DTC P0191 w/o JL4
Circuit Description
The fuel rail pressure (FRP) sensor is a pressure sensor. The fuel injector control module (FICM) supplies about 5 volts on the FRP sensor reference voltage circuit. The FICM 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 FICM monitors the FRP sensor voltage and communicates the data to the powertrain control module (PCM) by a dedicated pulse width modulated (PWM) circuit.
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
| • | The CNG fuel tank pressure is more than 5,171 kPa (750 psi). |
| • | The ECT is more than 20°C (68°F). |
| • | The engine speed is more than 600 RPM. |
| • | The mass air flow (MAF) is less than 175 g/s. |
Conditions for Setting the DTC
| • | The FRP sensor is less than 827 kPa (120 psi), or more than 1517 kPa (220 psi). |
| • | The condition exists for at least 5 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the 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
The numbers below refer to the step numbers on the diagnostic table.
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This step determines if the condition is present.
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This step determines if the low pressure lock-off (LPL) solenoid is functioning.
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The step tests the low reference circuit of the FRP sensor.
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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.
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This step test the signal circuit of the FRP sensor.
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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.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check Alternative Fuels - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Alternative Fuels (Engine Controls) |
Does the scan tool display the FRP sensor pressure within the specified range? | 827-1,517 kPa (120-220 psi) | Go to Step 3 | Go to Step 4 | |
3 |
Does the DTC fail this ignition cycle? | -- | Go to Step 4 | Go to Intermittent Conditions |
Does the LPL operate as commanded? | -- | Go to Step 5 | ||
Does the test lamp illuminate? | -- | Go to Step 6 | Go to Step 10 | |
Is the voltage at the specified value? | 5.00 V | Go to Step 7 | Go to Step 11 | |
Does the scan tool display the FRP sensor voltage more than the specified value? | 4.95 V | Go to Step 8 | Go to Step 9 | |
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Important: Return to this diagnostic procedure, after performing the Fuel System Diagnosis. Perform the Fuel System Diagnosis procedure. Refer to Fuel System Diagnosis . Did find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | |
9 | Test the signal circuit of the FRP sensor for an open or excessive resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
10 | Test the low reference circuit of the FRP sensor for excessive resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
11 | Test the 5-volt reference circuit of the FRP sensor for excessive resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 |
12 | Inspect for proper terminal contact at the harness connector of the fuel injector control module (FICM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems in the G/H Van Service Manual. Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 |
13 | Replace the FRP sensor. Refer to Fuel Injection Fuel Rail Fuel Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- |
14 | Replace the FICM. Refer to Fuel Injector Control Module Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- |
15 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 16 |
16 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
