Catalytic Converter - Universal

This procedure covers the removal and replacement of a failed catalytic converter with a universal aftermarket unit on a 2018-2024 Honda Accord 1.5L Turbo, including exhaust disassembly, welding/clamping the universal converter, and oxygen sensor reinstallation.

Warnings

Tools required

Parts

• Universal catalytic converter (2.0" inlet/outlet, 10-14" length) × 1 — Match OEM converter diameter and cell count for emissions compliance
• Exhaust pipe adapter sleeves (if not welding) × 2 — 2.0" diameter, stainless steel
• Heavy-duty exhaust clamps × 2 — 2.0" band clamps, stainless steel
• Exhaust flange gaskets × 2 — Honda OEM 18229-5A2-A01 or equivalent
• Exhaust hanger isolators (if damaged) × 2 — Honda OEM 18215-TR3-A01

Preparation

1. Park vehicle on level surface and allow exhaust system to cool completely (minimum 2 hours after last operation)
2. Disconnect negative battery terminal to prevent CEL codes during O2 sensor disconnection
3. Raise vehicle with floor jack and support securely on jack stands at manufacturer lift points (minimum 18 inches clearance recommended)
4. Apply penetrating oil to all exhaust flange bolts, hanger bolts, and oxygen sensor threads. Allow to soak 15-30 minutes
5. Locate both oxygen sensors on the catalytic converter (upstream near engine, downstream near rear of converter)
6. Take photos of exhaust routing and hanger positions for reference during reinstallation

Procedure

1. 1

   Disconnect oxygen sensors
   Locate the upstream O2 sensor electrical connector near the engine bay and the downstream connector near the transmission tunnel. Press the release tab and disconnect both connectors. Using a 22mm oxygen sensor socket, carefully remove both O2 sensors from the catalytic converter by turning counterclockwise. If sensors are seized, apply heat with heat gun (not torch directly on sensor) to exhaust bung area, then retry removal.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
2. 2

   Remove heat shields
   Remove all heat shield bolts securing the upper and lower catalytic converter heat shields using a 10mm socket. There are typically 4-6 bolts total. Set heat shields aside for reinstallation. Inspect heat shields for damage or excessive corrosion; replace if necessary.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
3. 3

   Disconnect front exhaust flange
   Locate the exhaust flange connection between the turbo downpipe and catalytic converter inlet. Remove the two 14mm flange bolts and separate the flange connection. You may need to apply penetrating oil and use gentle prying to break the seal. Remove and discard the old flange gasket.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
4. 4

   Support exhaust and remove hanger connections
   Place a floor jack or exhaust support stand under the catalytic converter assembly. Using a 12mm socket, remove the hanger bolts connecting the exhaust hangers to the rubber isolators. There are typically 2-3 hanger points. Carefully twist and pull exhaust hangers from rubber isolators if bolts are captive to exhaust pipe.
   Torque spec

   Hanger Bolts19 Nm (14 lb-ft)
5. 5

   Disconnect rear exhaust flange
   Locate the exhaust flange connection between the catalytic converter outlet and the mid-pipe/resonator. Remove the two 14mm flange bolts. Separate the flange and remove the old gasket. Lower the catalytic converter assembly carefully from the vehicle.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
6. 6

   Measure and mark cut locations
   Place the old catalytic converter next to the universal unit to determine proper placement. Measure the distance from the inlet flange to where the universal converter will begin, and from the outlet flange to where it will end. Allow 2-3 inches of straight pipe on each side of the universal converter for proper fitment with adapters or welds. Mark cut locations on the old exhaust pipe with a metal scribe or marker.
   ℹ️Ensure the universal converter is positioned to maintain proper ground clearance and avoid contact with undercarriage components or heat-sensitive parts.
7. 7

   Cut out old catalytic converter
   Using a reciprocating saw with metal cutting blade or an angle grinder with cutoff wheel, carefully cut the exhaust pipe at both marked locations to remove the old catalytic converter. Make cuts as square and clean as possible. Use an exhaust pipe cutter for cleaner, more precise cuts if available. Clean cut edges with a wire brush to remove burrs and debris.
   ⚠️Wear safety glasses and hearing protection. Cutting will produce hot metal sparks and loud noise. Ensure no flammable materials are nearby.
8. 8

   Prepare universal converter installation
   Clean the inside and outside of the remaining exhaust pipe sections thoroughly with a wire brush. Test-fit the universal catalytic converter with adapter sleeves (if using clamp method) or verify proper alignment for welding. The converter should be positioned with directional arrow (if marked) pointing toward rear of vehicle. Ensure inlet and outlet pipes slide together with minimal gap (less than 1/8 inch).
   ℹ️Universal converters may have directional flow indicators. Verify proper orientation before permanent installation.
9. 9

   Install universal catalytic converter
   If welding: Position the universal converter with proper alignment and tack weld in 3-4 spots around each joint. Verify alignment, then complete full circumference welds on both inlet and outlet connections. Allow welds to cool naturally. If using clamps: Slide adapter sleeves over joints, position universal converter, and install heavy-duty band clamps over each connection. Tighten clamps evenly in a cross pattern to manufacturer specifications (typically 40-50 ft-lbs).
   ⚠️Welding produces intense UV light, heat, and fumes. Use proper welding helmet, gloves, and ventilation. Clear area of all flammable materials.
10. 10

    Drill and install oxygen sensor bungs
    The universal converter should have pre-welded O2 sensor bungs or require bung installation. Position the upstream bung approximately 6-8 inches from the converter inlet and the downstream bung 6-8 inches from the outlet, both at approximately 10 o'clock position when viewing from rear. If bungs need welding, weld securely ensuring full penetration. Clean threads with a thread chaser and apply anti-seize to O2 sensor threads (threads only, not sensor tip).
    ⚠Oxygen sensor bung placement is critical for proper engine management system function. Incorrect placement may cause check engine lights or poor performance.
11. 11

    Reinstall exhaust assembly
    Raise the completed exhaust assembly into position using a floor jack. Align the front flange with the turbo downpipe connection and install a new flange gasket. Start both flange bolts by hand. Align the rear flange with the mid-pipe connection, install new gasket, and start those bolts by hand. Do not fully tighten yet.
    Torque spec

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

    Connect exhaust hangers and align system
    Reconnect all exhaust hangers to their rubber isolators or reinstall hanger bolts. Ensure the exhaust system hangs naturally without binding or stress. Check clearance around all components, ensuring minimum 1-inch clearance from undercarriage, fuel lines, brake lines, and wiring. Adjust hanger positions as needed for proper alignment.
    Torque spec

    Hanger Bolts19 Nm (14 lb-ft)
13. 13

    Torque all exhaust connections
    Apply anti-seize compound to exhaust flange bolt threads. Torque the front exhaust flange bolts (turbo to converter) to 45 Nm (33 lb-ft) in a cross pattern. Torque the rear flange bolts (converter to mid-pipe) to 45 Nm (33 lb-ft) in a cross pattern. Torque all hanger bolts to 19 Nm (14 lb-ft). Verify all connections are secure and properly seated.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)

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

    Install oxygen sensors
    Apply a thin coat of anti-seize compound to the threads of both oxygen sensors (threads only, avoid contaminating the sensor tip). Thread each O2 sensor into its respective bung by hand first to avoid cross-threading. Using the oxygen sensor socket, torque both sensors to 45 Nm (33 lb-ft). Reconnect both O2 sensor electrical connectors, ensuring they click securely into place.
    Torque spec

    O2 Sensor45 Nm (33 lb-ft)
15. 15

    Reinstall heat shields
    Position the heat shields over the catalytic converter area. Install all heat shield bolts and torque to 10 Nm (7 lb-ft). Ensure heat shields do not contact the exhaust pipe and have proper clearance for thermal expansion.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

1. Reconnect the negative battery terminal
2. Lower the vehicle from jack stands
3. Perform a final visual inspection of all connections, ensuring no tools or materials were left in the engine bay or under the vehicle

Verification

• Start the engine and listen for exhaust leaks at all connection points. Any hissing or ticking sounds indicate a leak requiring immediate attention
• Allow the engine to reach operating temperature while monitoring for unusual sounds or smells
• Check for exhaust leaks using a safe method (listening for hissing, visual smoke inspection). Do NOT use hands near hot exhaust
• Use an OBD-II scanner to verify no diagnostic trouble codes are present. Clear any codes stored during the procedure
• Perform a test drive and monitor engine performance. The check engine light should remain off after 1-2 complete drive cycles
• After the first 50-100 miles, re-inspect all clamp connections (if used) and re-tighten if necessary. Welds should not require re-inspection
• Monitor O2 sensor readiness status with OBD-II scanner. All monitors should complete within 2-3 drive cycles if installation was successful

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