Component Tests and General Diagnostics

The PCM tests the EVAP system by applying vacuum to a sealed system, then monitoring the rate of vacuum decay. The PCM determines the vacuum decay using the signal from the fuel tank pressure sensor. The PCM tests the EVAP system for the following conditions:
^ Large and small leaks-P0440 and P0442
^ Excess vacuum-P0446 Purge flow during non-commanded conditions-P1441
^ Fuel pressure sensor and-P0452, P0453
^ Fuel level sensor faults-P0461, P0462 and P0463
^ [1][2]EVAP purge (P0443), and vent valve (P0449) solenoid malfunctions

The PCM tests the EVAP system, when the following conditions are met:
^ No TP sensor, MAP sensor, VSS, IAT sensor, ECT sensor, HO2S sensor, fuel trim, fuel level sensor, misfire, fuel Injectors, EGR pintle position, fuel tank pressure sensor, fuel level sensor, or MAF sensor DTCs are set.
^ Battery voltage is between 10 and 18 volts.
^ Barometric pressure is more than 72 kPa.
^ Fuel level is steady between 15 and 85 percent.

At an appropriate time, the PCM turns ON the [1][2]EVAP purge and EVAP vent valves. This opens the EVAP purge valve and closes the EVAP vent valve. The engine draws a small vacuum on the entire EVAP system. After achieving the desired vacuum level, the PCM turns OFF the EVAP purge valve. The PCM detects a leak by monitoring decrease in the vacuum level over a period of time. A small leak in the system causes DTC P0442 to set. A large leak, EVAP or a malfunctioning purge valve will causes an insufficient vacuum level in the system and will set DTC P0440. A large leak may be the result of the following conditions:
^ Disconnected or malfunctioning fuel tank pressure sensor
^ Missing or malfunctioning fuel cap
^ Disconnected, damaged, pinched, or blocked [1][2]EVAP purge line
^ Disconnected or damaged [1][2]EVAP vent hose
^ Disconnected, damaged, pinched, or blocked fuel tank vapor line
^ Disconnected or malfunctioning [1][2]EVAP purge valve
^ Disconnected or malfunctioning EVAP vent valve
^ An open ignition feed circuit to the EVAP vent or purge valve
^ Damaged EVAP canister
^ Leaking fuel sender assembly O-ring
^ Leaking fuel tank or fuel filler neck

The PCM also tests the EVAP system for a restricted or blocked vent path. First, the PCM turns ON the [1][2]EVAP purge and EVAP vent valves. As indicated above, this opens the EVAP purge valve and closes the EVAP vent valve. The engine draws a small vacuum on the entire EVAP system. Then, at the appropriate vacuum level, the PCM turns OFF the EVAP purge and EVAP vent valves. This closes the EVAP purge valve and opens the EVAP vent valve. At this time, the PCM monitors the vacuum decay using the signal from the fuel tank pressure sensor. Unless a blocked vent path is present, the PCM should detect a quick decay of the vacuum. DTC P0446 will set if a blocked vent path is present. DTC P0446 may be the result of the following conditions:
^ Malfunctioning EVAP vent valve-stuck closed
^ Plugged, kinked, or pinched vent hose
^ Shorted EVAP vent valve control circuit

To check for a continuous purge condition, the PCM turns OFF the [1][2]EVAP purge valve and turns ON the EVAP vent valve. This closes the EVAP purge valve and opens the EVAP vent valve. The PCM again monitors the vacuum level in the EVAP system. With the purge valve closed and the vent valve opened, the PCM should detect no vacuum in the EVAP system unless a continuous purge conditions is present. DTC P1441 will set if the PCM detects a continuous purge condition. Any of the following conditions will set DTC P1441:
^ [1][2]EVAP purge valve leaking
^ [1][2]EVAP purge and engine vacuum source lines switched at the valve
^ [1][2]EVAP purge valve control circuit grounded