For 1990-2009 cars

### Circuit Description

The evaporative emission (EVAP) system is used to store fuel vapors as to reduce the amount of unburned fuel from escaping into the atmosphere. The EVAP system consists of the EVAP canister, fuel tank pressure (FTP) sensor, EVAP lines and hoses, EVAP purge solenoid - normally closed, EVAP service port, EVAP vent solenoid - normally open, and the fuel tank. The engine control module (ECM) monitors the EVAP system for circuit faults in the EVAP purge solenoid, EVAP vent solenoid, and FTP sensor circuits. The ECM also monitors the EVAP system for leaks, between the EVAP vent and EVAP purge solenoid. When certain conditions have been met, the ECM will perform an EVAP diagnostic test at idle with no vehicle speed, which will require a 5 consecutive phase A, B, C, D, and E test. DTC P0496 will set if too much vacuum is present during Phase B or Phase E of the EVAP diagnostic system test indicating continuous purge flow.

### Conditions for Setting the DTC

DTC P0496 will sets if the fuel tank pressure indicates less than 2.37 volts less, than -1.21 mm Hg (-0.65 in H2O) during Phase B of the EVAP diagnostic system test or less than 1.24 volts, less than -11.25 mm Hg (-6.02 in H2O) during Phase E of the EVAP diagnostic test indicating continuous purge flow when:

• | The condition exists anytime during Phase B, for 4 seconds, or anytime during Phase E, for 10.5 seconds.

• | The EVAP purge solenoid is commanded OFF.

• | The EVAP vent solenoid is commanded ON.

• | The engine is at idle.

• | The vehicle speed is 0 mph.

• | The engine load is less than 35 percent.

• | The MAP is less than 40 kPa.

• | The battery voltage is greater than 11 volts.

• | The startup ECT is between 8-75°C (46-167°F).

• | The IAT is between 8-50°C (46-122°F).

• | The long term fuel trim cells are learned. If not learned, the engine must run longer than 16 minutes and 45 seconds.

• | The fuel level is between 6-48 L (1.6-12.7 gallons).

• | No ECT, EVAP purge solenoid, EVAP vent solenoid, fuel tank pressure, idle speed, HO2S, throttle actuator, TP sensor, or vehicle speed DTCs have been set.

DTC P0496 diagnostic runs once during Phase B and Phase E of the EVAP diagnostic test once per ignition cycle.

If an EVAP diagnostic test is aborted due to a changing enable criteria, the ECM will attempt to rerun the EVAP diagnostic test up to 3 times per ignition cycle.

DTC P0440 is a type B DTC.

### Diagnostic Aids

Important:

• | If any EVAP system DTC is set, EVAP special functions on the scan tool will not be allowed. Clear the DTCs before performing these tests.

• | The ECM uses the fuel tank pressure sensor to detect the vapor in the fuel tank during all parts of the EVAP diagnostic system test. Make sure the fuel tank pressure sensor is not skewed by verifying FUEL TANK PRESS. SENSOR on the scan tool is between 2.35-2.85 volts with the ignition ON and the engine OFF and the fuel cap removed.

The most likely cause of DTC P0440 is a stuck open EVAP purge solenoid. Use the scan tool to command EVAP PURGE SOLENOID ON at 70 percent duty cycle. The solenoid should click at an even rate. Replace the solenoid if the solenoid intermittently sticks.

Refer to EVAP System Description at the end of this section for a complete EVAP diagnostic test description.