DTC P0191 ECM

Diagnostic Instructions

DTC Descriptors

DTC P0191: Fuel Rail Pressure (FRP) Sensor Performance

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
5 V Reference Voltage	P0193, P0642	P0193	P0193, P0643	P0191
FRP Sensor Signal	P0192	P0193	P0193	P0191
Low Reference	--	P0193	--	P0191

Circuit/System Description

The fuel rail pressure (FRP) sensor detects fuel pressure within the fuel rail. The engine control module (ECM) provides a 5-volt reference voltage on the 5-volt 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

Condition 2 and 3

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

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) will set this DTC.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References 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 either DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle.

2. Engine idling, observe the scan tool Actual Fuel Rail Pressure parameter. The pressure should be approximately 3.5-5.5 Mpa (508-798 psi).
3. Engine idling, the Actual Fuel Rail Pressure should be close to the Desired Fuel Rail Pressure. As the engine speed increases, the Desired Fuel Rail Pressure and the Actual Fuel Rail Pressure 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 X117 at the rear of the intake manifold.
2. Remove the fuse that supplies B+ to terminal 56-X2 of the 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 Ω 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 ECM.

4. Install the fuse that supplies B+ to terminal 56-X2 of the ECM.
5. Ignition ON, test for 4.8-5.2 V between the 5-volt reference circuit terminal 11 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

6. Ignition ON, verify the scan tool FRP 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 FRP 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 ECM.

8. Ignition OFF, remove the intake manifold.
9. Connect the multi-way harness connector X117.

Note:  Testing for steps 10 through 15 are performed at the FRP sensor connector.

10. Disconnect the FRP sensor connector.
11. Remove the fuse that supplies B+ to terminal 56-X2 of the ECM.
12. Ignition OFF, test for less than 5 Ω 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 ECM.
14. Ignition ON, test for 4.8-5.2 V between the 5-volt reference circuit terminal 3 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

15. Ignition ON, verify the scan tool FRP 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 FRP 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 FRP sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

DTC P0191 FPCM

Diagnostic Instructions

DTC Descriptor

DTC P0191: Fuel Rail Pressure (FRP) Sensor Performance

Diagnostic Fault Information

Circuit	Short to Ground	Open or High Resistance	Short to Voltage	Signal Performance
5-Volt Reference	P0641	P0641, P06A6	P0641	P06A6
Fuel Rail Pressure (FRP) Sensor Signal	P0192	P0191, P0192	P0193	P0191
Fuel Line Pressure Sensor Low Reference	--	P0641, P06A6	--	P06A6

Circuit/System Description

The fuel pressure sensor is mounted on the fuel line. Fuel pressure is measured by the fuel pressure sensor. The fuel pump flow control module (FPCM) monitors the voltage signal from the fuel pressure sensor and also supplies the voltage and the ground of the fuel pressure sensor.

Conditions for Running the DTC

Conditions for Setting the DTC

The FPCM does not detect a change in the fuel rail pressure (FRP) of at least 30 kPa (4.4 psi) when the fuel pump is operating at its minimum or maximum voltage limits for over 5 seconds.

Action Taken When the DTC Sets

DTC P0191 is an A type DTC.

Conditions for Clearing the DTC

DTC P0191 is an A type DTC.

Diagnostic Aids

Using the Failure Records data may help locate an intermittent condition. If you cannot duplicate the DTC, the information in the Failure Records can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can help determine how many ignition cycles that the diagnostic test reported a pass and/or a fail.

Reference Information

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Fuel System Description

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

Important: Verify that the fuel tank is not empty. Only perform this diagnostic if there is at least 2 gallons of fuel in the fuel tank. Clear the DTC, and start and run the engine. Verify that the DTC P0191 resets before proceeding with the circuit system testing. If the DTC does not reset, refer to diagnostic aids.

1. Ignition OFF, disconnect the harness connector at the fuel line pressure sensor.
2. Ignition OFF, test for less than 1.0 ohm between the low reference circuit terminal 2 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 FPCM.

3. Ignition ON, test for 4.8-5.2 volts between the fuel line pressure sensor 5-volt reference circuit terminal 3 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the FPCM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the FPCM.

4. Ignition ON, observe the Fuel Pump Control Module Fuel Rail Pressure Sensor parameter.
5. Install a 3A fused jumper wire between the 5-volt reference circuit terminal 3 and the fuel line pressure sensor signal circuit terminal 1. The scan tool should display between 4.8-5.2 volts.

⇒	If less than the specified range, test the signal circuit terminal 1 for a short to ground or an open/high resistance. If the circuit tests normal, replace the FPCM.

⇒	If greater than the specified range, test the signal circuit terminal 1 for a short to voltage. If the circuit tests normal, replace the FPCM.

6. If all circuits test normal, replace the fuel pressure sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.