Circuit/System Description

The EVAP leak detection pump assembly consists of three main components - a vacuum pump, a switching valve, and a pressure sensor. This DTC deals with the pressure sensor within the leak detection pump.

This diagnostic is executed when propulsion is active, engine ON or OFF, purge is not enabled, and the vent valve is closed or open. The diagnostic does not run when purge is enabled because it can influence the EVAP leak detection pump pressure sensor reading if there is any restriction in the fresh air plumbing.

This diagnostic is disabled when the Fuel Tank Pressure (FTP) Sensor Circuit Performance Diagnostic P0451 or the EVAP System Low Purge Flow Diagnostic P0497 is currently running.

The EVAP leak detection pump pressure sensor performs a correlation to barometric pressure (BARO). After a short delay period, the EVAP leak detection pump pressure sensor, absolute, reading is compared to the BARO based on the MAP sensor. Large deviations will increment the fail counter. When the fail count threshold is exceeded, then P1458 is set. There are two different threshold calibrations used in the comparison to the BARO. A smaller threshold is used when there has been a recent BARO update and then a larger threshold value is used when there has not been.