Subaru 2009 IMPREZA Service Manual page 1713

Diagnostic Trouble Code (DTC) Detecting Criteria
Leak Diagnosis
DTC
P0441 Evaporative emission system incorrect purge flow
P0442 Evaporative Emission Control System Leak Detected (Small Leak)
P0457 Evaporative Emission Control System Leak Detected (Fuel Cap Loose/Off)
• The diagnostic consists of creating a sealed vacuum in the fuel tank and then determining the presence of
leakage from the speed at which the tank internal pressure returns to barometric pressure.
• The diagnosis is divided into the following five phases.
Mode A: (Estimated evaporation gas amount)
Calculate the tank pressure change amount (P1) when using mode A. After calculating P1, switch to mode B.
Mode B: (Negative pressure sealed)
Introduce negative pressure in the intake manifold to the tank.
Approx. 0 –1.4 kPa (0
When the pressure above (desired negative pressure) is reached, enters Mode C.
In this case, if the tank pressure does not reach the target negative pressure, judge that there is a large leak-
age in the system and terminate the evaporative emission control system diagnosis.
Abnormality Judgement
Judge as NG (large leakage) when the following conditions are established.
Judgement Value
Malfunction Criteria
Time to reach target negative pressure
or
Mode B time
(Min. pressure value in tank when in
mode B) – (Tank pressure when mode B
started)
Time Needed for Diagnosis: 0 ms + 3000 ms + 10000 ms + 10000 ms + 25000 ms
Mode C: (Check pressure rise)
Stop the introduction of negative pressure. (Wait until the tank pressure returns to the start level of P2 cal-
culation.)
Change to Mode D when the tank pressure returns to the start level of P2 calculation.
Judge immediate OK and change to Mode E when it does not return in spite of spending the specified time.
Tank pressure when starting cal-
culation of P2
–1.4 kPa (–10.5 mmHg, –0.4 inHg) 18600 ms
Time Needed for Diagnosis: 0 ms + 3000 ms + 10000 ms + 10000 ms + 25000 ms + 18600 ms
–10.5 mmHg, 0 –0.4 inHg)
Threshold Value
10000 ms + 25000 ms P0457
10000 ms
> –0.3 kPa (–2.5 mmHg,
–0.1 inHg)
Time for advanced OK
judgement
GD(H4DOTC)-125
GENERAL DESCRIPTION
DTC