P0191

P0191-FUEL RAIL PRESSURE SENSOR CIRCUIT PERFORMANCE

For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams. Electrical Diagrams

Theory of Operation

This DTC is mapped to two different tests, a key on test and an idle diagnostic. The key-on error monitors fuel pressure voltage at key on after an 8 hour cold soak. The fuel rail pressure reading must be below a calibratable amount in order for the diagnostic to pass. The Idle Diagnostic runs whenever the engine is in an idle condition. The Engine Control Module (ECM) varies fuel pressure and monitors the final fueling and engine speed to determine if the reading from the pressure sensor is accurate. The engine must be at operating temperature and must not be in an active Aftertreatment regeneration mode in order to run this diagnostic. The engine will light the MIL lamp after the diagnostic runs and fails in two consecutive drive cycles. The ECM will turn off the MIL lamp after the diagnostic runs and passes in 4 consecutive drive cycles.

- When Monitored:
At key on, engine off and at idle conditions.

- Set Condition:
At key on, engine off the Fuel Pressure Sensor is reading above a calibrated threshold. At idle the change in final fueling value is above a calibrated threshold while the diagnostic is running.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.

1. ACTIVE DTC

NOTE: If there are any other EGR, Turbocharger, or Intake system DTCs present, repair those DTCs before proceeding.

1. Turn the ignition on.
2. With the scan tool, record all Freeze frame data.
3. With the scan tool, erase DTCs.
4. Turn the ignition off for 30 seconds.
5. Turn the ignition on for 30 seconds.
6. Start the engine and let it idle for up to one minute.
7. With the scan tool, read DTCs.

Did the DTC reset?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. FUEL RAIL PRESSURE SENSOR
1. With the scan tool, monitor the actual fuel pressure reading while the ignition is on and engine is not running.

Is the actual fuel pressure reading greater than 870 psi?

Yes

- Go To 3

No

- Go To 4

3. FUEL RAIL PRESSURE SENSOR
1. Visually inspect the fuel system components for signs of tampering, pay particular attention to the Fuel Pressure Sensor on the fuel rail and the Fuel Pressure Sensor wiring harness.

Were any signs of tampering discovered?

Yes

- Replace the Fuel Pressure Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Go To 4

4. INJECTOR LEAKAGE
1. Perform the INJECTOR RETURN FLOW TEST. Injector Return Flow Test

Does the injector drainage meet the test specification?

Yes

- Replace the Fuel Pressure Sensor.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.

No

- Repair cause of high injector leakage.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.