Subaru LEGACY 2006 Manual page 568

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Diagnostic Trouble Code (DTC) Detecting Criteria
Diagnostic method
• The diagnostic method 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 atmospheric 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.
Approximately 0 → –1.4 kPa (0 → –10.5 mmHg, 0 → –0.41 inHg)
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 (10 seconds or 25 seconds) in the system and terminate the evaporative emission control system diag-
nosis.
Abnormality Judgment
Judge as NG (large leak) when the criteria below are met.
Judgment 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)
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
–1.3 kPa (–9.75 mmHg, –0.38
inHg)
Mode D: (Measure amount of negative pressure change)
Monitor the tank pressure change amount when using mode D. In this case, the tank pressure increases,
(nears atmospheric pressure) because evaporation occurs. However, if any leakage exists, the pressure in-
creases additionally in proportion to this leakage. The pressure variation of this tank is P2.
After calculating P2, perform a small leak diagnosis according to the items below.
When Mode D is ended
Assign tank variations measured in Mode A and Mode D; P1 and P2, to the formula below, judge small leaks
in the system. If the measured judgment value exceeds the threshold value, it is judged to be a malfunction.
Abnormality Judgment
Judge as NG when the criteria below are met and judge as OK when not met, and clear NG.
Judgment Value
Malfunction Criteria
P2 – 1.5 × P1
P2: Tank pressure that changes every 10
seconds in mode D
P1: Tank pressure that changes every 10
seconds in mode A
* 1.5: Evaporation amount compensation value when below negative pressure (Amount of evaporation occurrence increases as
a vacuum condition increases.)
Threshold Value
≥ 25 sec.
≥ 10 sec.
< –0.33 kPa
(–2.5 mmHg, –0.097
inHg)
Time for advanced OK
judgment
15 seconds
Threshold Value
> Value from Map 7
* Threshold value:
Map (Remaining Fuel
vs Tank temperature)
GD(H4SO)-131
GENERAL DESCRIPTION
DTC
P0457
DTC
P0442