P0628 – Fuel Pump “A” Control Circuit Low

System: Powertrain | Standard: ISO/SAE Controlled | Fault type: Circuit Low | Location: Designator A

Definition source: SAE J2012/J2012DA (industry standard)

P0628 is a powertrain diagnostic trouble code that indicates the engine control module (or another powertrain controller) has detected a low condition in the Fuel Pump “A” control circuit. In practical terms, the module expected to see the fuel pump control circuit behave normally when commanding the pump on or off, but the monitored electrical feedback for that control path stayed below the acceptable range for the strategy being used. Exact circuit layout and monitoring behavior vary by vehicle (for example, relay-controlled pumps versus electronically modulated pump drivers), so always confirm the wiring diagram, connector views, and test conditions in the service information before testing or replacing parts.

What Does P0628 Mean?

P0628 means the powertrain controller has identified “Fuel Pump ‘A’ Control Circuit Low.” Per standardized DTC structure practices, this is an electrical fault classification focused on a low-input/low-signal condition in the control circuit that operates the fuel pump identified as “A” (the specific meaning of “A” varies by vehicle). The code does not, by itself, prove the fuel pump is mechanically bad or that fuel pressure is incorrect; it indicates the controller is seeing an abnormally low electrical state in the commanded/monitored fuel pump control path. Accurate diagnosis requires verifying the circuit’s power, ground, command, and feedback behavior using the vehicle’s service information and test procedures.

Quick Reference

• Subsystem: Fuel Pump “A” control circuit (pump command/driver, relay control, and related wiring/connectors).
• Common triggers: Control circuit short-to-ground, open power/feed to the control side, excessive resistance causing voltage drop, or a driver/relay that cannot pull the circuit to the expected state.
• Likely root-cause buckets: Wiring/connector faults, power/ground distribution issues, fuel pump relay or pump control module faults (if equipped), fuel pump driver circuit fault in the controller.
• Severity: Potential no-start, stall, or reduced engine performance; may become a safety concern if stalling occurs.
• First checks: Battery voltage and grounds, fuses feeding the fuel pump control path, visible harness damage near pump/relay/control module, connector pin fit/corrosion, and whether the pump can be commanded on with a scan tool (if supported).
• Common mistakes: Replacing the fuel pump first without confirming a circuit-low condition, skipping voltage-drop tests under load, and overlooking relay/control-module power and ground integrity.

Theory of Operation

The fuel pump is typically powered through a high-current path and controlled by a low-current command path. Depending on design, the controller may energize a fuel pump relay, send a command to a separate pump control module, or directly drive the pump using an internal driver. The controller also monitors the control circuit (and sometimes a feedback/diagnostic line) to confirm the commanded state is actually being achieved.

For a circuit-low fault, the controller detects that the control circuit remains too low when it should be higher (or fails to transition as expected) during a command. Common electrical reasons include a short-to-ground on the control wire, an open in the power/feed to the control side, or excessive resistance in connectors/grounds that pulls the circuit down under load. The exact monitor logic and enabling conditions vary by vehicle.

Symptoms

• No-start: Engine cranks but does not start if the pump is not being commanded or cannot run.
• Stall: Engine may stall if fuel delivery stops while driving or at idle.
• Long crank: Extended cranking time before starting due to delayed/insufficient pump operation.
• Hesitation: Poor response on acceleration if fuel delivery becomes intermittent.
• Reduced power: Limited performance under load when fuel supply is unstable.
• Warning light: Malfunction indicator lamp illuminated with stored P0628 and possibly related fuel delivery codes.
• Intermittent operation: Symptoms may come and go with vibration, temperature, or harness movement.

Common Causes

• Short-to-ground in the fuel pump “A” control circuit wiring (rubbed-through insulation, pinched harness)
• High resistance or poor connection in the fuel pump “A” control circuit (corrosion, spread terminals, poor pin fit)
• Open power feed to the fuel pump control side (blown fuse, faulty relay contacts, loose power connection) causing the control circuit to be pulled low
• Faulty fuel pump relay (if used) with a shorted coil, stuck contacts, or internal leakage that drags the control circuit low
• Fault in the fuel pump driver/control module (if used) that pulls the commanded/feedback line low
• Fuel pump “A” actuator circuit issue at the pump connector (shorted component, damaged connector, water intrusion causing low signal)
• Poor ground path in the fuel pump circuit that creates abnormal current flow and a low signal condition during monitoring
• PCM/ECM driver or internal circuit fault affecting the fuel pump “A” control output (less common; verify all external causes first)

Diagnosis Steps

Tools typically needed include a scan tool capable of reading freeze-frame data and live data (and ideally commanding the fuel pump ON where supported), a digital multimeter, and a test light suitable for automotive circuits. A wiring diagram and connector pinout for the fuel pump “A” control circuit are essential because routing and architecture vary by vehicle. Back-probing tools and basic harness repair supplies are also helpful.

1. Confirm the DTC and capture data: Scan for codes, record freeze-frame data, and note any related fuel, power, or communication codes. Clear codes and see if P0628 resets immediately or only after a key cycle/drive cycle.
2. Check for obvious fuel pump operation issues: Determine whether the vehicle has a no-start, extended crank, stall, or normal operation. If the engine will not start, prioritize power/feed and control-circuit checks before extended testing.
3. Identify the circuit design (varies by vehicle): Using service information, confirm how “Fuel Pump A” is controlled (relay-controlled, dedicated driver module, integrated module). Identify the exact control circuit pin(s) at the PCM/ECM, relay/driver, and pump connector.
4. Do a visual inspection first: Inspect the harness routing to the relay/driver and fuel pump. Look for chafing, pinch points, aftermarket splices, melted conduit, and connector damage. Closely inspect terminals for corrosion, moisture, and looseness.
5. Perform a wiggle test while monitoring: With the scan tool on live data (and/or while attempting to command the pump ON if supported), gently wiggle the harness and connectors for the fuel pump “A” control circuit. If the status changes or the code resets, isolate the section that reacts to movement.
6. Verify power supply and grounds to the fuel pump system: Check the relevant fuses and any fuel-pump relay power feeds under load. Confirm ground integrity for the pump/driver/relay circuits. If a ground is suspected, use a voltage-drop test across the ground path while the circuit is operating to identify excessive resistance.
7. Check the control circuit for short-to-ground: Key OFF and circuit de-energized as required by service info, disconnect the PCM/ECM connector and the relay/driver/pump side as needed to isolate the circuit. Test the fuel pump “A” control wire for continuity to ground. If it shows an unintended path to ground, locate the short (harness damage, water intrusion, or a shorted component pulling it low).
8. Check for excessive resistance/poor connections in the control circuit: With connectors disconnected, measure continuity end-to-end of the control circuit and perform point-to-point checks across intermediate connectors. Inspect for partial opens and high resistance from corrosion or poor terminal tension. Repair/replace terminals or wiring as needed.
9. Test the relay/driver function (if equipped): Verify the relay coil/control side is not internally shorted and that contacts are not sticking or leaking in a way that drags the control circuit low. For a driver module, verify its power/ground supplies and that it does not pull the control line low with the module disconnected from the load side, per service info.
10. Command the fuel pump and monitor response: If the scan tool supports bi-directional control, command the pump ON and observe related PIDs (command, feedback/status if available). Compare behavior with the electrical tests performed. If the control circuit remains low when commanded, re-check for shorts/voltage drops and confirm the module’s ability to drive the circuit.
11. Prove the repair with a repeatable test: After repairs, clear codes and run the enable conditions (key cycles and/or road test) while live-data logging the fuel pump “A” control state and system voltage. Ensure P0628 does not return and that fuel pump operation is stable under vibration and load.

Professional tip: Treat “circuit low” as an electrical condition to be proven, not a part to be replaced. The fastest path is usually isolating the control circuit into sections (PCM/ECM side, intermediate connectors, relay/driver, pump connector) and repeating the same checks: short-to-ground, voltage-drop under load, and connector integrity. Log live data during a wiggle test to catch intermittent low events that won’t appear during static checks.

Possible Fixes & Repair Costs

Repair costs for P0628 vary widely because the underlying cause can range from simple wiring issues to module or driver faults. Total cost depends on accurate diagnosis, component access, parts availability, and the amount of electrical testing and rework required.

• Repair or replace damaged wiring in the fuel pump “A” control circuit after confirming a circuit-low condition with testing
• Clean, secure, and re-pin poor terminal connections (corrosion, spread pins, loose locks) at the fuel pump, relay/module, or control module connectors
• Restore proper power feed and ground integrity (repair open feeds, poor grounds, or high-resistance splices) found during voltage-drop testing
• Replace a faulty fuel pump relay or external control device (where used) only after verifying control-circuit command and load response
• Replace a faulty fuel pump control module (where used) after confirming correct inputs/outputs and that the low condition persists
• Replace the fuel pump assembly only if testing shows the pump/load is causing the control circuit to be pulled low or drawing abnormal current (varies by vehicle)
• Repair control module driver/control-side faults or update/reprogram control software only when service information supports it and circuit testing is conclusive

Can I Still Drive With P0628?

Driving with P0628 is risky because a fuel pump control circuit low condition can lead to intermittent fuel delivery, hesitation, stalling, or a no-start. If the engine stalls, starts and dies, loses power unexpectedly, or warning indicators appear related to reduced power or critical systems, do not drive—have the vehicle towed and diagnosed. If it seems to run normally, limit driving to essential trips only and avoid high-speed or heavy-load conditions until the fault is verified and repaired.

What Happens If You Ignore P0628?

Ignoring P0628 can allow an intermittent circuit-low condition to worsen into a repeat stall or a no-start, potentially leaving the vehicle stranded. Continued operation with unstable fuel pump control may also cause extended cranking, inconsistent performance, and repeated fault storage, complicating diagnosis by adding secondary codes and masking the original electrical issue.

Related Pump Fuel Codes

Compare nearby pump fuel trouble codes with similar definitions, fault patterns, and diagnostic paths.

• P2929 – Fuel Pump Secondary Circuit Low
• P025C – Fuel Pump Control Module Control Circuit Low
• P0192 – Fuel Rail Pressure Sensor Circuit Low
• P2908 – Exhaust Aftertreatment Fuel Injector Circuit Low
• P2060 – Reductant Injection Air Pump Control Circuit Low
• P0698 – Sensor Reference Voltage “C” Circuit Low

Key Takeaways

• P0628 indicates the fuel pump “A” control circuit is being detected as low by the powertrain control system.
• Common electrical drivers for a circuit-low fault include short-to-ground, open power feed, poor grounds, or high resistance causing voltage drop.
• Confirm the fault with targeted circuit tests (including voltage-drop and connector inspection) before replacing components.
• Intermittent stalls or a no-start are possible; treat drivability changes as a safety concern.
• Repair should focus on the verified cause: wiring/terminals, relay/control device, module, or pump/load as supported by testing.

Vehicles Commonly Affected by P0628

• Vehicles that use an electronically controlled fuel pump “A” control circuit rather than a purely mechanical fuel delivery strategy
• Platforms with a dedicated fuel pump control module that modulates pump operation (design varies by vehicle)
• Vehicles where the powertrain control module directly commands a fuel pump relay or driver circuit
• High-mileage vehicles with increased likelihood of harness wear near the fuel tank area
• Vehicles operated in corrosive environments where connector/ground degradation is more common
• Vehicles with recent electrical repairs, collision work, or aftermarket wiring changes near the fuel pump circuit
• Vehicles with frequent vibration exposure that can loosen terminals or stress harness routing
• Vehicles with underbody exposure to road debris affecting harness protection

FAQ

Does P0628 mean the fuel pump is bad?

No. P0628 only states that the fuel pump “A” control circuit is being detected as low. That can be caused by wiring damage, a short-to-ground, a weak power feed, a poor ground, a relay/control device issue, a module driver issue, or a pump/load problem. Testing is required to confirm the root cause.

What electrical problems most often cause a “control circuit low” condition?

Typical causes include a short-to-ground on the control circuit, an open or weak power feed to the control side, poor ground integrity, high resistance at connectors/splices that creates excessive voltage drop under load, or a failing relay/control device that cannot supply the circuit correctly. The exact architecture varies by vehicle.

Can a bad relay cause P0628?

Yes, on vehicles that use a fuel pump relay or similar external control device. If the relay contacts are resistive, the coil control path is compromised, or the relay socket terminals are loose/corroded, the control circuit may be pulled low or fail to reach the expected state. Confirm with circuit testing rather than replacing parts by assumption.

Will clearing the code fix P0628?

Clearing the code only erases stored information; it does not correct the electrical condition that set the fault. If the underlying circuit-low condition remains, P0628 will likely return once the monitor runs again. Use the freeze-frame and live data (if available) to help reproduce the conditions under which it set.

What should I check first before replacing parts?

Start with the basics: inspect related fuses and power feeds, verify ground connections, and closely examine connectors and harness routing for damage or corrosion near the fuel pump and control components. Then perform voltage-drop tests under load and a wiggle test while monitoring live data to identify intermittent faults.

Consult the vehicle’s service information to identify the exact fuel pump “A” control circuit path and test points before beginning repairs.