P0191

DTC P0191

CIRCUIT DESCRIPTION
The fuel rail pressure (FRP) sensor is a pressure sensor. The powertrain control module (PCM) supplies about 5 volts on the FRP sensor reference voltage circuit. The PCM also supplies a ground circuit and a signal circuit to the FRP sensor. When the fuel rail pressure is normal, the FRP signal voltage rises to near 2.5 volts. If the fuel rail pressure increases, the FRP signal voltage increases. The PCM uses the FRP sensor data in order to adjust fuel trim.

This DTC sets when the FRP sensor signal voltage is outside of the normal operating range of the sensor.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0191 Fuel Rail Pressure Sensor Performance

CONDITIONS FOR RUNNING THE DTC
- DTCs P0005, P0192, P0193, P0336, P1207, P1432, P1433, or P2665 are not set.
- The compressed natural gas (CNG) fuel tank pressure (FTP) is more than 1723 kPa (250 psi).
- The engine coolant temperature (ECT) is more than 20°C (68°F).
- The engine speed is more than 100 RPM.
- The mass air flow (MAF) is less than 200 g/s.

CONDITIONS FOR SETTING THE DTC
- The FRP sensor is less than 206 kPa (30 psi), or more than 620 kPa (90 psi).
- The condition exists for at least 3 seconds.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
- The control module switches over to gasoline fuel operation.
- The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

TEST DESCRIPTION

Step 1 - Step 9:

Step 10 - Step 16:

The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if the condition is present.
4. This step determines if the low pressure lock-off (LPL) solenoid is functioning.
5. This step tests the low reference circuit of the FRP sensor.
6. This step determines if the 5-volt reference circuit is the cause of the condition. The DMM should display 5.0 volts across the test lamp.
7. This step tests the signal circuit of the FRP sensor.
9. This step verifies that a mechanical fuel system condition is not the cause of the concern. A fuel pressure regulator condition may cause this DTC to set.