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 ECM monitors the EVAP system for circuit faults
in the EVAP purge solenoid, EVAP vent solenoid, and FTP sensor circuits. The engine
control module (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 P0442 will set if vacuum decays too
quickly during Phase E of the EVAP diagnostic system test indicating a small
EVAP system leak.
Conditions for Setting the DTC
DTC P0442 will set if the vacuum decay is greater than 0.35 fuel
tank pressure sensor volts, changing from -6.00 mm Hg (-3.21 in H2O)
to higher than -3.00 mm Hg (-1.61 in H2O)
over a 10.5 second period during phase E of the EVAP diagnostic system
test indicating a small EVAP leak when:
| • | The condition exists for the entire phase E of 10.5 seconds. |
| • | The EVAP purge solenoid is commanded OFF. |
| • | The EVAP vent solenoid is commanded ON. |
| • | Vehicle speed is 0 mph. |
| • | Engine load is less than 35 percent. |
| • | The MAP is less than 40 kPa. |
| • | Battery voltage is greater than 11 volts. |
| • | Startup ECT is between 8-75°C (46-167°F). |
| • | The IAT is between 8-75°C (46-122°F). |
| • | 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 P0442 diagnostic runs once during Phase E of the EVAP diagnostic
system test once per ignition cycle.
If an EVAP diagnostic test is aborted due to changing enable criteria, the ECM
will attempt to rerun the entire EVAP diagnostic system test up to 3 times
per ignition cycle.
DTC P0442 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 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. |
Use the EVAP System Tester to locate the small leak. Follow the operating instructions
in the EVAP System Description at the end of this section.
Refer to EVAP System Description at the end of this section for a complete EVAP
diagnostic test description.
Possible cause of a small EVAP leak:
| • | EVAP vent solenoid valve not fully seating |
| • | EVAP service port valve leaking |
| • | EVAP line/hose connections leaking |
| • | Fuel sender O-ring leaking |
| • | Fuel tank pressure sensor seal leaking |
USE THE FOLLOWING EVAP SYSTEM PICTURE, WHICH WILL POINT TO POSSIBLE LEAK AREAS.
