EngineLightCodes
Powertrain code

P0629 Fuel Pump A Control Circuit High

Severity
Fix soon
Typical repair cost
$20–$550
Do it yourself
Possible, medium
Shop time
0.5–3 hours

What 'fuel pump A control circuit' means differs by maker: at GM gasoline engines it is the control line from the engine module to the fuel pump relay (high-side driver), at GM's LML diesel the lift pump, at Ford gasoline engines with a pump driver module the secondary circuit from that module to the pump (reported as a duty cycle on a monitor line), and at Ford's 6.7 L diesel (F-650/750) the high or low side of the pump relay.

How the engine computer detects it

P0629 means a short to battery voltage: GM detects voltage at the output while the driver is off (8 of 10 samples at 250 ms, two trips in 2018); because the driver hardware cannot always separate open circuit and short to voltage, P0627 may set as well. Ford's 6.7 L diesel reports a short to voltage on the high side of the pump relay within 0.2 s. If the pump can no longer be switched off it may keep running after switch-off and drain the battery.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Pump runs constantly or after switch-off
  • Battery drained
  • Possibly no start
  • Check engine light on

Common causes

  1. Control wire shorted to a battery feed Most likely
  2. Relay contacts welded or relay faulty internally Possible
  3. Moisture in the relay or fuse box Less likely
  4. Driver in the engine module shorted Less likely

How to diagnose P0629

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: fuel pump relay, fuel pump driver module, fuel pump, engine control module.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
6
Computer and output circuits
29
Specific fault

Questions drivers ask

Can I drive with code P0629?

Usually yes for a short time, if the car drives normally, the temperature gauge reads normal and the check engine light is steady. If the light flashes, the engine loses power or overheats, or other warning lights come on, pull over and have it checked.

Will my car pass an emissions inspection with P0629?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

Will P0629 clear by itself?

The light can go off after several drive cycles without the fault, but the code returns if the cause is still there. After a repair, the readiness monitors need a full drive cycle before an inspection.

Can I fix P0629 myself?

Often yes, with an OBD-II scanner and basic tools. Difficulty: medium. Start with the cheapest checks before replacing expensive parts.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.