LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Subaru >> 2021 >> WRX STI >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (Diagnostics) (2.5L) (2 Of 4) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0455: EVAP System (CPC) Leak Detected (Large Leak) >> Diagnostic Method
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Method

G12456829Courtesy of SUBARU OF AMERICA, INC.
Mode Explanation of Mode Diagnosis Period
A Vacuum pump operation confirmation and characteristics stability 7 s
B Measurement of reference pressure for setting the target negative pressure 350 s
C Switching valve operation confirmation 12 s
D Pipe clogging diagnosis and leak pressure measurement 900 s
D2 Pipe clogging diagnosis of high-pressure line 60 s
E Reference pressure measurement for judgment 50 s
G10291032Courtesy of SUBARU OF AMERICA, INC.

Mode A (Vacuum pump operation confirmation and characteristics stability) 

Purpose: Detect the vacuum pump operation trouble.

Judge as NG when the following conditions are established.

Judge as OK if the following conditions are not established, and warm up for five minutes to stabilize the vacuum pump characteristics.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value DTC
Pressure sensor output value > -224Pa (-1.68 mmHg, -0.1 inHg) P2404

Mode B (Measurement of reference pressure for setting the target negative pressure) 

Judgment 1

Purpose: Judge the reference pressure stability.

Judgment 2

Purpose: Judge whether the reference pressure is within the normal range, and detect the vacuum pump and orifice malfunctions.

Judge as NG when the following conditions are established.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value DTC
Judgment 1   P2404
|Pressure sensor maximum output value - Pressure sensor minimum output value| > 314Pa (2.355 mmHg, 0.1 inHg)  
or    
Judgment 2    
Reference pressure for setting the target negative pressure < Value of Map 2  
or    
Judgment 3    
Reference pressure for judgment > Value of Map 3  
MAP 2 SPECIFICATION

Barometric pressure (kPa (mmHg, inHg)) 70 (525, 20.7) 80 (600, 23.6) 90 (675, 26.6) 100 (750, 29.5)
Reference pressure for setting the target negative pressure (kPa (mmHg, inHg)) -4 (-29.79, -1.2) -4.1 (-30.593, -1.2) -4.2 (-31.395, -1.2) -4.3 (-32.19, -1.3)
MAP 3 SPECIFICATION

Barometric pressure (kPa (mmHg, inHg)) 70 (525, 20.7) 80 (600, 23.6) 90 (675, 26.6) 100 (750, 29.5)
Reference pressure for setting the target negative pressure (kPa (mmHg, inHg)) -0.9 (-7.065, -0.3) -1 (-7.86, -0.3) -1.2 (-8.663, -0.3) -1.3 (-9.465, -0.4)

Mode C (Switching valve operation confirmation) 

Purpose: Measure the pressure increase when switching valve is changed from open to close, and detect the stuck to open/close malfunctions of the switching valve.

Judge as NG when the following conditions are established.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value DTC
Pressure sensor output value - Reference pressure for setting the target negative pressure < 224Pa (1.68 mmHg, 0.1 inHg) P2404

Mode D (Clogging of pipe diagnosis and leak pressure measurement) 

  1. Clogging of pipe 

    Purpose: Measure the time required for the evaporative emission system to reach the target negative pressure by the vacuum pump, and detect the clogging of pipe trouble.

    Judge as clogging of pipe malfunction if the evaporative emission system reaches to the target negative pressure within the specified time.

  2. Leak pressure measurement 

Purpose: Measure the pressure (leak pressure) when the evaporative emission system becomes the negative pressure by the vacuum pump.

Store the pressure as a leak pressure while the following conditions are met.

Phase D

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value DTC
Phase D    
Time for reaching the target ≤27000 ms P1451
Phase D2    
Reference pressure for setting the target negative pressure < -0.7 kPa
(-5 mmHg, -0.2 inHg)
P04AF
<Large leak (0.04 inch)>   P0455
Leak pressure ≥ Value of Map 6
<Very small leak (0.02 inch)>   P0456
Leak pressure > Reference pressure of 0.018 inch (Pa)
and
< Value of Map 6
 
MAP 6 SPECIFICATION

Reference pressure (Pa) -4856 -4000 -2750 -1500 -824
Threshold Value (Pa) -1785 -1463 -991 -520 -265

Formula for threshold value = Reference pressure x0.377-0.341 mmHg

Time needed for diagnosis:  24 min

Mode E (Measurement of reference pressure for judgment) 

Judgment 1

Purpose: Judge the reference pressure stability.

Judge as NG when the following conditions are established.

Judgment 2

Purpose: Judge whether the reference pressure is within the normal range, and detect the vacuum pump and orifice malfunctions.

Judge the vacuum pump performance stability.

Judge as NG when the following conditions are established.

Judgment 3

Purpose: Judge the presence of evaporative emission system leak.

Judge as NG when the following conditions are established.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value DTC
Judgment 1
|Pressure sensor maximum output value - Pressure sensor minimum output value|
> 314Pa (2.355 mmHg, 0.1 inHg) P2404
or    
Judgment 2
Reference pressure for judgment
< Value of Map 4
or
> Value of Map 5
P2404
or    
Judgment 3
|Reference pressure for setting the target negative pressure - Reference pressure for judgment|
> 941Pa (7.058 mmHg, 0.3 inHg) P2404
MAP 4 SPECIFICATION

Barometric pressure (kPa (mmHg, inHg) 70 (525, 20.7) 80 (600, 23.6) 90 (675, 26.6) 100 (750, 29.5)
Reference pressure for judgment (kPa (mmHg, inHg)) -4.5 (-34.02, -1.3) -4.6 (-34.815, -1.4) -4.7 (-35.618, -1.4) -4.9 (-36.42, -1.4)
MAP 5 SPECIFICATION

Barometric pressure (kPa (mmHg, inHg)) 70 (525, 20.7) 80 (600, 23.6) 90 (675, 26.6) 100 (750, 29.5)
Reference pressure for judgment (kPa (mmHg, inHg)) -0.8 (-6.18, -0.2) -0.9 (-6.983, -0.3) -1 (-7.785, -0.3) -1.1 (-8.58, -0.3)

Time needed for diagnosis:  Approx. 24 min

Malfunction will be confirmed at next engine start.

Malfunction indicator light illumination:  Illuminates when malfunction occurs in 2 continuous driving cycles.