Catalytic Converter - Direct Fit

This procedure covers the removal and replacement of the direct-fit catalytic converter on a 2018-2024 Honda Accord with the 1.5L turbocharged engine, including oxygen sensor handling and exhaust component reinstallation.

Warnings

Tools required

Parts

• Direct-fit catalytic converter assembly × 1 — Use OEM Honda or EPA-compliant aftermarket
• Exhaust flange gaskets × 2 — 18115-5A2-A01 or equivalent
• Exhaust flange nuts × 6 — Replace if corroded

Preparation

1. Ensure engine and exhaust system are completely cool to the touch
2. Park vehicle on level ground and set parking brake
3. Raise front of vehicle and secure on jack stands at manufacturer-specified lift points
4. Remove plastic engine undertray if equipped (multiple 10mm bolts and clips)
5. Apply penetrating oil to all exhaust flange nuts and oxygen sensor threads, allow to soak for 10-15 minutes

Procedure

1. 1

   Disconnect upstream oxygen sensor
   Locate the upstream (pre-cat) oxygen sensor on the exhaust manifold side of the catalytic converter. Disconnect the electrical connector by pressing the release tab and pulling straight out. Using a 22mm oxygen sensor socket, carefully unthread the sensor counterclockwise. If sensor is seized, apply additional penetrating oil and use a breaker bar with controlled force to avoid breaking the sensor body.
2. 2

   Disconnect downstream oxygen sensor
   Locate the downstream (post-cat) oxygen sensor on the outlet side of the catalytic converter. Disconnect the electrical connector. Using the 22mm oxygen sensor socket, remove the sensor counterclockwise. Keep sensors organized if reusing, noting their original positions.
3. 3

   Remove heat shield bolts
   If equipped with a catalytic converter heat shield, remove all mounting bolts using a 10mm socket. There are typically 3-4 bolts securing the shield. Set the heat shield aside for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
4. 4

   Support catalytic converter
   Position a floor jack with a block of wood beneath the catalytic converter to support its weight during removal. Raise jack until it just contacts the converter to prevent it from falling when fasteners are removed.
5. 5

   Remove upstream exhaust flange
   Locate the flange connection between the turbo downpipe/exhaust manifold and the catalytic converter inlet. Remove the three flange nuts (typically 14mm) using a socket and ratchet. Work around the flange in a crisscross pattern. Separate the flange connection and remove the old gasket.
6. 6

   Remove downstream exhaust flange
   Locate the flange connection between the catalytic converter outlet and the mid-pipe. Remove the three flange nuts using a 14mm socket. Work in a crisscross pattern and carefully separate the joint. Remove and discard the old gasket.
7. 7

   Remove exhaust hanger support
   Disconnect the rubber exhaust hanger from its mounting bracket by pulling the rubber grommet off the hanger stud. You may need to use a pry tool or spray lubricant to ease removal. If hanger bolts need removal, use a 12mm socket.
   Torque spec

   Hanger Bolts19 Nm (14 lb-ft)
8. 8

   Remove catalytic converter
   With all fasteners and hangers disconnected, carefully lower the jack to bring the catalytic converter down and out from under the vehicle. Maneuver it past any obstructions. Inspect the old converter for failure indications such as rattling substrate or external damage.
9. 9

   Clean flange surfaces and inspect
   Use a wire brush to thoroughly clean both exhaust flange surfaces on the turbo downpipe and mid-pipe. Remove all old gasket material, carbon buildup, and corrosion. Inspect flange faces for warping or damage. Clean oxygen sensor ports in the new catalytic converter using a wire brush.
10. 10

    Install new catalytic converter
    Position the new catalytic converter on the jack and raise into approximate position. Install new exhaust gaskets on both flanges. Align the converter with the upstream and downstream flanges, ensuring proper orientation with oxygen sensor ports accessible. Reconnect the exhaust hanger to its rubber mount.
11. 11

    Install and torque flange fasteners
    Install all flange nuts hand-tight first. Apply anti-seize compound to threads of exhaust flange bolts as specified. Starting with the upstream flange, tighten nuts in a crisscross pattern to ensure even seating. Torque all flange nuts to specification. Repeat for downstream flange connection.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
12. 12

    Install oxygen sensors
    Apply a thin coat of anti-seize compound to the threads of both oxygen sensors, being extremely careful to avoid getting any compound on the sensor tip or element. Thread sensors into their respective ports by hand to prevent cross-threading. Torque sensors to specification using the 22mm oxygen sensor socket.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
13. 13

    Reconnect oxygen sensor connectors
    Connect both oxygen sensor electrical connectors, ensuring they click securely into place. Verify wiring is routed away from hot exhaust components and moving parts. Secure any wire clips or retainers to original positions.
14. 14

    Reinstall heat shield
    If equipped, position the heat shield over the catalytic converter and install all mounting bolts. Torque bolts to specification in a crisscross pattern to ensure proper fit and vibration resistance.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

1. Remove jack from under catalytic converter
2. Reinstall plastic engine undertray with all fasteners and clips
3. Lower vehicle from jack stands
4. Clear any diagnostic trouble codes using an OBD-II scanner if check engine light was on

Verification

• Start engine and allow it to idle while listening for exhaust leaks at flange connections
• Check for visible exhaust smoke or fumes escaping from flange joints
• Verify no oxygen sensor fault codes appear after a short test drive
• Take vehicle for a 10-15 minute test drive under varied conditions to verify proper operation
• After test drive, re-inspect all flange connections for signs of leaks or loosening while engine is warm
• Monitor for check engine light and verify oxygen sensor readings are within normal range using scan tool

Related trouble codes on this vehicle

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