Dodge Ram Truck 1500-2500-3500. Manual — part 1108
P0628-LOW VOLTAGE DETECTED AT THE FUEL LIFT PUMP (CONTINUED)
7.
FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO OTHER CIRCUITS
Measure the resistance between the lift pump relay driver circuit in the
ECM connector and all other circuits in the ECM connectors.
Is the resistance less than 10 Ohms?
Yes
>> Repair the Fuel lift pump Relay driver circuit shorted to
another circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
No
>> Go To 8
8.
ECM
Reconnect the ECM connectors.
Turn the ignition on, engine off.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
Using the scan tool, actuate the lift pump.
Does the test light illuminate brightly?
Yes
>> Repair complete.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No
>> Replace the ECM.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
9 - 1354
ENGINE - ELECTRICAL DIAGNOSTICS - DIESEL
DR/DH
P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP
DR/DH
ENGINE - ELECTRICAL DIAGNOSTICS - DIESEL
9 - 1355
P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP (CONTINUED)
For the Engine circuit diagram (Refer to 9 - ENGINE - SCHEMATICS AND DIAGRAMS)
For a complete wiring diagram Refer to Section 8W.
•
When Monitored:
While the key is on.
•
Set Condition:
The commanded signal to the fuel lift pump relay does not match the feedback signal from the fuel lift pump
relay.
Possible Causes
DAMAGED WIRRING HARNESS
LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO GROUND
LIFT PUMP RELAY
ECM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE -
DIAGNOSIS AND TESTING)
Diagnostic Test
1.
LIFT PUMP RUNS
Remove the cover to the PDC.
Turn the ignition on, engine off.
With the scan tool, in system test actuate the lift pump relay.
Does the fuel lift pump relay click when the lift pump is actuated?
Yes
>> Test complete.
Perform Intermittent Condition test. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING)
No
>> Go To 2
2.
LIFT PUMP RELAY DOES NOT CLICK
Turn Ignition off.
Remove the lift pump relay from the PDC.
Turn the ignition on.
Connect one end of an incandescent test light to battery negative.
Connect the other end of the test light to the relay driver pin in the PDC.
With the scan tool, in system test actuate the lift pump relay.
Does the test light illuminate brightly?
Yes
>> Go To 3
No
>> Go To 5
9 - 1356
ENGINE - ELECTRICAL DIAGNOSTICS - DIESEL
DR/DH
P0629-HIGH VOLTAGE DETECTED AT THE FUEL LIFT PUMP (CONTINUED)
3.
LIFT PUMP RELAY
Install a know good relay in place of the fuel lift pump relay.
With the scan tool, in system test actuate the lift pump relay.
Does the fuel lift pump relay click when the lift pump is actuated?
No
>> Go To 4
Yes
>> Replace the lift pump relay.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
4.
FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO GROUND
Measure the resistance between battery negative and the relay driver circuit in the PDC.
Is the resistance less than 10 ohms?
Yes
>> Repair the Fuel lift pump Relay driver circuit shorted to ground.
Perform POWERTRAIN VERIFICATION TEST VER - 1 (DIESEL). (Refer to 8 - ELECTRICAL/ELEC-
TRONIC CONTROL MODULES/ENGINE CONTROL MODULE - DIAGNOSIS AND TESTING)
No
>> Go To 5
5.
FUEL LIFT PUMP RELAY DRIVER CIRCUIT SHORTED TO OTHER CIRCUITS
Measure the resistance between the lift pump relay driver circuit in the
ECM connector and all other circuits in the ECM connectors.
Is the resistance less than 10 Ohms?
Yes
>> Repair the Fuel lift pump Relay driver circuit shorted to
another circuit.
Perform POWERTRAIN VERIFICATION TEST VER - 1
(DIESEL). (Refer to 8 - ELECTRICAL/ELECTRONIC CON-
TROL MODULES/ENGINE CONTROL MODULE - DIAG-
NOSIS AND TESTING)
No
>> Go To 6
DR/DH
ENGINE - ELECTRICAL DIAGNOSTICS - DIESEL
9 - 1357
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