P0191

P0191-FUEL RAIL PRESSURE SENSOR PERFORMANCE





For complete wiring diagrams refer to Diagrams/Electrical.


Theory of Operation

"This P code 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 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.

Diagnostic Test


1. OTHER DTCS PRESENT

With the scan tool, read DTCs.

Are there any other fuel system related DTCs present?

Yes

- Repair other DTC's first.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Go To2

2. FUEL PRESSURE READING

Using the scan tool, monitor the actual fuel pressure reading while the key is on and engine is not running.

Is the actual fuel pressure reading greater than 870 psi?

Yes

- Go To3

No

- Go To4

3. FUEL RAIL PRESSURE SENSOR

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?

No

- Go To4

Yes

- Replace the Fuel rail pressure sensor.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

4. INJECTOR LEAKAGE

Perform the Injector Return Flow Test. Injector Return Flow Test

Does the injector drainage meet the test specification?

Yes

- Replace the Fuel rail pressure sensor.
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test

No

- Troubleshoot cause of high injector leakage
- Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test