The P0628 code is a generic OBD-II trouble code indicating a low voltage condition in the Fuel Pump “A” control circuit. This system manages the low-pressure fuel lift pump.
Because this is a generic code, the exact diagnostic procedure varies by vehicle. The code signals a detected electrical fault, but testing is required to identify the root cause before replacing any components.
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Key Takeaways
- P0628 is a generic OBD-II code indicating a circuit low fault in the Fuel Pump “A” control circuit.
- The code signals a low voltage condition detected by the control module, typically indicating a short to ground.
- Possible causes include damaged wiring, a failed fuel pump driver module, an internally shorted fuel pump, or a PCM fault.
- Diagnosis requires inspecting the fuel pump control circuit and measuring resistance before replacing components.
P0628 Code Description and Implications
The P0628 code indicates that the Powertrain Control Module (PCM) or Fuel Pump Control Module (FPCM) has detected a low voltage condition in the Fuel Pump “A” control circuit.
This circuit typically controls the low-pressure fuel lift pump, which supplies fuel from the tank to the high-pressure pump or fuel rail.
A “circuit low” condition means the module sees voltage below the expected threshold, usually indicating a short to ground in the control or feedback circuit.
Common Causes of the P0628 Code
- Damaged, chafed, or shorted wiring in the fuel pump control circuit.
- Corroded, loose, or moisture-intruded connectors at the fuel pump or control module.
- A failed Fuel Pump Driver Module (FPDM) or FPCM.
- An internally shorted low-pressure fuel pump.
- In rare cases, an internal fault within the PCM.
Symptoms Associated With P0628
- Illuminated Check Engine Light.
- Extended cranking or a no-start condition.
- Engine stalling or severe loss of power under load.
- Activation of a fail-safe or limp mode.
Diagnosing the P0628 Trouble Code
Diagnosis begins by verifying the exact fuel system layout for the vehicle. Using a scan tool capable of viewing fuel pressure data and commanding the pump is necessary.
The diagnostic path generally involves:
- Inspecting the wiring harness and connectors at the fuel tank and FPCM for physical damage, road debris impact, or corrosion.
- Testing the control circuits for a short to ground using a multimeter.
- Measuring the internal resistance of the fuel pump and comparing it to the manufacturer’s specification.
Repairing the P0628 Issue
Repairs must follow the confirmed root cause identified during the diagnostic procedure. If wiring damage or a short to ground is found, repairing the harness and securing the connections is necessary.
If the FPCM or FPDM fails electrical tests or shows internal corrosion, replacing the confirmed failed module is required.
If the fuel pump itself is internally shorted, replacing the confirmed failed pump assembly is necessary.
Cost Considerations for P0628 Repairs
Repair costs for a P0628 code vary based on the exact vehicle application, the confirmed root cause, and local labor rates.
If the issue is limited to a wiring repair, costs may be minimal. Replacing an external FPCM involves moderate expenses, while dropping the fuel tank to replace the pump requires significant labor.
Prevention Strategies for Future Occurrences
Because P0628 relates to the fuel pump control circuit, preventing the code depends on the exact failure mechanism.
Inspecting exposed wiring near the fuel tank can help identify developing damage from road debris.
Ensuring FPCM mounting locations are free from excessive moisture or corrosion can help prevent module failure.
Troubleshooting Tips and Best Practices
Do not assume the fuel pump inside the tank has failed just because of a circuit low code. An external module or a chafed wire is often the root cause.
Check for applicable Technical Service Bulletins (TSBs) regarding FPCM corrosion, as some manufacturers have relocated or updated these modules to prevent water intrusion.
More OBD-II Codes
| P0627 | P0629 | P0625 | P0626 |
| P0620 | P0621 | P0622 | P0654 |
| P0657 | P0650 | P0651 | P0652 |
| P0645 | P0600 | P0601 | P0602 |
| P0603 | P0604 | P0605 | P0606 |
| P0607 | P0087 | P0300 | P0420 |
Frequently Asked Questions
Is the P0628 code generic or manufacturer-specific?
Yes. P0628 is a generic OBD-II code used across multiple manufacturers. However, the exact diagnostic procedure and fuel system layout depend on the specific vehicle application.
Can I drive my car with a P0628 code?
Driving is not recommended. A low voltage fault in the fuel pump circuit can cause the engine to stall unexpectedly, fail to start, or lose power under load, creating a safety hazard.
Will clearing the code fix a P0628 fault?
No. Clearing the code will not repair a short to ground, damaged wire, or failed module. Because P0628 is a hard electrical fault, the code will return immediately upon the next monitor cycle.
Can a bad fuel pump relay cause a P0628 code?
Yes. If the fuel pump relay is part of the control circuit and fails internally shorted, it can trigger a circuit low code. However, wiring shorts and module failures are more frequent causes.
Does P0628 always mean the fuel pump is broken?
No. The code indicates a detected circuit low condition. The root cause could be a shorted wire, a corroded connector, or a failed driver module, requiring diagnosis before replacing any component.
What Should You Do About the P0628 Code?
Confirm the exact factory definition and wiring diagram for your specific vehicle application. Because P0628 is a generic code, the pinout for the Fuel Pump “A” control circuit will vary between different platforms.
Follow the applicable manufacturer diagnostic procedure to test the relevant system and components. Once the root cause is confirmed, complete the necessary repairs and verify the fuel system operation before returning the vehicle to service.
