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 Descriptors
DTC P0191
- Fuel Rail Pressure (FRP) Sensor Performance
Diagnostic Fault Information
Circuit/System Description
The fuel rail pressure (FRP) sensor detects fuel pressure within the fuel rail. The engine control module (ECM) provides a 5 V reference voltage on the 5 V reference circuit and ground on the low reference circuit. The ECM receives a varying signal voltage on the signal circuit. The ECM monitors the voltage on the FRP sensor circuits. When the fuel pressure is high, the signal voltage is high. When the fuel pressure is low, the signal voltage is low.
Conditions for Running the DTC
Condition 1
* The engine speed is greater than 25 RPM for greater than 31 seconds.
* DTC P0191 runs once an ignition cycle at engine start up when the condition has been met.
Condition 2 and 3
* The engine speed greater than 25 RPM for greater than 30 seconds.
* The engine coolant temperature (ECT) at the previous engine shut down was warmer than 72°C (162°F).
* The ECT at engine start is colder than 55°C (131°F).
* At engine start, if the ECT is warmer than the intake air temperature (IAT), then the IAT must be within 35°C (63°F) of the ECT.
* At engine start, if the IAT is warmer than the ECT, then the ECT must be within 10°C (18°F) of the IAT.
* The block heater, if equipped, is not active.
* The engine off time since the previous engine shut down is greater than 4.2 hours.
* DTC P0191 runs once an ignition cycle at engine start up when the above conditions have been met.
Conditions for Setting the DTC
Condition 1
DTC P0087, P2187, or P2188 is set, and the fuel pressure at ignition ON is less than 120 kPa (17.4 psi) for greater than 4 seconds or for a cumulative of 30 seconds.
Condition 2
DTC P0088, P2177, or P2187 is set, and the fuel pressure at ignition ON is greater than 1500 kPa (218 psi) for greater than 4 seconds or for a cumulative of 30 seconds.
Condition 3
The fuel pressure at ignition ON is greater than 1500 kPa (218 psi) and a fuel pressure increase of greater than 385 kPa (56 psi) occurs during the fuel pump prime. The condition exists for greater than 4 seconds or for a cumulative of 30 seconds.
Action Taken When the DTC Sets
* DTC P0191 is a Type A DTC.
* A message center or an indicator may display Reduced Engine Power.
Conditions for Clearing the DTC
DTC P0191 is a Type A DTC.
Diagnostic Aids
A condition with the fuel tank module or the fuel pump control module (FPCM) may set this DTC.
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. Observe the scan tool DTC information, verify DTC P0627, P0628, P0629, P069E or U0109 is not set.
• If any of the DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle (Diagnostic Trouble Code (DTC) List - Vehicle).
2. Engine idling, observe the scan tool Fuel Rail Pressure Sensor parameter. The pressure should be approximately 3.5-5.5 Mpa (508-798 psi).
3. Engine idling, the scan tool Fuel Rail Pressure Sensor should be close to the scan tool Desired Fuel Rail Pressure. As the engine speed increases, the Desired Fuel Rail Pressure and the Fuel Rail Pressure Sensor should closely match each other.
4. Move related harnesses/connectors of the FRP sensor and verify the engine does not stumble, stall, or change engine speed.
• If the engine stumbles, stalls, or changes engine speed, test or repair the suspected harness or connection.
5. Observe the DTC information with a scan tool, DTC P0191 should not set.
6. 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
1. Ignition OFF, disconnect the multi-way harness connector X161 at the rear of the intake manifold.
2. Remove the fuse that supplies B+ to terminal 56-X2 of the K20 ECM.
Note: Testing for steps 3 through 7 is performed on the ECM side of the multi-way harness connector.
3. Ignition OFF, test for less than 5 ohm between the low reference circuit terminal 5 and ground.
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 ECM.
4. Install the fuse that supplies B+ to terminal 56-X2 of the K20 ECM.
5. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 11 and ground.
• If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
• If greater than the specified range, test the 5 V reference circuit for a short to voltage. If the circuit tests normal, replace the K20 ECM.
6. Ignition ON, verify the scan tool Fuel Rail Pressure Sensor voltage parameter is greater than 4.96 V.
• If less than the specified value, test the signal circuit terminal 12 for a short to ground. If the circuit tests normal, replace the ECM.
7. Connect a 3 A fused jumper wire between the signal circuit terminal 12 and the low reference circuit terminal 5. Verify the scan tool Fuel Rail Pressure Sensor voltage parameter transitions from greater than 4.96 V to less than 0.02 V.
• If the parameter does not transition from the maximum to minimum value, test the signal circuit for an open/high resistance or a short to voltage. If the circuit tests normal, replace the K20 ECM.
8. Ignition OFF, remove the intake manifold.
9. Connect the multi-way harness connector X161.
Note: Testing for steps 12 through 16 are performed at the FRP sensor connector.
10. Disconnect the B47 FRP sensor connector.
11. Remove the fuse that supplies B+ to terminal 56-X2 of the K20 ECM.
12. Ignition OFF, test for less than 5 ohm between the low reference circuit terminal 1 and ground.
• If greater than the specified range, test the low reference circuit for an open/high resistance.
13. Install the fuse that supplies B+ to terminal 56-X2 of the K20 ECM.
14. Ignition ON, test for 4.8-5.2 V between the 5 V reference circuit terminal 3 and ground.
• If less than the specified range, test the 5 V reference circuit for a short to ground or an open/high resistance.
• If greater than the specified range, test the 5 V reference circuit for a short to voltage.
15. Ignition ON, verify the scan tool Fuel Rail Pressure Sensor voltage parameter is greater than 4.96 V.
• If less than the specified value, test the signal circuit terminal 2 for a short to ground.
16. Connect a 3 A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the scan tool Fuel Rail Pressure Sensor voltage parameter transitions from greater than 4.96 V to less than 0.02 V.
• If the parameter does not transition from the maximum to the minimum value, test the signal circuit for an open/high resistance or a short to voltage.
17. If all circuits test normal, replace the B47 FRP sensor.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Fuel Pressure Sensor Replacement - Fuel Injection Fuel Rail (Fuel Pressure Sensor Replacement - Fuel Injection Fuel Rail)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming