Circuit Description
The fuel tank pressure (FTP) sensor measures the difference between the air pressure or vacuum in the evaporative emission (EVAP) system, and the outside air pressure. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal circuit voltage varies depending on EVAP system pressure or vacuum. If the FTP sensor signal voltage increases above a calibrated value, this DTC sets.
The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.
FTP Sensor Signal Voltage | Fuel Tank Pressure |
|---|---|
High, Approximately 1.5 Volts or More | Negative Pressure/Vacuum |
Low, Approximately 1.5 Volts or Less | Positive Pressure |
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 present for greater than 5 seconds. |
Action Taken When the DTC Sets
| • | The control module will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test ran and failed. |
| • | The control module will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The control module will turn OFF the MIL during the third consecutive trip in which the diagnostic ran and passed. |
| • | The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Test Description
The number below refers to the step number on the diagnostic table.
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 or P1639 fail this ignition? | -- | Go to DTC P1639 | 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 is greater than the specified value? | 4.3 V | Go to Step 6 | Go to Step 7 |
6 | Test the FTP signal circuit for a short to voltage or a short to a 5-volt reference circuit. Refer to Testing for a Short to Voltage and 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 Troubleshooting with a Test Lamp in Wiring Systems. Did the test lamp illuminate? | -- | Go to Step 9 | Go to Step 8 |
8 | Test the low reference circuit of the FTP sensor for an open. Refer to Testing for Continuity and 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 harness connector of the FTP sensor . 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 11 |
10 | Inspect for poor connections at the harness connector of the control module. 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 control module. 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 | |
