Circuit Description

The Powertrain Control Module (PCM) uses input from fuel level sensor to calculate expected vapor pressures within fuel system. Vapor pressures vary as fuel level changes. Vapor pressure is critical to determining if EVAP control system is operating properly. Fuel level information is used in determining whether to run an EVAP control system diagnostic. A fuel level that is too high or too low may prevent EVAP control system diagnostics from accurately detecting a fault.

When DTC sets, MIL will illuminate after 2 consecutive ignition cycles in which diagnostic runs with active fault. PCM will record operating conditions at time of failure and store information in FREEZE FRAME/FAILURE RECORDS data buffer.