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 goes below a calibrated value, this DTC sets.
The following table illustrates the relationship between the 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 ignition is ON.
Conditions for Setting the DTC
| • | The fuel tank pressure (FTP) sensor voltage is less than 0.1 volts |
| • | All conditions 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 number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
2 |
Did DTC P1639 fail this ignition? | -- | Go to Step 3 | |||||||
3 | Observe the Fuel Tank Pressure sensor parameter with a scan tool. Is the Fuel Tank Pressure sensor parameter less than the specified value? | 0.1 V | Go to Step 5 | Go to Step 4 | ||||||
4 |
Did the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | ||||||
Is the Fuel Tank Pressure sensor parameter within the specified value? | 4.9-5.1 V | Go to Step 8 | Go to Step 6 | |||||||
6 | Test the 5-volt reference circuit for an open circuit or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 7 | ||||||
7 | Test the signal circuit for the following conditions:
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 9 | ||||||
8 | Test for an intermittent and for a poor connection at 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 12 | Go to Step 10 | ||||||
9 | Test for an intermittent and for a poor connection at 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 12 | Go to Step 11 | ||||||
10 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
11 | Replace the control module. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 12 | -- | ||||||
12 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 13 | ||||||
13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||||
