Circuit/System Description
The fuel tank pressure (FTP) sensor measures air pressure or vacuum in the evaporative emission (EVAP) system. The engine control module
(ECM) supplies a 5-volt reference and a low reference circuit to the FTP sensor. The FTP sensor signal voltage varies depending on EVAP system
pressure or vacuum. The controller also uses this FTP signal to determine atmospheric pressure for use in the engine-off small leak test, DTC
P0442. Before using this signal as an atmospheric reference it must first be re-zeroed.
Conditions for Running the DTC
P0451
* DTC P0451 runs only when the engine-off natural vacuum small leak test, P0442, executes.
* The number of times this test runs can range from 0-2 per engine-off period. The length of the test can be up to 10 minutes.
P0452 and P0453
DTC P0452 and P0453 run continuously when the ignition is ON.
P0454
* DTC P0454 runs only when the engine-off natural vacuum small leak test, P0442, executes.
* This test can run once per engine-off period. The length of the test can be up to 10 minutes.
* A refueling event is not detected.
Conditions for Setting the DTC
P0451
This DTC will set if the controller is unable to re-zero the FTP sensor voltage within a calibrated range during the engine-off small leak test, P0442.
P0452
The FTP sensor voltage is less than 0.1 volt for more than 5 seconds.
P0453
The FTP sensor voltage is more than 4.9 volts for more than 5 seconds.
P0454
If, during the engine-off natural vacuum small leak test, P0442, the ECM detects an abrupt FTP signal change, other than a refueling event, this
DTC will set. An abrupt change is defined as a change of 0.45 inch H2O in the span of 1 second.
Action Taken When the DTC Sets
* DTC P0451 and P0454 are Type A DTCs.
* DTC P0452 and P0453 are Type B DTCs.
Conditions for Clearing the MIL/DTC
* DTC P0451 and P0454 are Type A DTCs.
* DTC P0452 and P0453 are Type B DTCs.
Diagnostic Aids
P0451 and P0454
* A restriction in the EVAP canister or vent lines could prevent fuel vapor pressure from bleeding off fast enough. If the vent system cannot
bleed off pressure fast enough, the re-zero procedure may not complete successfully, which could cause this code to set.
* Ensure that the reference port on the FTP sensor is unobstructed.
* An FTP sensor that is skewed or does not have a linear transition from low to high may cause this code to set. Scan tool output controls,
snapshot, and plot functions can help detect erratic sensor response. To test the sensor signal under vacuum conditions, use the Quick
Snapshot and the Purge/Seal functions to capture data while commanding purge to 20 percent, then plot the data to look for erratic sensor
