Circuit Description
The powertrain control module (PCM) provides monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the enhanced evaporative emission (EVAP) diagnostic. The PCM supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases when the fuel tank pressure decreases. A negative pressure or vacuum indicates high voltage. The FTP sensor signal voltage decreases when the fuel tank pressure increases. A positive pressure indicates low voltage. This diagnostic trouble code (DTC) sets when the FTP sensor signal goes above a predetermined value.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The fuel tank pressure sensor voltage is more than 4.9 volts. |
| • | All conditions are present for more than 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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If DTC P1635 and P1639 set, the 5-volt reference circuit is shorted to a voltage.
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The FTP sensor signal circuit is routed through connector C152. This may provide a good test point for diagnosing concerns with this circuit.
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The FTP sensor low reference circuit is routed through connector C152. This may provide a good test point for diagnosing concerns with this circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
Did DTC P1635 and P1639 fail this ignition? | -- | Go to DTC P1635 | Go to Step 3 | |
3 |
Is the FTP sensor voltage more than the specified value? | 4.3 V | Go to Step 5 | Go to Step 4 |
4 |
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions |
5 |
Does the scan tool indicate that the FTP sensor voltage parameter is greater than the specified value? | 1.0 V | Go to Step 6 | Go to Step 7 |
Test the signal circuit of the FTP for a short to voltage, or for a short to a voltage reference circuit. Refer to Circuit Testing or Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 | |
7 | Probe the low reference circuit of the FTP sensor with a test lamp connected to battery voltage. Refer to Probing Electrical Connectors in Wiring Systems. Did the test lamp illuminate? | 0 V | Go to Step 9 | Go to Step 8 |
Test the low reference circuit of the FTP sensor for an open. Refer to Using Connector Test Adapters or Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 | |
9 | Inspect for poor connections at the FTP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections or Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
10 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
11 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Does the DTC run and pass? | -- | Go to Step 14 | Go to Step 2 |
14 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
