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, EVAP vent solenoid,
and the EVAP purge solenoid. 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 vacuum to the system and monitoring pressure decay. The ECM
monitors the vacuum level through the fuel tank pressure sensor. In the fourth 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 purge solenoid is turned Off, sealing the system.
If a sufficient vacuum cannot be achieved, a large leak fault is detected.
DTC Parameters
DTC P0455 will set when:
| • | Vehicle speed not present |
| • | Fuel system is in closed loop |
| • | Engine Temperature at start is between -8.25°C - 75°C (17°F -
167°F) |
| • | IAT is between -8.25°C - 50.25°C (17°F - 122°F) |
| • | Battery voltage greater than 11.1 volts |
| • | Engine run time greater than 1 minute and 45 seconds |
| • | Altitude less than 9000 ft |
| • | Fuel Level between 1.85 and 1 gal |
| • | Sufficient vacuum cannot be achieved |
| • | No TP, ECT, VSS, fuel tank pressure, oxygen sensors, idle control purge
valve, vent valve, battery voltage, misfire, or EGR code set |
P0455 is a (type B) DTC.
Diagnostic Aids
The following could result in a large leak:
| • | Missing, improperly installed (loose) or faulty fuel cap. |
| • | Disconnected or damaged EVAP vent hose. |
| • | Disconnected, damaged, pinched or blocked fuel tank vapor lines. |
| • | Damaged or leaking EVAP canister. |
| • | Leaking fuel sender assembly or O-ring. |
| • | Leaking fuel tank or filler neck. |
| • | Stuck open EVAP purge solenoid. |
