exhaust

Catalytic Converter - California

for 2017 Honda Civic 1.5L I4 Turbo · FWD

Editorial review:Chris Hackleman — Master Technician · 20+ years

Difficulty

Moderate

Time

1.5 h

Tools

Steps

✓Expert-verified. Personally reviewed and approved by OLP's master technicians (Chris Hackleman — 20+ years each). Always follow the vehicle's factory service information and torque specs.

Replace the California-spec catalytic converter assembly on a 2016-2021 Honda Civic with 1.5L turbo engine, including oxygen sensor transfer and exhaust system reconnection.

Warnings

⚠️Allow exhaust system to cool completely before beginning work. Catalytic converter can remain hot for over an hour after engine shutdown and can cause severe burns.

⚠Exhaust fasteners may be corroded or seized. Apply penetrating oil 30 minutes before removal to prevent bolt breakage.

⚠California requires CARB-certified replacement catalytic converters with valid Executive Order (EO) numbers. Non-compliant parts may result in failed emissions inspection and legal penalties.

ℹ️O2 sensors are fragile. Do not drop or impact sensors during removal and handle connectors carefully.

Tools required

Floor jack and jack standsEssential

Torque wrench (10-50 Nm range)Essential

O2 sensor socket or 22mm wrenchEssential

12mm socket and ratchetEssential

14mm socket and ratchetEssential

Extension bars (6-inch and 12-inch)Essential

Penetrating oil

Anti-seize compoundEssential

Wire brush

Shop towels

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Parts

Catalytic converter assembly (California-spec CARB certified) × 1 — Must be CARB-compliant for California, verify EO number
Exhaust gasket (turbo to catalytic converter) × 1 — 18115-5AA-A00 or equivalent
Exhaust gasket (catalytic converter to mid-pipe) × 1 — 18115-5AA-A01 or equivalent
Heat shield mounting hardware × 1 — Use OEM specification

As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.

Preparation

Ensure engine and exhaust system are completely cold to the touch
Park vehicle on level surface and engage parking brake
Raise front of vehicle and support securely on jack stands rated for vehicle weight
Spray all exhaust flange bolts, O2 sensor, and heat shield bolts with penetrating oil and allow to soak for 30 minutes
Disconnect negative battery terminal to prevent O2 sensor fault codes during replacement

Procedure

1
Remove heat shield
Locate the catalytic converter heat shield. Remove the heat shield mounting bolts using a 12mm socket. There are typically 3-4 bolts securing the shield. Remove the heat shield and set aside for reinstallation.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)
2
Disconnect upstream oxygen sensor
Locate the upstream O2 sensor mounted in the turbocharger or front of catalytic converter. Disconnect the electrical connector by pressing the release tab and pulling straight apart. Using an O2 sensor socket or 22mm wrench, unthread the sensor counterclockwise. Remove sensor completely from exhaust.
⚠Do not use excessive force on O2 sensor. If seized, apply heat and additional penetrating oil to avoid breaking sensor in manifold.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
3
Disconnect downstream oxygen sensor
Locate the downstream O2 sensor in the rear of the catalytic converter assembly. Disconnect the electrical connector. Use O2 sensor socket or 22mm wrench to remove the sensor counterclockwise. Keep sensors organized for reinstallation.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
4
Disconnect exhaust hanger brackets
Locate the rubber exhaust hangers supporting the catalytic converter assembly. Use a 14mm socket to remove the hanger bracket bolts. Support the catalytic converter with one hand or have an assistant hold it to prevent it from dropping when unbolted.
Torque spec
Hanger Bolts19 Nm (14 lb-ft)
5
Remove upstream exhaust flange
Locate the exhaust flange connection between the turbocharger outlet and catalytic converter inlet. Remove the two flange bolts using a 14mm socket and extension. The exhaust may need to be supported to prevent binding. Separate the flange connection and remove the old gasket.
⚠Flange bolts may be severely corroded. If bolt heads begin to round, use a 6-point socket and apply additional penetrating oil.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
6
Remove downstream exhaust flange
Locate the exhaust flange connection between the catalytic converter outlet and the mid-pipe. Remove the two flange bolts using a 14mm socket. Gently separate the connection and remove the old gasket. Lower the catalytic converter assembly from the vehicle.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
7
Clean mating surfaces
Use a wire brush to thoroughly clean the flange mating surfaces on both the turbocharger outlet pipe and mid-pipe. Remove all carbon deposits, old gasket material, and corrosion to ensure proper sealing. Inspect flanges for cracks or damage.
ℹ️Damaged or warped flanges will cause exhaust leaks regardless of new gaskets. Inspect carefully before proceeding.
8
Prepare new catalytic converter
Verify the new catalytic converter is CARB-certified for California and matches the original configuration. Apply anti-seize compound to the O2 sensor threads only, avoiding the sensor tip. Install both O2 sensors finger-tight into the new catalytic converter.
⚠Never apply anti-seize to O2 sensor tips as this will contaminate the sensor and cause false readings.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
9
Install new catalytic converter
Position new exhaust gasket on the turbocharger outlet flange, then lift the new catalytic converter assembly into position. Align the upstream flange first and start both flange bolts finger-tight. Position the downstream gasket and align the mid-pipe flange, starting those bolts finger-tight as well.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
10
Torque exhaust flanges
Apply anti-seize to the threads of all flange bolts. Torque the upstream flange bolts (turbo to catalytic converter) to specification in a crossing pattern. Then torque the downstream flange bolts (catalytic converter to mid-pipe) to specification in a crossing pattern. Verify all connections are properly seated.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
11
Install exhaust hangers
Align the catalytic converter assembly with the rubber exhaust hangers. Install the hanger bracket bolts and torque to specification. Ensure the exhaust system hangs naturally without binding or stress on any connection points.
Torque spec
Hanger Bolts19 Nm (14 lb-ft)
12
Torque oxygen sensors
Using the O2 sensor socket or 22mm wrench, torque both the upstream and downstream oxygen sensors to specification. Reconnect both O2 sensor electrical connectors, ensuring they click securely into place and are routed away from heat sources.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
13
Reinstall heat shield
Position the heat shield over the catalytic converter assembly. Install all heat shield mounting bolts and torque to specification. Ensure the shield does not contact any part of the exhaust or make rattling noises when shaken.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

Reconnect negative battery terminal
Lower vehicle from jack stands
Start engine and listen for exhaust leaks at all flange connections
Allow engine to reach operating temperature and verify no unusual noises or smells

Verification

Visually inspect all exhaust connections for signs of leaks (soot deposits or visible gaps)
Listen for exhaust leaks at idle and during light acceleration
Use a scan tool to verify both O2 sensors are reading properly and no diagnostic trouble codes are present
Check that heat shield is secure and not rattling
Verify catalytic converter CARB certification label is visible for future emissions inspections