P0629: Fuel Pump A Control Circuit High

What does P0629 mean?

What 'fuel pump A control circuit' means differs by maker: at GM petrol 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 petrol 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. 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.

The code tells you which monitor failed, not which part is broken. Test before replacing parts.

Symptoms

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

Common causes

• High Control wire shorted to a battery feed
• Medium Relay contacts welded or relay faulty internally
• Low Moisture in the relay or fuse box
• Low Driver in the engine module shorted

Likelihood is a general estimate across vehicles; your make and model may differ.