NHTSA ID Number: 11028515
Manufacturer Communication Number: A26-001
TSB/Document Date: 2026-02-06
Summary
Service Bulletin - The piston ring function deteriorates due to ring low wear toughness and sticking from sludge. Oil adheres to the spark plug leading to carbon fouling and misfire. This can set DTCs P0301 No. 1 cylinder misfire detected, P0302 No. 2 cylinder misfire detected, P0303 No. 3 cylinder misfire detected, P0304 No. 4 cylinder misfire detected, and cause the MIL to come on.
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TSB/Document ID: A26-001
Replacement Service Bulletin Number:
MFR Communication Date: 2026-02-01
MFR Internal Campaign ID/Software Version:
Communication Type: Service Bulletin/Repair Instructions
NHTSA Components: ENGINE
MFR Component System:
MFR Component Subsystem:
Previous TSB | Next TSB |
Gasket Remover/Pan Separator
Piston Ring Expander
Piston Ring Compressor
NOTE: Each dealer has been sent one cylinder wall inspection tool.
Repair Procedure B
Tool Name
Part Number
Quantity
KLS6227500
1
Engine hoist
NRI78106A or equivalent
1
Load leveler
NRI78115H
1
07AAJ-R70A301
1
Lift table
Cylinder Wall Inspection Tool
NOTE: Each dealer has been sent one cylinder wall inspection tool.
Page 8 of 65
INSPECTION PROCEDURE
1. Connect the HDS and do an ALL DTC check for the following DTCs:
NOTE: Print the results of the ALL DTC check; this will be needed for the warranty claim submission.
•
•
•
•
P0301 No. 1 Cylinder Misfire Detected
P0302 No. 2 Cylinder Misfire Detected
P0303 No. 3 Cylinder Misfire Detected
P0304 No. 4 Cylinder Misfire Detected
Are any of these DTCs stored?
YES – Go to step 2.
NO – Stop. This bulletin does not apply. Continue with normal troubleshooting.
2. Relieve the fuel pressure. (Click Here)
3. Remove the engine cover, then remove the appropriate ignition coils, and spark plugs based on the DTCs stored.
Example: If P0301 is stored, remove the ignition coil on cylinder No. 1.
Page 9 of 65
4. Remove and check the spark plug(s) of the affected cylinder(s).
Example: If P0301 is stored, check the spark plug on cylinder No. 1.
DTCs Stored
P0301
P0302
P0303
P0304
P0305
P0306
Diagnostic
Remove the #1 cylinder spark plug
and inspect for fouling.
Remove the #2 cylinder spark plug
and inspect for fouling.
Remove the #3 cylinder spark plug
and inspect for fouling.
Remove the #4 cylinder spark plug
and inspect for fouling.
Spark Plug
Condition?
Repair Process
Not fouled
This bulletin does not apply. Continue with
normal troubleshooting.
Fouled
Proceed to step 5.
Not fouled
This bulletin does not apply. Continue with
normal troubleshooting.
Fouled
Proceed to step 5.
Not fouled
This bulletin does not apply. Continue with
normal troubleshooting.
Fouled
Proceed to step 5.
Not fouled
This bulletin does not apply. Continue with
normal troubleshooting.
Fouled
Proceed to step 5.
This bulletin does not apply. Continue with
normal troubleshooting.
Page 10 of 65
5. Remove the affected cylinder head(s) to inspect the cylinder bores.
DTCs Stored with
fouled spark plug(s)
P0301, P0302, or P0303
P0304
Diagnostic
Remove the rear cylinder head and inspect cylinder bores 1-3 for scratching or
scoring using the cylinder wall inspection tool.
Remove the front and rear cylinder heads and inspect cylinder bores 1-4 for
scratching or scoring using the cylinder wall inspection tool.
NOTICE
•
•
•
Use fender covers to avoid damaging painted surfaces.
To avoid damaging any wires and terminals, unplug the circuit connectors carefully while holding the
connector portion.
Mark all the circuits and hoses to avoid misconnection. Make sure they do not contact other circuit wiring, hoses,
or interfere with other parts.
1. Remove both front wheels so you can fully lower the vehicle.
2. Disconnect and remove the 12-volt battery. (Click Here)
3. Disconnect the fuel feed hose line at the bulkhead.
6. Remove the radiator cap.
7. Raise the vehicle.
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8. Remove the front splash shield.
9. Drain the engine oil.
10. Loosen the drain plug on the radiator and drain the coolant.
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11. Drain the remaining coolant from the engine by installing a 5/16in. inner diameter rubber hose (commercially available)
onto the block drain bolt located at the rear of the engine block, then loosen the drain bolt. Then disconnect the oil
pressure switch connector.
12. Remove exhaust pipe A, with under-floor TWC still attached. (Click Here)
13. Depending on the diagnosis, remove the appropriate WU-TWC support bracket bolts. (Click Here)
14. Remove the EGR lower pipe nuts (A).
15. Remove the right fender liner.
16. Lower the vehicle.
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17. Disconnect the MAP sensor connector and the breather pipe, then remove the intake air duct.
18. Disconnect the PCV hose (A), the brake booster vacuum hose (B), and the IMT actuator connector (C).
19. Disconnect the EVAP canister hose (A), the EVAP canister purge valve connector (B), the throttle actuator connector
(C), and the MAP sensor connector (D). Disconnect and plug the water bypass hoses (E).
20. Lift the power steering reservoir out of the bracket and remove the drive belt. (Click Here)
21. Remove the alternator. (Click Here)
Page 14 of 65
22. Remove the following. Do steps 6 and 7. (Click Here):
•
•
Engine intake upper cover and PCV hose
Remove the intake manifold bolts and nuts in three steps, then remove the intake manifold.
FOR INSTALLATION:
Install the intake manifold with a new intake manifold gasket. Tighten the bolts and nuts to 22 N·m (16 lb-ft) in three
steps in the sequence shown.
FOR INSTALLATION:
Install the upper cover (A) with a new gasket. Tighten the bolts and nuts to 12 N·m (8.9 lb-ft) in three steps in the
sequence shown below.
Page 15 of 65
23. Remove the power steering pump bolts, the power steering hose bracket then secure the power steering pump out of
the way.
NOTE: DO NOT remove any of the power steering hoses.
24. Remove the drive belt auto-tensioner. (Click Here)
25. Set the number 1 cylinder to TDC.
26. Remove the crankshaft pulley. Do steps 5 and 6. (Click Here)
Page 16 of 65
27. Remove the PCM cover.
28. Remove the harness clamps (A), then disconnect the PCM connectors (B), and the engine wire harness connector (C),
then remove the PCM with the bracket.
Page 17 of 65
29. Remove the ground cable bracket (A), then remove the upper side engine mount bracket (B).
30. Remove the front upper timing cover (A) and the rear upper timing cover (B).
31. Raise the vehicle.
32. Remove the lower timing cover.
33. Lower the vehicle.
Page 18 of 65
34. Remove the lower half of the side engine mount bracket.
35. Remove the timing belt auto-tensioner.
NOTE: See the service information procedure to compress the tensioner for installation.
36. Remove the timing belt. (Click Here)
37. Depending on the diagnosis, remove some or all of the following parts that are necessary:
•
•
•
•
•
•
•
•
•
•
•
•
ECT sensor 1 connector
Front rocker arm oil pressure switch connector
Rear rocker arm oil pressure switch connector
CMP sensor connector
Front A/F sensor 1 connector
Rear A/F sensor 1 connector
Front secondary HO2S connector
Rear secondary HO2S connector
Rocker arm oil control solenoid A connector (bank one)
Rocker arm oil control solenoid A connector (bank two)
Rocker arm oil control solenoid B connector (bank one)
Knock sensor connector
Page 19 of 65
38. Remove the quick-connect fitting cover, then disconnect the fuel feed hose.
39. Remove the EVAP canister purge joint with the bracket.
40. Remove the fuel rail connecting joint hose.
Page 20 of 65
41. Remove the upper EGR pipe mounting bolts, then remove the EGR pipe.
42. Remove upper and lower radiator coolant hoses.
Page 21 of 65
43. Separate the water passage from the cylinder heads, then remove the water passage assembly.
44. Remove the starter by removing the harness clamp (A), then disconnect the positive starter cable (B) and the S
terminal connector (C) from the starter. Remove the lower radiator hose bracket (D) and the dipstick (E), then remove
the starter assembly (F).
NOTE: Install with a new gasket (G).
Page 22 of 65
45. Remove the appropriate WU-TWC depending on diagnosis and set the WU-TWC aside.
NOTE: The WU-TWC can be set aside. Cover the opening with a shop towel to prevent coolant from entering.
46. Remove the appropriate head with the injector base attached.
NOTE:
• Depending on the diagnosis, you will remove the rear bank cylinder head or both cylinder heads.
• To prevent warpage, loosen the bolts in sequence, 1/3 turn at a time, repeat until all the bolts are loosened.
47. Measure the head bolts to determine if they need replacement. If either diameter is less than 11.3 mm (0.445 in.),
replace the cylinder head bolts before reassembly.
Page 23 of 65
48. Use the cylinder wall inspection tool to inspect the cylinder walls for vertical scratching.
NOTE:
• For information on using the cylinder wall inspection tool, refer to the Job Aid “Cylinder Wall Inspection Tool”
and/or Tech2Tech “Check out the Cylinder Wall Inspection Tool”.
• Do not use a fingernail or pencil lead to determine if an engine block is usable. Light to moderate scratches that
are detected with your fingernail will pass the inspection when using the cylinder wall inspection tool.
Check Out the Cylinder Wall Inspection Tool
Special tool (07AAJ-R70A301)
Determine the repair direction based on the cylinder inspection:
DTCs Stored
Cylinder Bore
Condition?
Repair Direction
Do Repair Procedure A:
No scratching detected
P0301, P0302,
or P0303
•
•
•
•
Clean pistons 1-3
Replace piston rings 1-3
Replace spark plugs 1-4
Update PCM software
Do Repair Procedure B:
Scratching detected
•
Remove front cylinder head (follow the steps above to
remove the front cylinder head, then proceed to Repair
Procedure B)
•
Replace short block
•
Replace spark plugs 1-4
•
Update PCM software
Do Repair Procedure A:
No scratching detected
P0304
•
•
•
Clean pistons 1-4
Replace piston rings 1-4
Replace spark plugs 1-4
•
Update PCM software
Do Repair Procedure B:
Scratching detected
•
Replace short block
•
Replace spark plugs 1-4
•
Update PCM software
Page 24 of 65
REPAIR PROCEDURE A
Piston Removal, Cleaning, and Ring Replacement
1. Raise the vehicle.
2. Remove the CKP sensor cover and bolts, then disconnect the CKP sensor connector.
3. Remove the torque converter case cover and the four bolts securing the oil pan to the transmission.
4. Remove all bolts securing the oil pan.
Page 25 of 65
5. Using a flat blade screwdriver, separate the oil pan from the engine block in the areas shown.
6. Remove the oil strainer and baffle plate.
Page 26 of 65
7. Remove the appropriate piston depending on diagnosis.
NOTE:
• Before removing the rod caps, use a grease pencil or suitable marking pen to mark each cap and its
corresponding connecting rod with the cylinder number it came from.
• Do not confuse the existing marking on the side of the connecting rod and rod cap with a cylinder number. They
are just manufacturing marks referring to the size of the big end of the rod.
• Installing a rod cap incorrectly will result in engine knock and/or engine failure. Remove and mark one rod
assembly at a time to make sure it is assembled correctly.
• When torquing the rod cap bolts, refer to the service information for details.
Click HERE to go to the Tech2Tech® video “Tips When Working with Fracture Rods”.
Piston Cleaning and Ring Replacement
1. Remove the piston rings from the piston using a ring expander. Be careful not to damage the piston.
2. Spray the piston head and piston ring grooves thoroughly with Honda throttle plate cleaner.
Page 27 of 65
3. While holding the piston upright in your left hand, take the piston ring groove cleaner tool in your right hand and line up
the cleaner tool guides with the second (middle) piston ring groove.
4. Press the handle on the piston ring groove cleaner tool and slide the cleaning bit onto the appropriate piston
ring grooves.
5. Once the cleaning bit is in the appropriate ring grooves of the piston, make sure the tool handle clicks into place.
NOTE: There is only one notch on the tool for the handle to engage.
Page 28 of 65
6. Hold the piston steady and rotate the tool counter-clockwise five to six times to remove any carbon deposits in the
piston ring grooves. Do not rotate the tool clockwise.
NOTE: You can watch this procedure in the Tech2Tech segment “How to Clean Piston Ring Grooves”.
7. Remove the piston groove cleaning tool and clean off the carbon from the tool bit.
8. Finish cleaning the piston with throttle plate cleaner and the nylon brush. Do not use a steel wire brush.
NOTE: Below are some examples of before and after pictures. Depending on mileage and running conditions, the
pistons will achieve different levels of cleanliness.
Page 29 of 65
9. Install the piston rings as shown.
NOTE: The first (top) ring has a 1R manufacturing mark and the second (middle) ring has an SPR manufacturing
mark. The manufacturing marks must face upward.
10. Rotate the rings in their grooves, make sure the rings do not bind.
11. Position the ring end gaps as shown.
NOTE: If the ring gaps are not positioned correctly, excessive blowby may occur.
12. Apply new engine oil to the piston, the inside of the piston ring compressor, and the cylinder bore.
NOTE: Cylinder wall honing is NOT required for this repair.
Page 30 of 65
13. Install the piston/connecting rod assembly into the cylinder bore with the arrow on top of the piston facing the timing
belt side of the engine.
NOTE: Be careful not to damage the cylinder wall when installing the piston.
14. Set the piston in the ring compressor and position the piston in the cylinder based on the rod/cap marks that were
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