fault in the hydraulic pump relay control circuit. The module sets this code when it cannot detect the expected voltage or continuity required to operate the transmission's hydraulic pump relay.
This code requires immediate attention because a failing hydraulic pump circuit can cause the transmission to lose pressure, resulting in an inability to shift gears or a complete loss of vehicle propulsion.
Common symptoms
- Illuminated Check Engine Light
- Transmission slipping or harsh shifting
- Inability to shift into gear
- Vehicle stuck in limp-home mode
- Delayed transmission engagement
Likely causes
- Faulty hydraulic pump relay
- Blown fuse or fusible link in the transmission circuit
- Damaged, corroded, or loose wiring in the relay control circuit
- Faulty transmission hydraulic pump motor
- Failing Transmission Control Module (TCM) or Powertrain Control Module (PCM)
What to check before replacing parts
Inspect the transmission system fuses and fusible links.
Look for: A blown fuse indicates a short circuit or an overloaded hydraulic pump motor that needs further investigation.
Visually inspect the wiring harness and connectors associated with the hydraulic pump relay.
Look for: Look for frayed wires, corrosion, melted insulation, or loose pins that could cause an open circuit.
Test the hydraulic pump relay using a multimeter or by swapping it with a known good identical relay.
Look for: If the swapped relay restores function or the original relay fails a continuity/resistance test, the relay is defective.
Measure voltage and ground at the hydraulic pump relay socket with the ignition on.
Look for: The presence of battery voltage and a solid ground confirms the circuit up to the relay is intact; absence indicates a wiring or module issue.
Verify the control signal from the TCM/PCM to the relay using a scan tool and multimeter.
Look for: If the module commands the pump on but no voltage change occurs at the relay control pin, the module or the wire from the module may be faulty.
This page explains the generic P0945 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.
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