Circuit Description
Once every drive cycle, the EVAP system runs a 25-40 second diagnostic
where it monitors possible leaks, the fuel tank pressure sensor, vent value and the
canister purge value. This diagnostic has 5 phases and can set
several different codes depending on which part of the diagnostic fails. The evaporative
emission system is tested by applying pressure (vacuum) to the system and monitoring
pressure decay. The ECM monitors the vacuum level through the fuel tank vapor pressure
sensor. In the fifth phase of the diagnostic, the EVAP vent solenoid is commanded
closed (normally open valve) and the EVAP canister purge valve is commanded to a fixed
duty cycle, allowing the engine to draw a vacuum on the entire evaporative emission
system. After a calibrated vacuum level is achieved, the EVAP canister purge valve
is turned Off, sealing the system. A leak is detected by monitoring for a decrease
in vacuum level over a calibrated period of time, while keeping all other variables
constant.
DTC Parameters
DTC P0442 will set when:
| • | Vehicle speed not present |
| • | Fuel System in closed loop |
| • | Engine Temperature is between -8.25°C (17°F) and 50.25°C (122°F) |
| • | Battery voltage greater than 11.1 volts |
| • | Engine run time greater than 17 minutes |
| | NOTE: Under some operating conditions, this diagnostic may run before a full
17 minutes have expired. |
| • | Altitude less than 9000 ft. |
| • | Fuel level between 1.85 and 14 gal. |
| • | No TP, ECT, VSS, tank pressure, oxygen sensors, idle control, purge valve,
vent valve, battery voltage, misfire, and EGR codes set. |
P0442 is a (type B) DTC.
Diagnostic Aids
The following conditions could result in a small leak:
| • | Missing or leaking O-rings at fuel vapor line. |
| • | Cracked or damaged EVAP Canister. |
| • | Damaged source vacuum line, EVAP purge line, EVAP vent hose or fuel tank
vapor line. |
| • | EVAP vent solenoid stuck open. |
| • | EVAP service port valve leak. |
