Diagnostic trouble code P0629 is a generic powertrain fault code that applies to all OBD-II equipped vehicles. It indicates that the powertrain control module has detected a high voltage condition in the fuel pump “A” control circuit.
Exact vehicle application must be verified before diagnosis. The code identifies an electrical fault in the control circuit, but further testing is required to identify the root cause.
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Key Takeaways
- P0629 is a generic OBD-II code indicating a high voltage condition in the fuel pump “A” control circuit.
- Possible causes include damaged wiring, poor electrical connections, a failed fuel pump relay, or a faulty control module.
- Symptoms often include an illuminated Check Engine Light, extended cranking, engine stalling, or a no-start condition.
- Diagnosis requires inspecting the control circuit wiring and testing the fuel pump relay and module outputs.
- Repairs involve fixing damaged wiring or replacing the confirmed failed relay or control module components.
P0629 Code Description and Implications
P0629 is a generic OBD-II diagnostic trouble code. It indicates that the powertrain control module (PCM) or a dedicated fuel pump control module has detected a voltage in the fuel pump “A” control circuit that is higher than the expected operating range.
The fuel pump control circuit manages the electrical power supplied to the fuel pump. A circuit high condition means the module is seeing voltage where it should not, often indicating a short to power or an open ground in the control wiring.
This electrical fault can prevent the fuel pump from receiving the correct power signals, potentially disrupting fuel delivery to the engine. This trouble code requires electrical diagnosis to identify the exact point of failure.
Common Causes of the P0629 Code
Possible causes for a circuit high condition include damaged, chafed, or melted wiring in the fuel pump control circuit that is shorting to a voltage source.
Corroded, loose, or pushed-back pins in the electrical connectors at the fuel pump, relay, or control module can also disrupt the circuit.
A failed fuel pump relay that is internally shorted, or a faulty fuel pump control module or PCM, may also trigger this code.
Symptoms Associated With P0629
The most immediate symptom is an illuminated Check Engine Light. Depending on how the control module responds to the fault, the fuel pump may not activate.
This can result in an extended cranking time before the engine starts, or a complete no-start condition if the fuel pump remains entirely disabled.
If the fuel pump operates erratically due to the electrical fault, the engine may experience stalling, hesitation, or severe misfires under load.
Diagnosing the P0629 Trouble Code
Diagnosis begins by verifying the exact wiring diagram for the specific vehicle to identify the fuel pump “A” control circuit path, relays, and module pins.
Technicians inspect the wiring harness and connectors for visible damage, corrosion, or chafing against sharp metal edges or hot exhaust components.
Using a digital multimeter, they test the control circuit for continuity and check for a short to voltage. The fuel pump relay is also tested or swapped with a known good identical relay.
If the wiring and relay test correctly, the diagnostic procedure may direct testing the control module outputs or evaluating the module itself for internal faults.
Repairing the P0629 Issue
If wiring damage or a short to power is found, the affected harness section must be repaired, soldered, and properly insulated.
If the fuel pump relay fails testing, the confirmed failed relay must be replaced with a component meeting the correct vehicle specification.
If all external circuits and the relay test correctly, follow the manufacturer diagnostic procedure to evaluate or replace the fuel pump control module or PCM.
Cost Considerations for P0629 Repairs
Cost depends on diagnostic time, component accessibility, required parts, programming requirements, and labor.
Repairing wiring or replacing a standard relay involves minimal parts cost and standard labor times. Replacing and programming a dedicated fuel pump control module or PCM requires specialized equipment and additional labor.
Prevention Strategies for Future Occurrences
Inspecting exposed engine and chassis wiring harnesses for chafing, heat damage, or rodent intrusion can help prevent intermittent shorts or open circuits.
Keeping electrical connectors clean and ensuring protective seals are intact may reduce moisture intrusion and terminal corrosion in the fuel pump circuit.
Troubleshooting Tips and Best Practices
Never assume the fuel pump itself has failed just because a control circuit code is present. P0629 specifically identifies an electrical fault in the control wiring or relay, not a mechanical pump failure.
Do not ignore related codes. A fuel pump control circuit fault may appear alongside fuel pressure sensor codes or other fuel delivery network codes.
Check for technical service bulletins related to updated wiring harness routing, revised relays, or control module software updates for your specific model year and configuration.
More OBD-II Codes
| P0628 | P0633 | P0625 | P0600 |
| P0627 | P0638 | P0622 | P0601 |
| P0606 | P0641 | P0621 | P0602 |
| P0605 | P0643 | P0620 | P0607 |
| P0604 | P0645 | P0615 | P0651 |
| P0603 | P0650 | P0652 | P0654 |
Frequently Asked Questions
Is P0629 a generic or manufacturer-specific code?
Yes. P0629 is a generic OBD-II code, meaning its definition as a fuel pump “A” control circuit high fault is standardized across all vehicle makes and models.
Can I drive my car with a P0629 code?
It depends on the severity. If the fuel pump is disabled and the engine stalls or will not start, the vehicle is undrivable and requires immediate repair.
Will disconnecting the battery clear the P0629 code?
Disconnecting the battery may temporarily clear the code, but it does not repair the underlying electrical short or component failure. It also resets readiness monitors.
Can a bad fuel pump cause a P0629 code?
Not directly. P0629 specifically indicates an electrical fault in the control circuit, such as a short to power. A mechanically failed pump typically triggers fuel pressure or performance codes.
Does P0629 always mean the PCM is bad?
No. While a failed PCM or fuel pump control module is a possible cause, the code can also be triggered by damaged wiring, poor connections, or a failed relay.
What Should You Do About the P0629 Code?
Confirm the exact wiring diagram and diagnostic procedure for your specific vehicle application. Because P0629 identifies an electrical circuit fault, tracing the control circuit from the module to the fuel pump is mandatory.
Follow the applicable diagnostic steps to test the wiring, connectors, and relay. Once the root cause is confirmed, repair or replace the confirmed failed components and verify that the fuel system operates correctly.
