For 1990-2009 cars

## DTC P0191 ECM DTC

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### 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 reference ground 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 30 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 block heater, if equipped, is not active.

• | The engine coolant temperature (ECT) at the previous engine shut down was greater than 72°C (162°F).

• | The ECT at engine start-up is less than 55°C (131°F).

• | At engine start, if the ECT is greater 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 greater than the ECT, then the ECT must be within 10°C (18°F) of the IAT.

• | 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 time 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 time 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 350 kPa (51 psi) occurs during the fuel pump prime. The condition exists for greater than 4 seconds or for a cumulative time 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 primary fuel tank module or the fuel pump relay 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

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### 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, and P069E is not set.

⇒ | If a DTC is set, refer to DTC P069E for further diagnosis.

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 X161 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 X161 at the rear of the intake manifold.
10. Disconnect the FRP sensor connector.
11. Remove the fuse that supplies B+ to terminal 56 X2 of the ECM.

Note: Testing for steps 11 through 15 are performed at the FRP sensor connector.

12. Ignition OFF, test for less than 5 Ω 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.

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 for a short to ground.

16. Connect a 3 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. 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.

• | Fuel Pressure Sensor Replacement - Fuel Injection Fuel Rail

• | Control Module References for ECM replacement, setup, and programming