P0191

DTC P0191

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.

DTC Descriptor
DTC P0191
- Fuel Rail Pressure (FRP) Sensor Performance

Diagnostic Fault Information





Typical Scan Tool Data





Circuit/System Description

Idle Mode

During certain engine operating modes the engine control module (ECM) calculates an adaptation factor to align the fuel pressure regulator 2 set point with the measured fuel rail pressure. This is done to adjust for manufacturing tolerances and aging of components. If the ECM calculates an adaptation factor outside the minimum or maximum calibrated limits, DTC P0191 is set.

Post Drive Mode

During post-drive mode, the fuel pressure regulator 2 relieves any remaining fuel pressure from the rails. After a 30 second bleed-down, the fuel rail pressure sensor should read atmospheric pressure and return the proper signal voltage to the ECM. If the signal voltage is outside of the specified limits, DTC P0191 is set.

Conditions for Running the DTC

Idle Mode
* Fuel level is greater than 15 %.
* DTC P0016, P0117, P0118, P0192, P0193, P0335, P0336, P0340, or P0341 is not set.
* Engine has run above 2000 RPM for 15 s during current key cycle.
* Fuel pressure control is in fuel pressure regulator 2 mode or in combined pressure control mode.

Post Drive Mode
* Fuel level is greater than 15 %.
* DTCs P0016, P0117, P0118, P0192, P0193, P0335, P0336, P0340, or P0341 are not set.
* Fuel Temperature is greater than 0° C (32° F).
* Fuel pressure regulator 2 current is less than 1.71 A.
* Engine OFF time is greater than 30 s.
* Fault condition exists for more than 30 s.

Conditions for Setting the DTC

Idle Mode
* The ECM detects a drifted fuel rail pressure value by determining the adaptation factor of the fuel rail pressure regulator 2.
* The fuel pressure regulator 2 adaptation factor is outside the ECM's correction limits.

Post Drive Mode
* The fuel rail pressure sensor voltage is not between 0.352 V and 0.65 V.
* The fault condition exists for more than 30 s.

Action Taken When the DTC Sets

* DTC P0191 is a Type A DTC.
* If Post Drive Mode fails, engine will go to Reduced Power Mode

Conditions for Clearing the MIL/DTC

DTC P0191 is a Type A DTC.

Diagnostic Aids

* Review the freeze frame data to determine if the engine was running when the DTC set.
* Connector terminal fretting or poor connections of the wiring harness may cause this DTC to set.
* Contaminated fuel may cause this DTC to set.

Reference Information
Schematic Reference

Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
Description and Operation

Fuel System Description (Fuel System Description)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information

Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. Verify no other DTCs are set.

• If any other DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle) for further diagnosis.

2. Engine at idle, the Actual Fuel Rail Pressure should be close to the Desired Fuel Rail Pressure.
3. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Note:
* You must perform the Circuit/System Verification before proceeding with Circuit/System Testing.
* Review Freeze Frame Data to determine which operating mode the DTC was set.

1. Ignition OFF, open a fuel injector high pressure fuel line.
2. Ignition ON, verify the scan tool Fuel Pressure Sensor Voltage parameter is between 0.352-0.65 V.

• If less than the specified range, test the Fuel Rail Pressure Sensor Signal circuit and the Fuel Rail Pressure Sensor 5 Volt Reference circuit for high resistance. If the circuit tests normal, replace the B47B fuel rail pressure sensor.
• If greater than the specified range, test Fuel Rail Pressure Sensor Low Reference circuit for high resistance. If the circuit tests normal, replace the B47B fuel rail pressure sensor.

3. Install the fuel injector high pressure line.
4. Engine running, observe the scan tool Fuel Pressure Sensor Voltage parameter is less than 0.65 V within 30 seconds after ignition OFF.

• If the Fuel Pressure Voltage parameter is greater than the specified value, replace the Q18B fuel pressure regulator 2.

5. Engine at idle, command the fuel pressure incrementally through the entire fuel pressure range with a scan tool. The Actual Fuel Rail Pressure and the Desired Fuel Rail Pressure should be within 690 kPa (100 psi) for the entire fuel pressure range.

• If not within the specified range, replace the Q18B fuel pressure regulator 2.
• If the system tests normal, refer to Diagnostic Aids.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement (Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement)
* Fuel Pressure Relief Valve Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for ECM replacement, programming, and setup.