Fuel Pump "A" Control Circuit High
P0629 indicates the fuel pump control circuit is receiving excessive voltage, preventing proper fuel delivery to the engine. This electrical fault in the fuel pump circuit can cause immediate starting issues, engine stalling, or fuel system shutdown.
What You Might Notice
- Check engine light illuminated
- Engine won't start or fails to crank
- Engine misfire and stalling while driving
- Engine starts then dies shortly after
- Reduced fuel economy or fuel starvation
Most Common Causes
- 1
Fuel pump relay failure
A failed or stuck fuel pump relay can send continuous high voltage to the fuel pump circuit. This causes the overvoltage condition detected by the engine control module.
- 2
Wiring harness short to power
Damaged or shorted fuel pump wiring that contacts positive voltage will cause the circuit voltage to remain abnormally high. Inspect wiring for cuts, abrasions, or improper routing near power sources.
- 3
Engine control module (ECM) malfunction
A faulty ECM may incorrectly regulate the fuel pump control signal, sending excessive voltage output. The ECM fuel pump driver circuit may be failing internally.
- 4
Ground connection failure
A loose or corroded ground connection in the fuel pump circuit prevents proper voltage regulation. Poor grounding causes voltage to remain elevated throughout the circuit.
How to Diagnose It
- 1
Check Fuel pump relay failure — A failed or stuck fuel pump relay can send continuous high voltage to the fuel pump circuit. This causes the overvoltage condition detected by the engine control module.
- 2
Check Wiring harness short to power — Damaged or shorted fuel pump wiring that contacts positive voltage will cause the circuit voltage to remain abnormally high. Inspect wiring for cuts, abrasions, or improper routing near power sources.
- 3
Check Engine control module (ECM) malfunction — A faulty ECM may incorrectly regulate the fuel pump control signal, sending excessive voltage output. The ECM fuel pump driver circuit may be failing internally.
- 4
Check Ground connection failure — A loose or corroded ground connection in the fuel pump circuit prevents proper voltage regulation. Poor grounding causes voltage to remain elevated throughout the circuit.
How to Fix It
- 1
Test and replace fuel pump relay
Use a multimeter to test the fuel pump relay for proper switching behavior. If resistance or voltage readings are out of specification, replace the relay with an OEM or equivalent unit.
- 2
Inspect and repair wiring harness
Trace the fuel pump control circuit wiring from the relay to the pump connector for damage, cuts, or shorts to power. Repair any damaged sections and ensure proper routing away from heat sources.
- 3
Check fuel pump ground connections
Locate all ground points in the fuel pump circuit and clean any corrosion or oxidation from connectors. Tighten all ground terminals to ensure solid electrical contact and proper voltage regulation.
- 4
Test or replace engine control module
If wiring and relay test normal, the ECM fuel pump driver circuit may be faulty. Have the ECM scanned with advanced diagnostics or replaced if the circuit is determined defective.
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