P0629

Diagnostic Chart:

Schematic:

The fuel pump relay is located in the underhood fuse block (UHFB). The ECM controls the fuel pump motor by supplying ignition voltage to the fuel pump relay coil whenever the engine is cranking or running. When the fuel pump relay is commanded Off (circuit NOT supplied ignition voltage), the voltage level at the ECM should be low (ground). When the fuel pump relay is commanded On (circuit supplied ignition voltage), the voltage level at the ECM should be high (ignition voltage). The ECM uses a very high resistance bypass resistor that is tied internally from ignition voltage to the fuel pump relay coil circuit. This allows the ECM to detect a high voltage condition if circuit 465 is open when the fuel pump relay is not being supplied ignition voltage. DTC P0629 will set if the ECM detects a high voltage condition on the fuel pump relay coil control circuit when the fuel pump relay is commanded Off with ignition On and engine NOT running; OR during engine crank or run when the ECM is momentarily turning off the fuel pump relay to check for a high voltage condition.

DTC PARAMETERS
DTC P0629 will set if fuel pump relay feedback voltage is greater than 6.6 volts when fuel pump relay is commanded Off when:
^ Condition exists for longer than 0.5 seconds
^ Engine is NOT cranking or running with ignition On
^ Main relay voltage is between 8.0 and 18.0 volts

OR

^ Condition exists for longer than 0.5 seconds
^ ECM is momentarily turning off the fuel pump relay for 0.8 seconds. The ECM can perform this up to 5 times per ignition cycle.
^ Engine speed is greater than 40 rpm
^ Main relay voltage is between 10.5 and 18.0 volts

DTC P0629 diagnostic runs continuously once the above conditions have been met.

P0629 is a type C DTC.

DIAGNOSTIC AIDS

IMPORTANT: The ECM will only energize the fuel pump relay when the engine is cranking or running. If the ignition is turned On and the engine is not cranking, the fuel pump will NOT run.

Eight or more volts from the ECM on circuit 465 with the ignition On, engine Off is normal. This voltage should NOT light a test light.

An intermittent open or short to voltage on circuit 465 can set this DTC. Use Scan tool to command the FUEL PUMP RELAY On while wiggling circuit 465. The fuel pump should stop running if an open occurs or continues to run if a short to voltage occurs.

Fuel pump relay coil resistance: 70-115 ohms