exhaust

Catalytic Converter - California

for 2021 Honda Accord 1.5L I4 Turbo · FWD

Difficulty

Moderate

Time

1.5 h

Tools

Steps

✓Fact-checked. Built from OLP's spec database, then independently fact-checked line by line with every correction applied. Master-tech sign-off by Chris Hackleman is queued. Cross-check torque values against the factory manual, and stop if anything looks unsafe. How our data is made.

This procedure replaces the California-specification catalytic converter on a 2018-2024 Honda Accord with 1.5L turbo engine, including removal and installation of oxygen sensors and exhaust components.

Warnings

⚠️Exhaust components remain extremely hot for over an hour after engine shutdown. Allow complete cooling before beginning work to avoid severe burns.

⚠California catalytic converters must meet CARB specifications. Ensure replacement part is California-compliant and properly certified.

⚠Oxygen sensor threads are easily damaged. Use proper oxygen sensor socket and do not cross-thread during installation.

ℹ️Exhaust fasteners are prone to corrosion. Apply penetrating oil 30 minutes before starting if vehicle has high mileage or rust.

Tools required

Floor jack and jack standsEssential

Wheel chocksEssential

Torque wrench (10-50 Nm range)Essential

22mm oxygen sensor socketEssential

14mm socket and ratchetEssential

10mm socket and ratchet

Penetrating oil

Anti-seize compoundEssential

Wire brush

Exhaust hangers removal tool or pry bar

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

Parts

California-specification catalytic converter assembly × 1 — Honda OEM California CARB-compliant part
Exhaust flange gasket × 2 — Use OEM specification
Primary oxygen sensor (if reusing, inspect condition) × 1 — 18213-5AA-A01
Secondary oxygen sensor (if reusing, inspect condition) × 1 — 18213-5BA-A01

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 cool to the touch
Park vehicle on level surface, apply parking brake, and place wheel chocks behind rear wheels
Raise front of vehicle using floor jack and support securely on jack stands at manufacturer-specified lift points
Disconnect negative battery terminal to prevent oxygen sensor codes during removal
If fasteners show corrosion, spray all exhaust flange bolts and oxygen sensors with penetrating oil and wait 30 minutes

Procedure

1
Remove heat shields
Locate and remove the heat shield bolts covering the catalytic converter area. The 1.5L turbo has a primary heat shield over the turbocharger and catalytic converter. Remove all heat shield bolts and carefully set shields aside.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)
2
Disconnect primary oxygen sensor
Locate the primary (upstream) oxygen sensor in the exhaust manifold before the catalytic converter. Disconnect the electrical connector by pressing the release tab. Using a 22mm oxygen sensor socket, carefully unthread the sensor counterclockwise. Inspect sensor condition and threads.
⚠Do not allow oxygen sensor to hang by wiring harness. Support sensor to prevent wire damage.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
3
Disconnect secondary oxygen sensor
Locate the secondary (downstream) oxygen sensor after the catalytic converter. Disconnect the electrical connector. Using the oxygen sensor socket, remove the sensor counterclockwise. Inspect threads and sensor condition for reuse or replacement.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
4
Remove upstream exhaust flange connection
Locate the exhaust flange bolts connecting the catalytic converter to the turbocharger outlet. Remove the two 14mm flange bolts. Separate the connection and remove the old gasket. Support the catalytic converter to prevent it from dropping.
⚠Support catalytic converter weight before removing all fasteners to prevent component damage or injury.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
5
Remove downstream exhaust flange connection
Locate the flange bolts connecting the catalytic converter outlet to the mid-pipe. Remove the two 14mm flange bolts. Keep these bolts separate as they will be reused.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
6
Disconnect exhaust hangers
Locate the rubber exhaust hangers supporting the catalytic converter assembly. Using a pry bar or exhaust hanger tool, carefully work each rubber hanger off its mounting bracket. There are typically 1-2 hangers on this section.
Torque spec
Hanger Bolts19 Nm (14 lb-ft)
7
Remove catalytic converter assembly
With all connections and hangers disconnected, carefully lower and remove the catalytic converter assembly from the vehicle. Maneuver past subframe and suspension components as needed. Inspect mounting points and flanges for damage.
8
Clean flange surfaces and inspect
Use a wire brush to thoroughly clean both exhaust flange surfaces on the turbocharger outlet and mid-pipe connection. Remove all old gasket material, carbon buildup, and corrosion. Inspect flange surfaces for warping or cracks that could cause leaks.
9
Prepare new catalytic converter
Unpack the new California-specification catalytic converter and verify it matches the OEM configuration. Apply anti-seize compound to oxygen sensor threads only (not the sensor tip). Install both oxygen sensors hand-tight into the new catalytic converter.
⚠Never apply anti-seize to oxygen sensor tips as this will contaminate the sensor and cause false readings.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
10
Install new catalytic converter
Position the new catalytic converter assembly into place, maneuvering past subframe components. Align with both upstream and downstream flange connections. Reconnect exhaust hangers to their rubber mounts, ensuring proper alignment before tightening any bolts.
11
Install new flange gaskets and connect upstream flange
Place a new exhaust flange gasket between the turbocharger outlet and catalytic converter inlet. Insert flange bolts and hand-tighten. Apply anti-seize to bolt threads. Torque bolts in a crossing pattern to specification.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
12
Connect downstream flange
Install new gasket at the catalytic converter outlet to mid-pipe connection. Insert flange bolts and hand-tighten. Apply anti-seize to threads. Torque bolts in a crossing pattern to specification. Verify proper alignment of entire exhaust system.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
13
Torque oxygen sensors
Using the torque wrench and oxygen sensor socket, torque both primary and secondary oxygen sensors to specification. Do not over-torque as this can damage threads in the catalytic converter. Reconnect both oxygen sensor electrical connectors, ensuring they click securely into place.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
14
Reinstall heat shields
Position heat shields back over the catalytic converter and turbocharger area. Install all heat shield bolts and torque to specification. Ensure shields are properly seated and do not contact moving components.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

Reconnect negative battery terminal
Lower vehicle from jack stands carefully
Double-check all connections are secure and no tools were left in engine bay

Verification

Start engine and allow to idle. Listen for any exhaust leaks at flange connections (hissing or ticking sounds indicate leak)
Check for exhaust odors in cabin which would indicate flange leak
Verify no check engine light appears after 2-3 drive cycles (oxygen sensor codes may require drive cycle to clear)
Use a scan tool to verify both oxygen sensors are reading properly and switching appropriately
Perform visual inspection under vehicle for any exhaust leaks, loose hangers, or heat shield rattles
Confirm catalytic converter monitoring system shows readiness after sufficient drive time (may take 50-100 miles)