ATTENTION:
GENERAL MANAGER

q

PARTS MANAGER

q

CLAIMS PERSONNEL

q

IMPORTANT - All
Service Personnel
Should Read and
Initial in the boxes
provided, right.

SERVICE MANAGER

q

© 2024 Subaru of America, Inc. All rights reserved.

SERVICE BULLETIN
APPLICABILITY:

2020-24MY Legacy and Outback 2.5L NA
and 2.4L DIT
2018-24MY Crosstrek
2017-24MY Impreza
2019-24MY Forester 2.5 NA
2014-18MY Forester 2.0L DIT
2015-24MY WRX 2.0 DIT
2019-24MY Ascent

NUMBER: 02-193-24R

SUBJECT:

Walnut Blast Cleaning Procedure for Carbon
Deposit Removal to Address Engine Misfire DTCs,
Black Smoke from the Exhaust, Lack of Power,
Knocking (Ping) and / or Rough Idle Concerns

DATE: 02/16/25
REVISED: 02/17/25

INTRODUCTION:
This bulletin provides updated parts information and a service procedure to follow for removing
accumulated carbon deposits from fuel injectors and internal engine components (e.g. intake valves
and / or manifold, and combustion chambers). Fuel quality and how the vehicle is operated are both
major contributing factors which will have a direct effect on carbon deposit accumulation. This
cleaning procedure for carbon deposit removal is recommended to address engine misfire DTCs,
black smoke from the exhaust, lack of power, knocking (ping) and / or rough idle concerns. The
procedure outlines the use of an Autool HTS558 Walnut Blasting Machine that has been approved by
Subaru of America.
IMPORTANT: This procedure was developed as a suitable alternative to the procedures outlined in
09-74-21R due to available retailer equipment. ONLY one procedure can be reimbursed by Warranty.
REQUIRED TOOLS:

WALNUT BLASTING MACHINE
AUTOOL HTS558

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: 02-193-24R; Revised: 02/17/25

Page 1 of 11

WALNUT SHELL MEDIA
Grit Size: #24orSAE 18/40
Amount: Approximately 1-2lbs

SHOP TOWELS
Size: 14in x 12in
Quantity: As Needed

MOVING BLANKET
Size: 40in x 72in
Quantity: 2

MASKING TAPE
Recommended Size：1.88in(48mm)

SEAL PICK TOOLS
Tip shape: 90°, 45°
Length: Approx 6.3in(160mm) or more

CAP
SOA Part Number: 16519AA100
NOTE: Can be ordered through Subaru Parts
Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 2 of 11

SUBARU THROTTLE PLATE CLEANER
SOA Part Number: SOA868V9170
NOTE: Can be ordered through Subaru Parts

P.E.A. (POLYETHERAMINE) CARBON CLEANER
SOA Part Number SOA868V9166
NOTE: Fuel tank additive

SERVICE PROCEDURE / INFORMATION:
STEP 1: Refer to the applicable Service Manual and review: General Description > Repair Contents
> Action required before & after Battery Disconnect. Additionally, record any stored seat position(s)
before proceeding. Relearn any seat position memory after work is complete. If the power rear gate
(PRG) height has been customized, that position must also be noted and relearned.
STEP 2: Remove the battery as per the applicable Service Manual: Engine > STARTING/
CHARGING SYSTEMS > Battery > Removal
STEP 3: Remove the intake manifold as per the applicable Service Manual: Engine > FUEL
INJECTION (FUEL SYSTEMS) > Intake Manifold Assembly > Removal
IMPORTANT CAUTIONS:
•

The Service Manual uses a black star (★) in the component breakdown illustrations to
indicate one-time use parts.

•

It is vital to confirm no foreign matter enters any fuel lines, intake ducts, and any other
peripheral parts.

•

2.0L & 2.5L DINA equipped models DO NOT require fuel delivery tube disconnection

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 3 of 11

STEP 4: Cover/seal the required areas indicated in the model specific images below. Proceed to Step
5 for 2.0L & 2.5L DINA equipped models.
2.0L DIT & 2.4L DIT: Cover the turbo charger duct opening with making tape.

2.4L DIT: Install the cap (p.n. 16519AA100) on to the high pressure fuel pump connection.

STEP 5: Rotate the crank pully clockwise until the timing mark matches the position indicated
below.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 4 of 11

STEP 6: Visually inspect the intake valves of cylinders #1 and #3. Confirm the valves are in the
closed position.

NOTE: If the valves are open, rotate the crank pully 360 degrees in the clockwise direction and
monitor the valve position. DO NOT continue until the valves are confirmed to be closed.

STEP 7: Seal the intake ports of cylinders #2 and
#4 with masking tape. This will prevent any foreign
material from entering.

CAUTION: Contamination or adhesion of foreign
material such as walnut shell media
inside the engine may cause starting failure
and/or engine stalling.

STEP 8: Cover the area around the intake port with two moving blankets. This will help prevent any
walnut shell material from contamination.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 5 of 11

CAUTION: Confirm harness connections, fuels lines, and ALL other components are covered prior
to cleaning.

STEP 9: Prepare the walnut blasting machine (AUTOOL HTS558) with the necessary air supply.
Always use NEW abrasive material when performing cleaning.

STEP 10: Prepare the angled suction hose by inserting the square yellow adapter onto the end of the
hose. Allow approximately 10mm of the hose to protrude from the adapter. This will provide added
stability when cleaning.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 6 of 11

STEP 11: Set the hose into the cylinder #1 intake port. Cover any gaps with a shop towel.

STEP 12: Clean the intake valve and intake port of cylinders #1.
A. Confirm the walnut blaster is turned on.
B. Insert the nozzle of the walnut blaster into the suction hose.
C. Pull the trigger and allow the abrasive material to pass through the nozzle.
D. Aim the nozzle in the direction of Valve A.
E. Aim the nozzle in the direction of Valve B.
F. Move the nozzle up, down, left, and right to ensure the entire area is cleaned.

CAUTION: DO NOT remove the nozzle from suction hose while blasting the abrasive material.
This can cause contamination to the surrounding area.

TIP: A seal pick can be used for the removal of
some of the more difficult to remove carbon deposits.
Be careful not to scratch the valves or cylinder head.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 7 of 11

STEP 13: Repeat the cleaning process outlined in Step 12 for cylinder #3.
STEP 14: After cleaning is completed, remove any remaining abrasive material using the suction
hose. Using a flashlight, inspect the ports and confirm there is no remaining material.

STEP 15: Remove the moving blankets and masking tape covering the intake ports on cylinders #2
and #4.
CAUTION: Be mindful not to spread any of the abrasive material collected by the blankets into the
engine area.
STEP 16: Rotate the crank pully clockwise 360 degrees until the timing mark matches the position
indicated below.

STEP 17: Visually inspect the intake valves of cylinders #2 and #4. Confirm the valves are in the
closed position.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 8 of 11

STEP 18: Seal the intake ports of cylinders #1 and #3 with
masking tape. This will prevent any foreign material from
entering.
CAUTION: Contamination or adhesion of foreign material
such as walnut shell media inside the engine may cause
starting failure and/or engine stalling.

STEP 19: Cover the area around the intake port with two moving blankets. This will help prevent any
walnut shell material from contamination.

CAUTION: Confirm harness connections, fuels lines, and ALL other components are covered prior
to cleaning.

STEP 20: Repeat the procedures outlined in Steps 9 through 15 on cylinders #2 and #4.

Continued...
Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 9 of 11

STEP 21: Clean the plate and stick portions of all the cylinder head plates using throttle plate cleaner.
Dry the cylinder head plates with a clean shop towel. Confirm there is no cleaner remaining on the
plates.

STEP 22: Clean the throttle body.
A. Remove the throttle body from the intake manifold.
B. Soak a shop towel in throttle plate cleaner.
C. Wipe the throttle valve and bore inner surfaces from both the intake manifold and intake
duct sides.
D. Wipe the cleaned areas with a clean shop towel and confirm no throttle plate cleaner remains.

CAUTION: DO NOT open and close the throttle valve manually during cleaning. DO NOT deform
or scratch the throttle valve/bore.
STEP 23: Reinstall all parts in the reverse order of disassembly.
STEP 24: Fill the fuel tank fuel. Add one bottle of P.E.A. carbon cleaner (SOA868V9166) the fuel
tank.
NOTES:
•

The Service Manual uses a black star (★) in the component breakdown illustrations to
indicate one-time use parts.

•

Whenever reconnecting the ground cable terminal to the battery sensor, torque to 7.5Nm
(5.5ft.-lbs. or 66inch-lbs.) while supporting the sensor with the other hand as outlined in the
applicable Service Manual under: STARTING/CHARGING SYSTSEMS > Battery Sensor.
Continued...
Continued...

Bulletin Number: 02-193-24R; Revised: 02/17/25

Page 10 of 11

WARRANTY / CLAIM INFORMATION:
For vehicles within the Powertrain Limited Warranty period, this repair may be submitted using the
following claim information:
NOTE: This procedure was developed as a suitable alternative to the procedures outlined in 09-7421R due to available retailer equipment. ONLY one procedure can be reimbursed by Warranty.
Labor Description

Labor Operation #

Repair Code

ROUGHNESS DIAGNOSIS & MEDIA
CLEANING INTAKE PORTS

A449-286

BON-22

Labor Time / Aspiration
3.0h NA
3.6h Turbo

The claimable Warranty Part Number for 1 (one) bottle of the P.E.A. cleaner is SOA635328.
Add: Up to $2.00 can be claimed as Sublet for this repair for Walnut Shell Media

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: 02-193-24R; Revised: 02/17/25

Page 11 of 11