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Home >> Subaru >> 2006 >> Legacy GT spec.B >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 15 (Diagnostic Trouble Code (DTC) Detecting Criteria (H4SO)) >> Diagnostic Trouble Code (DTC) Detecting Criteria >> DTC P0442 Evaporative Emission Control System Leak Detected (Small Leak) >> Outline Of Diagnosis

Outline Of Diagnosis

WARNING: This page is about a different variant/trim than selected.

Check if there is a leakage in fuel system or not, and perform the function diagnosis of valve.

Fig 1: Evaporative Emission Control System Diagram
G05017676

In this system diagnosis, check for leakage and valve function is conducted by changing the fuel tank pressure and monitoring the pressure change using the fuel tank pressure sensor. When in 0.04 inch diagnosis, perform in the order of mode Z → mode A → mode B → mode C and mode D; When in 0.02 inch diagnosis, perform in the order of mode A → mode B → mode C → mode D and mode E.

0.04-inch Diagnosis 

Fig 2: 0.04-Inch Diagnosis Mode Description Chart
G04998198
MODE DESCRIPTION CHART

Mode Mode Description Diagnosis Period
Mode Z (Purge control solenoid valve opening failure diagnosis) Perform purge control solenoid valve opening failure diagnosis from the size of tank pressure variation from diagnosis start. 3 - 16 seconds
Mode A (Estimated evaporation amount) Calculate the tank pressure change amount (P1). 10 seconds
Mode B (Sealed negative pressure, large leakage judgment) Decrease the pressure in the tank to the target value by introducing the intake manifold pressure to the fuel tank. If the tank pressure cannot be reduced, it is diagnosed as large leak. 5 - 25 seconds
Mode C (Pressure increase check, advanced OK judgment) Wait until the tank pressure returns to the target (start level of P2 calculation). If the tank pressure does not become the value, make advanced OK judgment. 1 - 15 seconds
Mode D (Negative pressure variation measurement, evaporation leakage diagnosis) Calculate the tank pressure variation (P2), and obtain the diagnostic value using P1 found in Mode A. Perform the evaporation diagnosis using the diagnostic value. 10 seconds

Mode Table for Evaporative Emission Control System Diagnosis 

MODE DESCRIPTION CHART

Mode Behavior of tank internal pressure under normal conditions Diagnostic item DTC
Mode Z Roughly the same as atmospheric pressure (Same as 0 kPa (0 mmHg, 0 inHg)) Purge control solenoid valve is judged to be open. P0457
Mode A Pressure is in proportion to amount of evaporative emission.    
Mode B Negative pressure is formed due to intake manifold negative pressure Large leak P0457
Mode C Reaches target pressure   None
Mode D Pressure change is small. EVAP system large leak determination. [1.0 mm (0.04 in)] P0442

0.02-inch Diagnosis 

Fig 3: 0.02-Inch Diagnosis Mode Description Chart
G04998199
MODE DESCRIPTION CHART

Mode Mode Description Diagnosis Period
Mode A (0 point compensation) When the pressure in the tank is high, wait until it returns to 0 point (Near 0 mmHg,). 0 - 12 seconds
Mode B (Negative pressure introduced) Decrease the pressure in the tank to the target value by introducing the intake manifold pressure to the fuel tank. 0 - 27 seconds
Mode C (Negative pressure maintained) Wait until the tank pressure returns to the target (start level of P2 calculation). 0 - 20 seconds
Mode D (Negative pressure change calculated) Calculate the time it takes for the tank pressure to return to the P2 calculation complete pressure. If the tank pressure does not return to the P2 calculation complete pressure, make advanced OK judgment. 0 - 200 seconds
Mode E (Evaporation generated amount calculation) Calculate the amount of evaporation (P1). 0 - 280 seconds