09-110-23

ATTENTION:
GENERAL MANAGER
q
PARTS MANAGER
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CLAIMS PERSONNEL
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IMPORTANT - All
Service Personnel
Should Read and
Initial in the boxes
provided, right.
SERVICE MANAGER
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© 2023 Subaru of America, Inc. All rights reserved.
SERVICE INFORMATION BULLETIN
APPLICABILITY:
		
		
		
		
		
		
2017-19MY Legacy & Outback 2.5L
2020-23MY Legacy & Outback
2017-23MY Impreza & Crosstrek
2017-18MY Forester 2.5L
2019-23MY Forester
2017-23MY WRX
2019-21MY Ascent
NUMBER: 09-110-23
DATE: 10/09/23
SUBJECT: DTC P0420 Diagnostic Procedure
INTRODUCTION:
This Service Information Bulletin announces diagnostic service procedures to be followed when
DTC P0420 (Catalyst System Efficiency Below Threshold Bank 1) is detected by the Engine Control
Module (ECM). If DTC P0420 is found to be stored in the ECM, follow the diagnostic procedures
outlined below.
SERVICE PROCEDURE / INFORMATION:
STEP 1: Perform a general inspection. Refer to STIS: DIAGNOSTICS > ENGINE
(DIAGNOSTICS) > General Description. Has the fault source been detected during the general
inspection?
YES – Repair the fault source according to the procedures outlined in the applicable Service 		
Manual.
NO – Proceed to the next Step.
STEP 2: Using SSM, perform a fault scan. Are any of the following DTCs found to be stored?
•
P0300-P0304
•
P219C-P219F
•
P0171, P0172
•
P0030-P0032
•
P0131, P0132, P0134
•
P0137, P0138, P0140
•
P0037, P0038
•
P0141
CAUTION: VEHICLE SERVICING PERFORMED BY UNTRAINED PERSONS COULD
RESULT IN SERIOUS INJURY TO THOSE PERSONS OR TO OTHERS.
Subaru Service Bulletins are intended for use by professional technicians ONLY. They
are written to inform those technicians of conditions that may occur in some vehicles,
or to provide information that could assist in the proper servicing of the vehicle. Properly
trained technicians have the equipment, tools, safety instructions, and know-how to
do the job correctly and safely. If a condition is described, DO NOT assume that this
Service Bulletin applies to your vehicle, or that your vehicle will have that condition.
Subaru of America, Inc. is
ISO 14001 Compliant
ISO 14001 is the international standard for
excellence in Environmental Management
Systems. Please recycle or dispose of
automotive products in a manner that is friendly
to our environment and in accordance with all
local, state and federal laws and regulations.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 1 of 11
YES – Perform diagnosis for the DTC(s) using the procedures outlined in the applicable Service
Manual. Once diagnosed and repaired, perform the road test outlined in Step 6 to confirm the
repair. If DTC P0420 continues to be detected after the road test, continue the diagnosis by
proceeding to the following steps. If the DTC is not detected, the diagnosis is complete.
NO – Proceed to the next Step.
STEP 3: Confirm the engine oil level is at the proper level. Add oil if needed. Start the engine and
pulse the throttle while monitoring the tail pipe. Is any white smoke observed to be emitting from the
tailpipe?
YES – Diagnose and repair the mechanical portion of the engine using the procedures outlined
in the applicable Service Manual. Once diagnosis and repair(s) are completed, Replace the Front
Exhaust Pipe and the Center Exhaust Pipe then proceed to Step 6.
NO – Proceed to the next Step.
STEP 4: Perform an inspection of the exhaust system. Check for air leaks, loose hardware, or
physical damage on the following components.
•
Cylinder Heads
•
Front Exhaust Pipe
•
Catalytic Converter
•
A/F Sensor
•
Oxygen Sensor
Has the fault source been determined by the inspection?
YES – Perform the necessary repair following the procedure outlined in the applicable 			
Service Manual. Proceed to Step 7 to confirm the repair.
NO – Proceed to the next Step.
STEP 5: Perform an active test of the injection quantity control. This Test is located in the “Active
Test” section of SSM. Confirm the A/F sensor values reach the targeted fuel injection setting. See the
example images below.
Normal A/F sensor
Abnormal A/F sensor
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 2 of 11
Do the A/F sensor values reach the targeted fuel injection setting?
YES - Replace the front exhaust pipe and the center exhaust pipe then proceed to the next 		
Step.
NO – Replace the A/F sensor assembly then proceed to Step 7.
STEP 6: Perform a road test as per the “INSPECTION MODE V” requirements outlined below.
This procedure information can also be found in the applicable Service Manual. Refer to STIS:
DIAGNOSTICS > ENGINE (DIAGNOSTICS) > PROCEDURE
CAUTION: When performing the “INSPECTION MODE V” road test on public roads, pay special
attention to the traffic conditions and maintain safe driving practices.
Confirm the prerequisites listed below are met:
•
The engine is at normal operating temperature.
•
The battery health status is sufficient. Detailed battery testing and charging information can
be found in TSB 07-178-21R.
•
The fuel level must be approximately half full.
•
Using SSM, clear the fault memory of the ECM.
6-A: Perform a road test following the drive pattern descriptions below.
(1) Vehicle Speed 0 mph (2) Vehicle Speed 37 mph
(A)
Start the engine.
(B)
Idle the engine
for at least five
minutes.
(C)
Accelerate the vehicle to 37 mph.
(D)
Using the Subaru Select Monitor,
check the [Catalyst Temperature
#11] value and drive at a constant
speed of 37 mph until 500°C (932°F)
is reached.
(G)
Accelerate the vehicle to 37 mph.
From the state where [Catalyst TemFrom the state where [Catalyst Temperature #11] value is 500°C (932°F)
perature #11] value is 500°C (932°F)
or more and the vehicle speed is 60
or more and the vehicle speed is 37
(E)
(H) km/h (37 MPH), change the accelmph, change the accelerator opening
erator opening angle to 0% to stop
angle to 0% to perform fuel cut for at
the vehicle with fuel cut for at least
least 5 seconds.
5 seconds.
Drive the vehicle with 10 to 20 % of
Idle the engine for 20 seconds or
(F) the accelerator opening angle for at (I)
more.
least 10 seconds.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 3 of 11
NOTES:
•
The condition of acceleration and/or constant driving can be changed according to the
surrounding traffic conditions.
•
If diagnostic values have not been inputted after driving, repeat the cycle from section (C)
without turning the engine off.
6-B: Once the road test is completed, read the OBD MODE test results using SSM.
Read the following data monitor value:
BDMID - $21 TID - $89 Scaling ID - $3B (Catalyst Deterioration Diagnosis Bank 1)
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 4 of 11
Is The value shown HIGHER than the applicable value listed in the table below?
Model
Engine Specification & Applicable MY
Road Test 1
2.5L 17MY-
0.45
2.5L 20MY-
0.4
2.4L DIT 20MY-
0.5
2.5L 17MY-
0.45
2.5L 19MY-
0.4
2.0L 17MY CROSSTREK
0.55
2.0L 2.5L 17MY- IMPREZA
2.0L 2.5L 18MY- CROSSTREK
0.4
Plug-in HYBRID 19MY-
0.4
19 - 21MY
0.5
2.5L Turbo 18-21MY
0.6
2.4L DIT 22MY-
0.7
2.4L 22MY-
0.35
LEGACY/OUTBACK
FORESTER
IMPREZA/CROSSTREK
ASCENT
WRX
BRZ/GR86
YES – The diagnosis is complete.
NO – Proceed to the Step 8.
STEP 7: Perform a road test as per the “INSPECTION MODE V” requirements outlined below.
This procedure information can also be found in the applicable Service Manual. Refer to STIS:
DIAGNOSTICS > ENGINE (DIAGNOSTICS) > PROCEDURE
CAUTION: When performing the “INSPECTION MODE V” road test on public roads, pay special
attention to the traffic conditions and maintain safe driving practices.
Confirm the prerequisites listed below are met:
•
The engine is at normal operating temperature.
•
The battery health status is sufficient. Detailed battery testing and charging information can be
found in TSB 07-178-21R.
•
The fuel level must be approximately half full.
•
Using SSM, clear the fault memory of the ECM.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 5 of 11
7-A: Perform a road test following the drive pattern descriptions below.
(2) Vehicle Speed 0 mph (2) Vehicle Speed 37 mph
(A)
Start the engine.
(B)
Idle the engine
for at least five
minutes.
(C)
Accelerate the vehicle to 37 mph.
(D)
Using the Subaru Select Monitor,
check the [Catalyst Temperature
#11] value and drive at a constant
speed of 37 mph until 500°C (932°F)
is reached.
(G)
Drive the vehicle with 10 to 20 % of
the accelerator opening angle for at
least 10 seconds.
(I)
Accelerate the vehicle to 37 mph.
From the state where [Catalyst TemFrom the state where [Catalyst Temperature #11] value is 500°C (932°F)
perature #11] value is 500°C (932°F)
or more and the vehicle speed is 60
or more and the vehicle speed is 37
(E)
(H) km/h (37 MPH), change the accelmph, change the accelerator opening
erator opening angle to 0% to stop
angle to 0% to perform fuel cut for at
the vehicle with fuel cut for at least
least 5 seconds.
5 seconds.
(F)
Idle the engine for 20 seconds or
more.
NOTES:
•
The condition of acceleration and/or constant driving can be changed according to the
surrounding traffic conditions.
•
If diagnostic values have not been input after driving, repeat the cycle from section(C)
without turning the engine off.
7-B: Once the road test is completed, read the OBD MODE test results using SSM.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 6 of 11
Read the following data monitor value:
BDMID - $21 TID - $89 Scaling ID - $3B (Catalyst Deterioration Diagnosis Bank 1)
Is The value shown HIGHER than the applicable value listed in the table below?
Model
Engine Specification & Applicable MY
Road Test 2
2.5L 17MY-
0.35
2.5L 20MY-
0.2
2.4LDIT 20MY-
0.3
2.5L 17MY-
0.35
2.5L 19MY-
0.2
LEGACY/OUTBACK
FORESTER
2.0L 17MY CROSSTREK
IMPREZA/CROSSTREK
0.35
2.0L 2.5L 17MY- IMPREZA
2.0L 2.5L 18MY- CROSSTREK
0.2
Plug-in HYBRID 19MY-
0.21
ASCENT
WRX
BRZ/GR86
19 - 21MY
0.25
2.5L Turbo 18-21MY
0.3
2.4L DIT 22MY -
0.15 (CVT)
0.25 (MT)
2.4L 22MY-
0.15
YES – The diagnosis is complete.
NO – Replace the front exhaust pipe and the center exhaust pipe. Proceed to Step 6.
STEP 8: Perform an inspection of the Exhaust Gas Recirculation system. Check for gas leaks and/or
vacuum leaks along the piping of the following sections:
NOTE: Contamination and carbon deposits can be an indication of leakage and/or vacuum leaks.
•
Fitting/Connection of flanges
•
Electronic Throttle
•
Manifold Pressure and Intake Air Temperature Sensor.
•
EGR Control Valve
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 7 of 11
Has any leakage and/or vacuum leaks been detected?
YES – Repair the necessary component and then proceed to Step 10.
NO – Proceed to Step 9.
STEP 9: Start the engine and allow it to reach normal operating temperature. Using SSM, read
the data monitor value of the rear oxygen sensor. Move the oxygen sensor harness by hand while
monitoring the waveform.
Has an abnormal operation been displayed while moving the rear oxygen sensor harness by hand?
YES – Replace or repair the affected electrical connection and then proceed to Step 10.
NO – Restart the procedures from Step 1. Confirm the previous testing was not impaired by any
temporary/momentary conditions. NOTE: there is no need to replace the exhaust components
that have been previously replaced using the procedures outlined in this bulletin.
STEP 10: Perform a road test as per the “INSPECTION MODE V” requirements outlined below.
This procedure information can also be found in the applicable Service Manual. Refer to STIS:
DIAGNOSTICS > ENGINE (DIAGNOSTICS) > PROCEDURE
CAUTION: When performing the “INSPECTION MODE V” road test on public roads, pay special
attention to the traffic conditions and maintain safe driving practices.
Confirm the prerequisites listed below are met:
•
The engine is at normal operating temperature.
•
The battery health status is sufficient. Detailed battery testing and charging information can be
found in TSB 07-178-21R.
•
The fuel level must be approximately half full.
•
Using SSM, clear the fault memory of the ECM.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 8 of 11
10-A: Perform a road test following the drive pattern descriptions below.
(3) Vehicle Speed 0 mph (2) Vehicle Speed 37 mph
(A)
Start the engine.
(B)
Idle the engine
for at least five
minutes.
(C)
Accelerate the vehicle to 37 mph.
(D)
Using the Subaru Select Monitor,
check the [Catalyst Temperature
#11] value and drive at a constant
speed of 37 mph until 500°C (932°F)
is reached.
(G)
Accelerate the vehicle to 37 mph.
From the state where [Catalyst TemFrom the state where [Catalyst Temperature #11] value is 500°C (932°F)
perature #11] value is 500°C (932°F)
or more and the vehicle speed is 60
or more and the vehicle speed is 37
(E)
(H) km/h (37 MPH), change the accelmph, change the accelerator opening
erator opening angle to 0% to stop
angle to 0% to perform fuel cut for at
the vehicle with fuel cut for at least
least 5 seconds.
5 seconds.
Drive the vehicle with 10 to 20 % of
Idle the engine for 20 seconds or
(F) the accelerator opening angle for at (I)
more.
least 10 seconds.
NOTES:
•
The condition of acceleration and/or constant driving can be changed according to the
surrounding traffic conditions.
•
If diagnostic values have not been input after driving, repeat the cycle from section(C) without
turning the engine off.
10-B: Once the road test is completed, read the OBD MODE test results using SSM.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 9 of 11
Read the following data monitor value:
BDMID - $21 TID - $89 Scaling ID - $3B (Catalyst Deterioration Diagnosis Bank 1)
Is The value shown HIGHER than the applicable value listed in the table below?
Model
Engine Specification & Applicable MY
Final Road Test
2.5L 17MY-
0.45
2.5L 20MY-
0.4
2.4LDIT 20MY-
0.5
2.5L 17MY-
0.45
2.5L 19MY-
0.4
2.0L 17MY CROSSTREK
0.55
2.0L 2.5L 17MY- IMPREZA
2.0L 2.5L 18MY- CROSSTREK
0.4
Plug-in HYBRID 19MY-
0.4
19-21MY
0.5
2.5L TC 18-21MY
0.6
2.4L DIT 22MY-
0.7
2.4L 22MY-
0.35
LEGACY/OUTBACK
FORESTER
IMPREZA/CROSSTREK
ASCENT
WRX
BRZ/GR86
YES - The diagnosis is complete.
NO - Perform the basic diagnosis procedure as per the applicable Service Manual. Refer to STIS:
DIAGNOSTICS > ENGINE (DIAGNOSTICS) > Basic Diagnostic Procedure.
NOTE: there is no need to replace the exhaust components that have been previously replaced
using the procedures outlined in this bulletin.
Continued...
Bulletin Number: 09-110-23; Date: 10/09/23
Page 10 of 11
WARRANTY / CLAIM INFORMATION:
No changes have been made to the current Warranty Labor Time Guide for this procedure. Below
are Failure Code examples to assist with searching, please refer to the Labor Time Guide for the
respective operation/ labor time and Warranty Coverage.
Labor Description
Fail Code
Oxygen Sensor/Air Fuel Ratio Sensor
UFP
OBDII Rear Oxygen Sensor
UEF
EGR Valve Gasket
HAD
Front Catalytic Converter
HCR
O Ring/Gasket, Throttle Body
DDL
IMPORTANT REMINDERS:
•
SOA strongly discourages the printing and/or local storage of service information as previously
released information and electronic publications may be updated at any time.
•
Always check for any open recalls or campaigns anytime a vehicle is in for servicing.
•
Always refer to STIS for the latest service information before performing any repairs.
Bulletin Number: 09-110-23; Date: 10/09/23
Page 11 of 11