P0628
PowertrainFuel Pump A Control Circuit Low
The fuel pump control circuit feeds power to your fuel pump, and the ECU watches the voltage on that circuit to make sure the pump is getting what it needs. P0628 means the ECU has seen the voltage drop too low on the control side, so it's flagging an electrical problem rather than a knackered pump. Most of the time this points to wiring, a tired relay, or a poor earth somewhere between the module and the tank. If the pump stops getting reliable power, you get hard starting, stalling, or a car that won't fire up at all.
ⓘ Information only. This page provides general educational information about fault code P0628. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0628 mean?
P0628 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Fuel Pump A Control Circuit Low.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, often before you notice anything else wrong
- • Hard starting, especially first thing in the morning or after the car's sat overnight
- • Stalling at idle or as you pull away from a junction
- • Hesitation or a flat spot under acceleration as fuel delivery drops out
- • Fuel gauge bouncing about or reading nonsense on some cars
- • Total no-start in the worst cases, where the pump gets no power at all
Possible causes
Causes commonly associated with P0628, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Damaged or corroded wiring in the fuel pump control circuit. The harness near the tank gets road spray and salt, and connectors give up
- 2. Failing fuel pump relay with burnt or pitted contacts. These are cheap to test and a common culprit
- 3. Poor earth at the pump or the control module. A high-resistance ground will pull the circuit voltage down and set this code
- 4. Loose or corroded connector at the tank, often hidden under carpet or a boot panel
- 5. Low battery voltage or a weak charging system dragging the whole circuit down
- 6. Failing fuel pump or pump driver module, less common than the wiring faults but it does happen
- 7. CAN bus communication faults on cars that control the pump over the network, rare but worth ruling out
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Read all stored codes and the freeze frame data. If you've got low system voltage codes or a separate pump driver code alongside, that steers the diagnosis straight away
- 2. Check the battery and charging system first. A flat or failing battery throws up low-voltage faults across the board and will waste your time if you skip it
- 3. Test the fuel pump relay. Swap it with an identical relay from elsewhere in the fuse box if you can, or check it with a multimeter for proper switching
- 4. Get under the back of the car and inspect the harness and connector at the tank. Look for green corrosion, chafed wires, and pins pushed back out of the plug
- 5. Back-probe the pump connector with the ignition on and the pump priming. You want to see close to battery voltage. A big drop tells you the supply or earth side is at fault
- 6. Check the earth point properly. Clean it up and run a temporary jumper to a known-good ground to see if the reading comes good. Only condemn the pump or driver module once the wiring, relay and earths all check out
Common questions about P0628
Will my car pass its MOT with this code stored? +
The code on its own isn't a fail, but if the engine warning light is lit when the tester looks at the dash, that's an automatic fail under the current rules. The MOT checks the MIL state, not your scan tool. So you need the underlying fault sorted and the light cleared before the test. There's also the practical problem that a P0628 can leave the car stalling, and a car that won't run properly isn't getting through the emissions side either.
What am I likely to pay to get this fixed? +
It swings hugely depending on what's actually wrong. A fuel pump relay is usually £15 to £40 for the part and barely any labour. A wiring or connector repair at an independent garage might be £60 to £200 once they've spent time tracing it. If it turns out the pump or driver module is gone, you're looking at £250 to £600 fitted at an independent, and a fair bit more at a main dealer where the pump module and labour both cost more. Get a garage to confirm the cause before you authorise a pump, because that's the expensive guess to get wrong.
How do I work out whether it's the wiring, the relay, or the actual pump? +
Work outward from the cheap stuff. Sort the battery and charging voltage first, then test or swap the relay since it's the most common quick win. After that, back-probe the pump connector with the ignition on. Near battery voltage there means the supply is fine and you should be looking at the earth or the pump itself. A low or missing reading means the fault is upstream in the wiring or relay circuit. Wiggle-test the harness near the tank while watching live voltage, because an intermittent connector will move the reading as you flex it. Only after all that does the pump become the likely answer.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →