Evaporative Emission Control System Diagnosis

Diagnostic Chart (Part 1 Of 3):

Diagnostic Chart (Part 2 Of 3):

Diagnostic Chart (Part 3 Of 3):

CIRCUIT DESCRIPTION
The evaporative system includes the following components:
^ The fuel tank
^ The EVAP canister vent valve
^ The fuel pipes and hoses
^ The fuel can
^ The EVAP vapor lines
^ The EVAP purge lines
^ The evaporative emission canister
^ The EVAP purge valve

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 Fuel Level sensor faults (P0452, P0453, P0461, P0462, and P0463)
^ EVAP Purge and Vent Valve solenoid malfunctions (P0443 and P0449)

The PCM tests for a leak in the EVAP system by drawing a vacuum on the system, then watching the rate at which the vacuum decays. The PCM uses the input from the Fuel Tank Pressure sensor to determine the rate of vacuum decay. At the appropriate time, the PCM turns ON the EVAP purge and canister vent valves (purge valve opens, the vent valve closes). This seals the system, and allows the engine to draw a vacuum on the system. At a calibrated time or vacuum level, the PCM turns the purge valve OFF, and checks the system vacuum. If the system is unable to achieve the calibrated vacuum level, the PCM will set DTC P0440. The following conditions will set DTC P0440:
^ Disconnected or malfunctioning fuel tank pressure sensor (should set DTC P0453 or P0453)
^ Missing or malfunctioning fuel cap
^ Disconnected, damaged, pinched, or blocked EVAP purge line
^ Disconnected or damaged EVAP canister vent hose
^ Disconnected, damaged, pinched, or blocked fuel tank vapor line
^ Malfunctioning EVAP purge valve
^ Disconnected or malfunctioning EVAP canister vent valve
^ Open ignition feed circuit to the EVAP canister vent or purge valve (should set DTC P0443 or DTC P0449)
^ Damaged EVAP canister
^ Leaking fuel sender assembly O-ring
^ Leaking fuel tank or fuel filler neck

CONDITIONS FOR RUNNING THE DTC
^ No IAT sensor, MAP sensor, TP sensor, HO2S sensors VSS sensor or ECT sensor DTC's set.
^ DTC P0125 inactive.
^ System voltage is between 10 and 18 volts.
^ Barometric pressure is more than 72 kPa.
^ Fuel level sensor indicates that the fuel level is between 15 and 85 percent.
^ Engine coolant temperature less than 30°C.
^ Intake air temperature is between 4°C and 30°C.
^ BARO is greater than 72.5 kPa (8000 feet).
^ Start-up ECT and IAT are within 8°C of each other.

CONDITIONS FOR SETTING THE DTC
The EVAP system is unable to achieve or maintain the calibrated vacuum level.

ACTION TAKEN WHEN THE DTC SETS

IMPORTANT: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that the system has passed, or the code has been cleared, the diagnostic must fail during two consecutive trips before setting a DTC. The initial failure is not reported to the diagnostic manager or displayed on the scan tool.
^ The PCM will illuminate the Malfunction Indicator Lamp (MIL) after the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame and Fail Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn the MIL OFF after the third consecutive trip in which the diagnostic runs and passes.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using the scan tool Clear DTC Information function.

DIAGNOSTIC AIDS

IMPORTANT: An accurate indication of fuel level is required for the PCM to properly RUN this diagnostic. Always diagnose fuel level sensor DTC's before performing this diagnostic table. Always check for fuel level sensor DTC's stored as History.

Perform a physical inspection of the EVAP system. Check for the following conditions:
^ A loose, missing, defective, or incorrect fuel tank cap
^ Incorrectly routed, kinked, pinched, plugged, or defective EVAP system vacuum and vapor lines
^ A malfunctioning, or damaged EVAP vapor canister

Check for charcoal release from the EVAP vapor canister. Refer to the EVAP System Cleaning procedure.

If the condition is intermittent, refer to Intermittent Conditions in Symptoms. Intermittent Conditions