EVAP System Diagnostics

The PCM monitors the following EVAP system electrical components for low and high voltage faults.
^ Fuel tank pressure sensor
^ EVAP purge solenoid
^ EVAP vent solenoid

As part of the On-board diagnostics second generation (OBD II) requirements, the government mandates that all automobile manufactures detect a 0.040 inch or greater diameter leak in the EVAP system (for 2001, the PCM will detect a 0.020 in leak). To comply, the PCM monitors the EVAP system for large and small leaks and whether the EVAP purge and vent solenoid valves are stuck closed or open.

IMPORTANT: The following flowchart consists of a series of tests run by the PCM which describes the entire EVAP DIAGNOSTIC TEST. Each step the PCM performs is dependent on the accuracy of the fuel tank pressure sensor. The FUEL TANK PRESS. SENSOR reading on Scan tool with ignition On, engine Off and fuel cap removed should read between 1.3 and 1.7 volts.

The EVAP SERVICE BAY TEST on the Scan tool is nearly identical to the following On-board test. Performing the EVAP SERVICE BAY TEST simply forces the PCM to run the On-board test regardless if operating conditions have been met.