Hydraulic Pump Relay Circuit Range/Performance
The P0946 code indicates that the powertrain control module (PCM) has detected an abnormal voltage or resistance in the hydraulic pump relay circuit. This relay controls power to the hydraulic pump, which is often used in transmission or brake systems. The issue may be due to a faulty relay, wiring problems, or a failing pump, leading to intermittent or complete loss of hydraulic pressure.
01. Most Common Causes
- Faulty hydraulic pump relay
- Corroded or damaged wiring/connectors in the relay circuit
- Blown fuse or poor electrical connection
- Defective hydraulic pump drawing excessive current
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission shifting issues or harsh engagement
- Brake pedal feels hard or requires more effort
- Hydraulic pump running continuously or not at all
03. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm the code and check for related codes.
Step 2: Visually inspect the hydraulic pump relay, fuse, and wiring for damage or corrosion.
Step 3: Test the relay coil and switch contacts with a multimeter per manufacturer specs.
Step 4: Check voltage and ground at the relay socket with the ignition on.
Step 5: If relay and wiring are good, test the hydraulic pump motor for proper operation and current draw.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. Driving with a faulty hydraulic pump relay can lead to loss of power steering, transmission failure, or brake assist, creating a safety hazard.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150 for parts and labor, depending on whether the relay, wiring, or pump needs replacement.