Circuit Description
The control module 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 control module supplies a 5-volt reference and ground to the sensor. The FTP sensor signal voltage increases as the FTP decreases. Negative pressure or vacuum equals high voltage. The FTP sensor signal voltage decreases as the fuel tank pressure increases. Positive pressure equals low voltage. When the FTP sensor signal goes below a predetermined value, DTC P0452 will set.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
| • | The FTP sensor voltage is less than 0.1 volt |
| • | 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 numbers below refer to the step numbers on the diagnostic table.
-
If DTC P1639 sets, the 5-volt reference may be shorted to ground.
-
If the FTP sensor voltage is near 5 volts, the FTP sensor signal and 5-volt reference circuits are OK from the fuel tank harness connector to the control module.
Step | Action | Value(s) | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||||||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |||||||
Did DTC P1639 fail this ignition? | -- | Go to DTC P1639 | Go to Step 3 | |||||||
3 | Does the scan tool indicate that the FTP sensor voltage is less than the specified value? | 0.1 V | Go to Step 5 | Go to Step 4 | ||||||
4 |
Does the DTC fail this ignition? | -- | Go to Step 5 | Go to Intermittent Conditions | ||||||
Does the scan tool indicate that the FTP sensor voltage is near the specified value? | 5.0 V | Go to Step 8 | Go to Step 6 | |||||||
6 | Test the 5-volt reference circuit of the FTP sensor for an open, between the body pass through connector and the control module. 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 of the FTP sensor for a short to ground, or an open between the body pass through connector and the control module. 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 |
Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10 | ||||||
9 | 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 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 |
Does the DTC run and pass? | -- | Go to Step 13 | Go to Step 2 | ||||||
13 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |||||||
