Fuel Pump Control Circuit High Voltage
Code P0629 indicates that the PCM has detected a high voltage condition in the fuel pump control circuit. This typically means the voltage signal from the fuel pump relay or driver module is above the expected range, often due to a short to power, faulty relay, or wiring issue. The fuel pump may run continuously or at full speed, leading to potential overpressure or electrical damage.
1. Most Common Causes
- Short circuit to battery voltage (B+) in the fuel pump control circuit wiring
- Faulty fuel pump control module (FPCM)
- Defective or damaged fuel pump relay
- Corroded, loose, or damaged circuit connections or terminals
- Internal ECM failure (less common)
- Fuel pump with abnormal internal resistance causing high voltage feedback
2. Symptoms You Will Notice
- Engine may run rich or have poor fuel economy
- Fuel pump runs continuously with key on
- Check Engine Light illuminated
- Possible no-start or hard start condition
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Visually inspect fuel pump relay, fuse, and wiring for shorts or damage.
Step 3: Test fuel pump relay operation using a multimeter (check for stuck closed).
Step 4: Measure voltage at fuel pump connector with key on; should be 12V only briefly. If constant, trace short.
Step 5: Check fuel pump driver module (if equipped) for internal short.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
Not recommended. High voltage can cause the fuel pump to run continuously, potentially leading to fuel system overpressure, electrical damage, or fire risk.
How much does it cost to fix?▼
Typically $50-$150 for diagnosis and repair, but can be higher if the fuel pump module or PCM needs replacement.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.