graynn

Went out to start my truck last week and it started, then died after about 15-20 seconds running. I drained the water separator/filter and changed the filter. Truck started and died immediately. What I noticed was the fuel lift pump was not running as it usually does after changing the filter. I have done some investigating and found these pumps are prone to failure. Its a 2003 with the pump mounted on the back of the filter, and when it fails it just goes without warning. I checked the codes and I have P0629. The threads I have read said the a P0628 code indicates a failed pump. What is the difference between the two, and where should I start troubleshooting. I'd like to start with the voltage at the lift pump. I assume it is a 2 pin connector. Which pin is ground and which is power? Should I expect 12 volts when I turn on the key? Any help would be greatly appreciated.

P0628 Fuel Pump Relay Circuit Low, or Fuel Lift Pump Control Circuit Low
P0629 Fuel Pump Relay Circuit High, or Fuel Lift Pump Control Circuit High

booman70

do you have a fuel pressure gauge? How long does the pump run if you just turn the key don't start? I think when you said it's not running as loing as it usually does you probably answered you own question I bet it is a bad or dieing pump. If you fill in your sig it might help out so people know what ya got.

vzdude

P0629 High Voltage Detected At The Fuel Lift Pump
Symptom:
P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP
When Monitored and Set Condition:
P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP
When Monitored: While the key is on.
Set Condition: The commanded signal to the lift pump does not match the feedback
signal from the lift pump.
POSSIBLE CAUSES
LOOSE CONNECTION
SUPPLY CIRCUIT SHORTED TO VOLTAGE
SUPPLY CIRCUIT SHORTED
LIFT PUMP
ECM
TEST ACTION APPLICABILITY
1 With the DRBIIIt, in system test actuate the lift pump.
Does the lift pump run?
ENGINE- 5.9L
CUMMINS 24V
DIESEL
Yes ! Go To 2
No ! Test Complete.
2 Lift pump actuation still running.
While the lift pump is running, wiggle the wiring harness and connectors throughout
the circuit.
Does this interrupt the pump operation?
ENGINE- 5.9L
CUMMINS 24V
DIESEL
Yes ! Repair the loose connection.
No ! Go To 3
3 Disconnect the ECM harness connectors.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance between the lift pump supply circuit of the lift pump
connector and battery negative.
Is the resistance greater than 100k Ohms?
ENGINE- 5.9L
CUMMINS 24V
DIESEL
Yes ! Go To 4
No ! Repair the supply circuit shorted to voltage.
4 Measure the resistance between the lift pump supply circuit and all other circuits in
the ECM harness connectors.
Is the resistance greater than 100k Ohms?
ENGINE- 5.9L
CUMMINS 24V
DIESEL
Yes ! Go To 5
No ! Repair the supply circuit shorted to another circuit.
190
DRIVEABILITY - DIESEL
TEST ACTION APPLICABILITY
5 Reconnect the disconnected Lift pump harness connector.
Reconnect the ECM harness connectors.
Turn the ignition on.
With the DRBIIIt, read DTCs while disconnecting the lift pump.
Did P0628 set?
ENGINE- 5.9L
CUMMINS 24V
DIESEL
Yes ! Replace the lift pump.
No ! Replace the ECM
191
DRIVEABILITY - DIESEL
P0629-HIGH VOLTAGE DETECTEDAT THE FUEL LIFT PUMP—Continued