Hydraulic Pump Relay Circuit Low Voltage
The P0947 code indicates that the powertrain control module (PCM) has detected a low voltage condition in the hydraulic pump relay control circuit. This relay supplies power to the hydraulic pump, which is essential for systems like power steering or transmission control. A low voltage reading suggests a short to ground, open circuit, or faulty relay, potentially causing the pump to operate intermittently or not at all.
1. Symptoms You Will Notice
- Illuminated check engine light
- Loss of power steering assist
- Transmission shifting issues
- Hydraulic pump not operating
- Increased steering effort
2. Most Common Causes
- Faulty hydraulic pump relay (open coil, burned contacts)
- High resistance, corrosion, or loose connection in the relay circuit wiring
- Short to ground in the relay control circuit
- Blown or incorrect amperage fuse in the relay circuit
- Hydraulic pump drawing excessive current (internal short)
- Relay or hydraulic pump connector damaged by moisture/corrosion
- Damaged PCM relay control circuit (less common)
3. Step-by-Step Diagnosis
Step 1: Use a scan tool to confirm P0947 and check for related codes.
Step 2: Inspect the hydraulic pump relay and its wiring for damage, corrosion, or loose connections.
Step 3: Test relay coil resistance and compare to specifications; replace if out of range.
Step 4: Check for voltage at relay control circuit from PCM; if low, repair short or open.
Step 5: If all else passes, test PCM output or reprogram/replace PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended as loss of power steering or transmission function can lead to unsafe driving conditions.
How much does it cost to fix?▼
Typically $50-$150 for relay replacement and wiring repair; PCM replacement can cost $500-$1000.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.