Catalytic Converter - Universal

This procedure covers the removal and replacement of the catalytic converter with a universal aftermarket unit on a 2016-2021 Honda Civic 1.5L Turbo, including proper cutting, welding/clamping, and oxygen sensor reinstallation.

Warnings

Tools required

Parts

• Universal catalytic converter (2.0-2.25 inch diameter) × 1 — Match inlet/outlet diameter to OEM
• Exhaust band clamps or sleeve clamps × 2 — 2.0-2.25 inch diameter
• Exhaust gasket kit × 1 — Use OEM specification
• O2 sensor (if damaged) × 1 — Use OEM specification
• Anti-seize compound × 1 — High temperature rated

Preparation

1. Park vehicle on level ground and engage parking brake. Place wheel chocks behind rear wheels
2. Allow exhaust system to cool completely (minimum 2 hours after engine shutdown)
3. Raise front of vehicle using floor jack and support securely on jack stands at manufacturer lift points
4. Spray all exhaust flange bolts, heat shield bolts, and O2 sensor with penetrating oil. Allow to soak 15-30 minutes
5. Disconnect negative battery terminal to prevent O2 sensor codes during removal
6. Measure existing catalytic converter position and pipe lengths for reference during universal converter installation

Procedure

1. 1

   Remove heat shields
   Remove the exhaust manifold heat shields by removing the heat shield mounting bolts. There are typically 3-4 bolts securing the upper heat shield. Set shields aside for reinstallation.
   Torque spec

   Heat Shield Bolts10 Nm (7 lb-ft)
2. 2

   Disconnect upstream oxygen sensor
   Locate the upstream oxygen sensor on the exhaust manifold/catalytic converter assembly. Disconnect the electrical connector by pressing the release tab. Using an O2 sensor socket or 22mm wrench, carefully unthread the sensor counterclockwise. Apply penetrating oil if sensor is seized. Inspect sensor threads and replace if damaged.
   ⚠O2 sensors are extremely fragile. Do not use excessive force or leverage that could break the sensor body.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
3. 3

   Remove exhaust flange connection
   Locate the exhaust flange where the catalytic converter/downpipe connects to the mid-pipe (typically after the catalytic converter). Remove the two flange bolts and separate the connection. Remove and discard the old exhaust gasket. Support the exhaust system with a strap or stand to prevent stress on hangers.
   Torque spec

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

   Disconnect exhaust hangers
   Locate the rubber exhaust hangers supporting the front exhaust pipe section. Using a prying tool or by hand, carefully work the exhaust pipe loops off the rubber hangers. There are typically 1-2 hangers in this section. Support the exhaust to prevent it from falling.
   Torque spec

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

   Remove turbocharger downpipe flange
   Locate the flange connection between the turbocharger outlet and the catalytic converter/downpipe. Remove the three flange bolts securing this connection. Carefully separate the flange and remove the old gasket. The entire downpipe and catalytic converter assembly can now be lowered from the vehicle.
   ⚠Downpipe assembly is heavy and awkward. Use assistance or support to prevent injury when removing.
   Torque spec

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

   Measure and mark cutting points
   With the catalytic converter/downpipe assembly removed, identify the defective catalytic converter section. Measure the universal catalytic converter inlet and outlet pipe diameters (typically 2.0-2.25 inches). Mark cut points on the existing exhaust pipe to remove the old catalytic converter while leaving sufficient straight pipe for clamping or welding the universal converter. Leave at least 2-3 inches of straight pipe before and after bends.
7. 7

   Cut out old catalytic converter
   Using a reciprocating saw with a metal cutting blade or an exhaust pipe cutter, carefully cut the exhaust pipe at the marked locations to remove the old catalytic converter. Make cuts as straight as possible for proper universal converter fitment. Clean cut edges with a wire brush or grinder to remove burrs and create a smooth mating surface.
   ⚠️Cutting metal pipe creates sharp edges and hot sparks. Wear heavy gloves and eye protection. Ensure no fuel lines or brake lines are nearby.
8. 8

   Prepare oxygen sensor bung
   The universal catalytic converter should have an O2 sensor bung welded into it. Verify the bung thread size matches the Honda O2 sensor (M18 x 1.5). If the universal converter lacks a bung in the correct position, you must have one welded in the same orientation as the original (typically 45-90 degrees from vertical before the converter substrate).
9. 9

   Install universal catalytic converter
   Position the universal catalytic converter between the cut pipe sections, ensuring proper flow direction (arrow on converter body points toward rear of vehicle). The converter substrate should face the same direction as original. Slide exhaust band clamps onto pipes before positioning converter. Overlap pipe ends into converter inlets by at least 2 inches. For permanent installation, weld the converter to pipe sections. For clamp installation, position band clamps over joints and tighten evenly to manufacturer specifications (typically 40-50 ft-lbs for band clamp bolts).
   ℹ️Welded installation provides better seal and longevity. Clamped installation allows for future removal but may develop leaks over time.
10. 10

    Reinstall downpipe assembly
    Lift the modified downpipe/catalytic converter assembly back into position under the vehicle. Install a new gasket at the turbocharger flange connection. Align the flange and hand-start all three flange bolts. Apply anti-seize to bolt threads. Torque flange bolts in a star pattern to specification.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
11. 11

    Reconnect exhaust hangers and mid-pipe
    Reattach the exhaust pipe loops to the rubber exhaust hangers. Install a new exhaust gasket at the mid-pipe flange connection. Align the flange and hand-start both flange bolts. Apply anti-seize to bolt threads. Torque flange bolts to specification ensuring proper alignment with no binding.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)

    Hanger Bolts19 Nm (14 lb-ft)
12. 12

    Install upstream oxygen sensor
    Apply a thin coat of anti-seize compound to the O2 sensor threads only (do not get anti-seize on the sensor tip). Thread the oxygen sensor into the bung on the universal catalytic converter by hand until snug. Torque the O2 sensor to specification using an O2 sensor socket. Reconnect the electrical connector ensuring it clicks securely.
    ⚠Never apply anti-seize to the O2 sensor tip or ceramic element. This will contaminate the sensor and cause false readings.
    Torque spec

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

    Reinstall heat shields
    Position the exhaust manifold heat shields back in their original locations. Install and hand-tighten all heat shield bolts. Torque heat shield bolts to specification, ensuring shields are properly seated and not vibrating against other components.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)
14. 14

    Inspect installation and lower vehicle
    Visually inspect all exhaust connections for proper alignment and clearance. Ensure no exhaust components contact the chassis, subframe, or other components. Verify all bolts are torqued and all hangers are properly engaged. Reconnect the negative battery terminal. Lower vehicle from jack stands.

Reassembly

1. Double-check all exhaust flange bolts are torqued to specification with anti-seize applied
2. Verify O2 sensor electrical connector is fully seated and secure
3. Ensure all heat shields are reinstalled to prevent heat damage to nearby components
4. Confirm exhaust system has proper clearance from chassis and suspension components throughout full suspension travel

Verification

• Start engine and listen for exhaust leaks at all connection points. A hissing sound indicates a leak requiring re-torquing or gasket replacement
• Allow engine to reach operating temperature and verify no abnormal sounds or vibrations from exhaust system
• Check for check engine light. If P0420 or P0430 codes appear immediately, verify O2 sensor is connected and universal converter is installed in correct flow direction
• Perform a test drive and monitor engine performance. Universal converters may trigger efficiency codes after several drive cycles if they do not meet OEM flow characteristics
• After 50-100 miles, re-inspect all exhaust connections and re-torque flange bolts if necessary, as exhaust gaskets may compress with heat cycling
• If using band clamps, inspect clamp tightness after first few heat cycles and re-tighten if needed

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