Fuel Pump Control Circuit A Low

What is code P0628?
This is a generic OBD-II (powertrain) code applicable to most post-1996 vehicles (Ford, Dodge, Toyota, Chrysler, Jeep, Ram, Chevrolet, Nissan, Mitsubishi, Mercedes, etc.). It indicates a problem in the fuel pump control circuit “A”, specifically a low voltage situation detected.

Main Causes:

• Damaged wires or connectors in the circuit or the CAN (Controller Area Network) bus.

• Problem with the fuel pump itself.

• Cut or damaged ground wire at the control module.

• Unsecured ground strap in the control module.

• Open, shorted, or corroded wiring in the CAN bus.

• Faulty CAN bus.

• Loose harness causing chafing or broken circuits.

• High resistance in the circuit (melted/corroded connectors, internal wire corrosion).

Modules Likely to Trigger the Code:

• Powertrain Control Module (PCM) or Engine Control Module (ECM).

• Alternative Fuel Control Module.

• Fuel Injection Control Module.

• Turbo Control Module.

Common Symptoms:

• Check Engine Light (CEL) illuminated.

• Engine does not start.

• Engine misfires/stalling.

• Engine starts but stalls immediately.

• Reduced fuel economy.

• Engine cranks but does not start.

• Engine stalls once at operating temperature.

Severity:
Moderately serious problem. Although the vehicle may sometimes run, it is strongly advised against using it. An erratic fuel supply can cause severe engine damage.

Associated Codes:

• P0627: Fuel Pump Control Circuit “A” – Open

• P0628: Fuel Pump Control Circuit “A” – Low (this code)

• P0629: Fuel Pump Control Circuit “A” – High

• P062A: Fuel Pump Control Circuit “A” Range/Performance

Diagnostic (Troubleshooting) Steps:

1. Consult Technical Service Bulletins (TSBs): Check TSBs specific to your vehicle’s year, model, and engine for known solutions or specific procedures.

2. Module Scan & Visual Inspection:

   • Use an OBD-II scanner to read codes from all modules and assess the general electrical state.

   • Visually inspect connectors and wiring related to the fuel pump, CAN bus, and relevant modules (often located near the fuel tank). Look for obvious damage, corrosion, or loose wires.

3. Check Grounds:

   • Thoroughly examine the ground circuits of the involved modules (fuel pump, etc.).

   • Test using a temporary auxiliary battery ground. If the problem disappears with the auxiliary ground but returns with the original ground, the OEM ground cable is faulty.

   • Inspect ground points for corrosion (e.g., green ring on the battery + terminal). Clean or replace corroded components.

4. Check Control Circuit “A”:

   • Identify the precise circuit using a wiring diagram from the service manual.

   • Look for breaks (open circuit) by physically tracing the wire or measuring its continuity/resistance with a multimeter.

   • Look for short circuits or abnormally high resistance in the circuit using the multimeter.

   • Use a power probe to inject current and locate internal faults in the circuit.

   • Repair damaged wires by soldering or using sealed butt connectors (with heat shrink tubing).

Important:

• The code may activate after several drive cycles or immediately.

• The absence of an immediate check engine light does not mean the problem is resolved; check after a few days of use.

• This article is strictly informative. Vehicle-specific technical data and manufacturer service manual procedures should always take priority.

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Concise Summary (optional):

P0628 = Fuel Pump Control Circuit “A” – Low Voltage.
Problem: Damaged wires/connectors (especially CAN bus), faulty pump, poor grounds.
Risk: Engine may stall or be damaged → Do not drive.
Diagnosis:

1. Check manufacturer TSBs.

2. Scan modules + visual inspection of cables/connectors.

3. Check grounds (corrosion, connection).

4. Test control circuit “A” (diagram, continuity, resistance).
   ALWAYS consult the vehicle-specific service manual.