P0251
P0251-INJECTION PUMP FUEL VALVE FEEDBACK
For complete wiring diagrams refer to Diagrams/Electrical.
Theory of Operation
The Fuel Control Actuator (FCA) is an electronically controlled solenoid valve. The circuit is a PWM driver in the ECM that controls the FCA . The actuator is grounded in the ECM. The ECM varies the current to this valve to provide the correct fuel flow to the high pressure pump based on operating conditions. The FCA is a normally open valve. High circuit resistance may cause fuel pressure to be higher than commanded at light loads. The ECM illuminates the MIL lamp immediately after the diagnostic runs and fails. During this time the customer may experience low power. The ECM turns off the MIL lamp after the diagnostic runs and passes in 4 consecutive drive cycles.
- When Monitored:
When the ignition is on.
- Set Condition:
The ECM detects a discrepancy between the PWM supplied to the Electronic Fuel Control Actuator and the PWM returned from the Electronic Fuel Control Actuator.
Possible Causes:
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
1. ACTIVE DTC
Ignition on, engine not running.
Record freeze frame data and clear DTCs.
Test drive the vehicle under various load conditions.
Turn the ignition on.
With the scan tool, read DTCs.
Did the DTC return?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION - 6.7L Diagnostic Procedure. Component Tests and General Diagnostics
2. (K365) FUEL CONTROL ACTUATOR DRIVER CIRCUIT SHORTED TO VOLTAGE
Turn the ignition off.
Disconnect the Fuel Control Actuator harness connector.
Turn the ignition on.
Measure the voltage of the (K365) FCA Driver circuit at the FCA harness connector.
NOTE: The (K365) FCA Driver circuit will read approximately six volts at initial key on and then drop to approximately three volts.
Is the voltage reading near battery voltage?
Yes
- Repair the short to voltage in the (K365) FCA Driver circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No
- Go To 3
3. (K366) FUEL CONTROL ACTUATOR RETURN CIRCUIT SHORTED TO VOLTAGE
Measure the voltage of the (K366) FCA Return circuit at the FCA harness connector.
NOTE: The (K366) FCA Return circuit should not have voltage present.
Is there any voltage present?
Yes
- Repair the short to voltage in the (K366) FCA Return circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No
- Go To 4
4. (K365) FUEL CONTROL ACTUATOR DRIVER CIRCUIT OPEN/HIGH RESISTANCE
Turn the ignition off.
Disconnect the ECM C1 harness connector.
NOTE: Check connectors - Clean/repair as necessary.
Measure the resistance of the (K365) FCA Driver circuit between the Fuel control actuator harness connector and the ECM C1 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 5
No
- Repair the (K365) Fuel Control Actuator Driver circuit for an open or high resistance.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
5. (K366) FUEL CONTROL ACTUATOR RETURN CIRCUIT OPEN/HIGH RESISTANCE
Measure the resistance of the (K366) FCA Return circuit between the Fuel Control Actuator harness connector and the ECM C1 harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 6
No
- Repair the (K366) Fuel Control Actuator Return circuit for an open or high resistance.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
6. (K365) FUEL CONTROL ACTUATOR DRIVER CIRCUIT SHORTED TO GROUND
Measure the resistance between ground and the (K365) FCA Driver circuit at the FCA harness connector.
Is the resistance above 10k Ohms?
Yes
- Go To 7
No
- Repair the short to ground in the (K365) FCA Driver circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
7. (K365) FCA DRIVER CIRCUIT SHORTED TO THE (K366) FCA RETURN CIRCUIT
Measure the resistance between the (K365) FCA Driver circuit and the (K366) FCA Return circuit at the Fuel Control Actuator harness connector.
Is the resistance above 10k Ohms?
Yes
- Go To 8
No
- Repair the short between the (K365) FCA Driver circuit and the (K366) FCA Return circuit.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
8. FUEL PRESSURE
Reconnect the Fuel Control Actuator harness connector.
Reconnect the ECM C1 harness connector.
Turn the ignition on and clear any DTCs.
Start the engine.
With the scan tool watch fuel pressure vs. setpoint with the engine at idle.
Is the pressure within ± 500 psi of set point?
If psi is within 500 psi
- Document DTC and freeze frame data and attempt to duplicate complaint.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
If the psi is higher than setpoint
- Go To 11
If the psi is lower than setpoint
- Go To 9
9. LIFT PUMP
Perform the lift pump flow test. Component Tests and General Diagnostics
Did the LIFT PUMP FLOW TEST pass?
Yes
- Go To 10
No
- Repair as necessary.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
10. INJECTOR RETURN FLOW
Perform the Injector return flow test. Component Tests and General Diagnostics
Did the INJECTOR RETURN FLOW TEST pass?
Yes
- Go To 11
No
- Repair as necessary.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
11. FUEL CONTROL ACTUATOR
Reconnect the ECM harness connectors.
Connect an incandescent test light across the Fuel Control Actuator driver pin and the Fuel Control Actuator return wire at the fuel control actuator connector.
Turn the ignition on, engine not running.
Observe the test light.
The ECM will perform a self test of the circuit which should momentarily flash the test light brightly, one time, approximately 20 seconds after being connected.
NOTE: Compare test light brightness to that of a direct connection to the battery.
Did the light flash brightly?
Yes
- Replace the Fuel Control Actuator.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test
No
- Replace and program the Engine Control Module (ECM).
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test