Circuit Description
The fuel tank pressure (FTP) sensor is a pressure transducer. The powertrain control module (PCM) supplies 5 volts to the FTP reference voltage circuit. The PCM also supplies a low reference and signal circuit to the FTP sensor. The PCM monitors the FTP sensor voltage and communicates the compressed natural gas (CNG) fuel level to the instrument panel. This DTC sets when the FTP pressure has not dropped during vehicle operation.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P1431 Fuel Pressure Sensor Performance
Conditions for Running the DTC
| • | The engine is operating on alternative fuel. |
| • | The vehicle has been driven a certain distance. |
Conditions for Setting the DTC
The CNG fuel tank pressure has not dropped during vehicle operation.
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. |
Diagnostic Aids
For an intermittent condition, refer to Intermittent Conditions .
Step | Action | Values | 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) |
2 |
Important: Other DTCs may set. Does the scan tool indicate that the FTP is more than the specified value? | 0 V | Go to Step 8 | Go to Step 3 |
3 | Measure the voltage from the 5-volt reference circuit with a DMM. Is the voltage near the specified value? | 5 V | Go to Step 4 | Go to Step 7 |
4 |
Does the scan tool indicate that the FTP is more than the specified value? | 4.7 V | Go to Step 5 | Go to Step 6 |
5 | Connect a test lamp between the sensor ground circuit and B+. Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 11 |
6 | Test the signal circuit of the FTP sensor for an open circuit or for high 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 14 | Go to Step 10 |
7 | Test the 5-volt reference circuit of the FTP sensor for an open circuit or for high 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 14 | Go to Step 10 |
8 | Test the signal circuit of the FTP sensor for a short to voltage. 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 14 | Go to Step 13 |
9 | Test for an intermittent and for a poor connection at the FTP sensor. 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 14 | Go to Step 12 |
10 | Test for an intermittent and for a poor connection at the power control module (PCM). 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 14 | Go to Step 13 |
11 | Repair the ground circuit of the FTP sensor for an open circuit or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems in the G/H Van Service Manual. Did you complete the repair? | Go to Step 14 | -- | |
12 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 14 | -- |
13 | Replace the PCM. Refer to Powertrain Control Module Replacement in the G/H Van Service Manual. Did you complete the replacement? | -- | Go to Step 14 | -- |
14 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 |
15 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
