Fuel Pump Secondary Circuit Low
The fuel pump secondary circuit is detecting low voltage, meaning the fuel pump relay or its control circuit isn't providing adequate power to operate the fuel pump. Without proper fuel pump operation, the engine cannot maintain fuel pressure and will stall or fail to start.
What You Might Notice
- Engine will not start or cranks but won't turn over
- Engine starts then immediately stalls
- Engine hesitation or misfiring during acceleration
- Inadequate fuel pressure causing rough idle
- Complete loss of fuel supply to injectors
Most Common Causes
- 1
Defective fuel pump relay
The relay that controls power to the fuel pump has failed internally, preventing it from closing the circuit and delivering voltage to the pump. This is the most common cause of P0231.
- 2
Open circuit in fuel pump wiring harness
Chafed, broken, or corroded wires in the fuel pump supply circuit between the relay and pump create an open circuit, blocking power delivery. Check for pinched or damaged insulation along the fuel line route.
- 3
Blown fuel pump fuse
An internal short in the fuel pump circuit has blown the fuse, cutting power to the relay. The fuse blows as a protective measure when excessive current is detected.
- 4
Loose or corroded connectors
Poor electrical connections at the fuel pump relay socket, fuel pump connector, or ground points create resistance and voltage drop, preventing proper circuit operation.
How to Diagnose It
- 1
Check Defective fuel pump relay — The relay that controls power to the fuel pump has failed internally, preventing it from closing the circuit and delivering voltage to the pump. This is the most common cause of P0231.
- 2
Check Open circuit in fuel pump wiring harness — Chafed, broken, or corroded wires in the fuel pump supply circuit between the relay and pump create an open circuit, blocking power delivery. Check for pinched or damaged insulation along the fuel line route.
- 3
Check Blown fuel pump fuse — An internal short in the fuel pump circuit has blown the fuse, cutting power to the relay. The fuse blows as a protective measure when excessive current is detected.
- 4
Check Loose or corroded connectors — Poor electrical connections at the fuel pump relay socket, fuel pump connector, or ground points create resistance and voltage drop, preventing proper circuit operation.
How to Fix It
- 1
Replace fuel pump relay
Locate the fuel pump relay in the vehicle's fuse/relay box (typically under the hood or driver's side kick panel). Remove the old relay and install a new OEM or quality aftermarket relay. Verify proper installation and test for code clearance.
- 2
Inspect and repair fuel pump wiring harness
Trace the fuel pump power supply wires from the relay to the pump. Look for chafing, cuts, or corrosion. Repair damaged insulation with electrical tape or replace the affected wire section. Ensure all connectors are fully seated and corrosion-free.
- 3
Replace blown fuel pump fuse
Locate the fuel pump fuse in the vehicle's fuse box using the owner's manual. Remove the blown fuse and replace with a new fuse of the same amperage rating. If the fuse blows again immediately, there is a short circuit requiring further diagnosis.
- 4
Clean and reseat electrical connections
Disconnect and inspect all connectors in the fuel pump circuit (relay socket, pump connector, ground points). Clean corroded terminals with a wire brush, apply dielectric grease, and firmly reconnect. This often resolves low-voltage issues caused by poor contact.
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