P0191

P0191-FUEL RAIL PRESSURE SENSOR CIRCUIT PERFORMANCE





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

Theory of Operation

This DTC is mapped to an idle diagnostic, and runs only at idle. The key-on error monitors fuel pressure voltage at key on after an eight hour cold soak. The Powertrain Control Module (PCM) varies fuel pressure and monitors the final fueling and engine speed to determine if the rate of change of fueling with respect to rate of change of pressure is with in the normal operation limits of the pressure sensor. The engine must be at operating temperature and must not be in an active after treatment regeneration mode in order to run this diagnostic. The idle monitor runs once per drive cycle and the PCM will light the MIL lamp after the diagnostic runs and fails in two consecutive drive cycles. The PCM will turn off the MIL lamp after the diagnostic runs and passes in four consecutive drive cycles.

- When Monitored:
Engine running at idle.

- Set Condition:
At idle, the rate of change in fueling with respect to the rate of change of pressure is below the calibrated fail high threshold or above the calibrated fail low threshold while the monitor was 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 75 seconds.
5. Start the engine and let it idle for up to one minute.
6. 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 above 870 psi?

Yes

- Go To 3

No

- Go To 4

3. VISUALLY INSPECT THE 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. CHECK THE INJECTOR RETURN FLOW
1. Injector Return Flow Test Perform the 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 Fuel Injector leakage.
- Perform the POWERTRAIN VERIFICATION TEST - 6.7L. Powertrain Verification Test.