OBD-II Code P0628 — What It Means & How to Fix It

What Does This Error Mean?

P0628 means the fuel pump control circuit is reading a voltage that is too low. The ECM monitors the voltage on the fuel pump control line. Low voltage on this circuit often means a short to ground somewhere between the ECM and the pump relay or module. The fuel pump may not operate correctly, causing hard starts, stalling, or a no-start condition. This requires diagnosis and repair to restore proper fuel delivery.

Affected Models

All vehicles 1996+
Common in GM cars and trucks
Common in Ford vehicles
Common in Chrysler, Dodge, and Jeep vehicles
Common in vehicles with electronic fuel pump control circuits

Common Causes

Short to ground on the fuel pump control wire between the ECM and relay or module
Faulty fuel pump relay with a failed coil drawing too much current
Damaged wiring harness with insulation worn through and contacting the chassis
Corroded or damaged fuel pump relay connector reducing signal voltage
Internal ECM driver failure causing the output to read low

How to Fix It

Remove the fuel pump relay from the fuse box. With the relay removed and key on, measure voltage at the relay control circuit pin. Low or zero voltage with the relay removed confirms the wiring or ECM has an issue.

Normal control voltage with the relay removed and key on should be near 12V on the coil supply pin.
Check the relay control wire for a short to ground. With the relay removed and key off, measure resistance between the control wire and vehicle chassis ground. Anything under 1000 ohms suggests a short.

A short to ground pulls the voltage down on the control circuit.
Inspect the wiring harness along its full routing from the relay socket back to the ECM. Look for any areas where insulation has worn through against sharp metal edges.

Pay special attention to areas near brackets, body clips, and any heat sources.
Swap the relay with a matching one from another circuit and see if the behavior changes. A relay with an internal short can cause low voltage on the control circuit.

Relays are cheap. Swapping to test takes less than 60 seconds.
If wiring and relay check out, the ECM output driver may have an internal short. Have this tested by a shop before replacing the ECM — it is the most expensive component in this circuit.

ECM failures that cause low output voltage are less common than wiring shorts. Do not skip the wiring check.

When to Call a Professional

Fuel pump relay and wiring repairs are manageable for most DIYers. Relays cost $10 to $25. Wiring repair at a shop is $75 to $200 depending on the fault location. Fuel pump replacement if the pump has been damaged costs $200 to $500 for parts plus labor. ECM repair or replacement if the driver has failed costs $200 to $600 or more.

Frequently Asked Questions

Can the car run with P0628?

Maybe, but poorly. If the fuel pump is receiving reduced power due to the low voltage condition, it may still run but with insufficient fuel pressure. This causes rough running, hesitation, or stalling at higher speeds. A complete loss of pump control causes a no-start.

How do I know if the fuel pump is actually running?

Turn the key to On (not Start) and listen for a brief hum from the fuel tank — about 2 seconds. If you hear nothing, the pump is not running. You can also use a fuel pressure gauge to check if pressure builds at the fuel rail.

Is P0628 the same as a bad fuel pump?

Not directly. P0628 is about the control circuit voltage, not the pump itself. The pump could be perfectly fine but not running due to a wiring issue. Always check the circuit before replacing the pump — it is a more expensive part.