Enhanced EVAP Gross Leak
The EVAP system prevents excess vacuum and vapor buildup in a sealed fuel tank system. An enhanced EVAP system is implemented on today's vehicles and a basic EVAP found on older model vehicles. A big difference is the ability of the enhanced system to monitor it's operation. The vehicle will run a vacuum or a pressure test depending on the model and inform the PCM of any leak greater than 0.020 in. (0.5 mm). Certain criteria (the drive cycle) must be met for the test to run and the large leak test is always run before the small leak test.
A P0457 gross leak detected code is often the result of the vehicle operators not tightening the refueling cap correctly after refueling. The same is true for the P0455 large leak code. Please note that a loose gas cap is not the only possible cause, but it is certainly the most likely. It could also be a cracked or loose hose, faulty gas tank seams, or anything else that may cause a large leak in the sealed EVAP system. A thorough visual inspection will often reveal loose hoses and lines.
The PCM will run a large leak test when it receives a signal from the fuel level sensor indicating an increase in fuel level (after refueling). If the fuel filler cap were left loose or worse off the fill tube, the PCM would set a pending code and illuminate the MIL in an attempt to warn the driver of the situation.
P0441: Incorrect purge flow (PURGE VALVE LEAK)
P0442: Small leak
P0443: Purge solenoid electrical fault
P0446: Blocked canister vent (HIGH SYSTEM VACUUM)
P0449: Canister vent solenoid electrical fault
P0452: Tank pressure sensor voltage (LOW)
P0453: Tank pressure sensor voltage (HIGH)
P0454: Tank pressure sensor voltage (NOISY)
P0455: LARGE LEAK (LOW SYSTEM VACUUM)
P0456: Very small leak
P0457: GROSS LEAK (CAP OFF)
P0460: Fuel level circuit
P0461: Fuel level sensor (STUCK/NOISY)
P0462: Fuel level sensor (VOLTAGE LOW)
P0463: Fuel level sensor (VOLTAGE HIGH)
P0464: Fuel level sensor (VOLTAGE NOISY AT IDLE)
Evaporative emissions were installed on vehicles in the late 1960's when they realized that up to 20% of the vehicles HC emissions occurred while the vehicle was in the driveway. The basic system installed on early model vehicles were vacuum controlled. The enhanced EVAP system found on today's vehicles is more complex, far superior, and PCM controlled. There are different systems found on different model vehicles. Always check for TSB's and refer to the manual for any manufacturer specific testing procedures.
