P0629–P2634 Fuel Pump A Control Circuit High

Which code is which

Same fault, different cylinder or bank — diagnosed the same way. Several set together usually means one shared cause.

The definition

P0629: Fuel Pump A Control Circuit High.

P0629 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

1. Unplug the sensor and check whether the signal falls. If it stays high, suspect the wiring rather than the sensor.
2. Check the earth path - a missing earth makes a sensor read high.

What actually causes this on a VAG

Official definition: Fuel Pump "A" Control Circuit High. On many modern VW, Audi, SEAT and Skoda models the in-tank fuel pump is not simply switched on and off - a fuel pump control module varies its output on the engine ECU's instruction. This code means the ECU has seen more voltage on that control line than it expects: something is holding the line up, or nothing is pulling it down. Note that a straightforwardly broken or open circuit has its own separate code (P0627), so 'high' points at voltage on the wire rather than a snapped one. Take the symptoms seriously. This can present as nothing at all, but it can also cause long cranking, a stumble under load, or the engine cutting out - and an engine that dies at a junction or on a motorway takes your power steering assist and brake servo with it. If the car has already stalled or hesitated, stop driving it and get it diagnosed rather than running it until it fails. Many of these cars have a fuel supply module you can scan in its own right (address 58), which gives far better information than the generic code.

Most likely causes, in order

1. Damp or corroded connector at the fuel pump control module. The module commonly sits under a rear seat cushion or in the boot floor area near the tank - exactly where water gets in from a leaking door seal, sunroof drain or boot seal. Lifting the cushion or boot floor and looking for damp, staining or green terminals costs nothing and is the first thing to do. If you find water, find the leak as well.
2. Fuel pump relay, fuse, or a burnt relay socket. Not every model uses the same arrangement, but where a relay is involved, burnt or spread contacts in the socket are a common and cheap fault, and VAG lists fuel pump relay short-to-positive and short-to-earth faults in its own tables. Check the relevant fuse, and swap in a known-good relay of the same part as a quick test. A relay socket with heat-discoloured terminals is worth replacing outright.
3. The fuel pump control module itself. These modules fail from heat as well as moisture - a module that is extremely hot to the touch after a run is a recognised sign. Damage inside the module can leave the control line sitting high. It is a mid-priced part and far cheaper than a pump, but check its plug, earth and supply before condemning it.
4. Wiring or earth between the ECU, the module and the pump. A chafed section touching a live, a broken core or a poor earth point produces this reading. Check where the loom passes through a body grommet, under a seat rail or under carpet, and anywhere previous work - a stereo, an alarm, a tow bar, a seat - has disturbed it.
5. The in-tank pump itself, or the ECU output. Both can set this, and both are the expensive answers. Neither should be considered until the module, its connector, the earth, the relay and the wiring have been checked and cleared. A workshop can watch fuel pressure and the pump's commanded value live to tell whether the pump is actually being asked to run.

Worth knowing: Do not let anyone start by replacing the in-tank pump. On these cars the control module and its connector - usually reachable under the rear seat or boot floor - fail far more often than the pump and cost a fraction as much, and the checks above are mostly free. If water is found, fix the leak too, or the replacement will go the same way. Two cautions: this is a pressurised fuel system, so anything beyond lifting a seat cushion to inspect a plug means depressurising the system, no ignition sources anywhere near the work, and a workshop if you are not set up for it - and because a fault here can stall the engine, treat a car that has already cut out as off the road until it is sorted.

Common questions

What does P0629 mean?

P0629 means Fuel Pump A Control Circuit High. The voltage on this circuit is sitting near battery voltage. Typically a short to a positive feed, or a disconnected sensor floating high.

Can I drive with P0629?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

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