This procedure covers removal and installation of the front exhaust pipe (downpipe) on the 2018-2024 Honda Accord 1.5L Turbo, including oxygen sensor handling and heat shield removal.

Warnings

Tools required

Parts

• Front exhaust pipe gasket (turbo to front pipe) × 1 — 18115-6AA-A00
• Front pipe to catalytic converter gasket × 1 — 18229-6AA-A00
• Exhaust flange bolts × 6 — Use OEM specification
• Anti-seize compound × 1 — Use high-temperature rated

Preparation

1. Ensure engine and exhaust system are completely cool to the touch
2. Raise vehicle securely on jack stands with adequate working clearance
3. Spray all exhaust flange bolts, oxygen sensor, and hanger bolts with penetrating oil and allow 15-30 minutes soak time
4. Disconnect negative battery terminal if working near oxygen sensor wiring connectors
5. Remove engine under cover if equipped

Procedure

1. 1

   Disconnect oxygen sensors
   Locate the upstream oxygen sensor on the front pipe near the turbo outlet and the downstream sensor before the catalytic converter. Disconnect both electrical connectors by pressing the release tab and pulling straight out. Carefully unclip wiring harness from any retaining clips along the front pipe.
2. 2

   Remove heat shield
   Using a 10mm socket, remove all heat shield bolts securing the front pipe heat shield. Note bolt locations as some models have multiple shield sections. Remove heat shield and set aside.
   Torque spec

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

   Remove upstream oxygen sensor
   Using a 22mm oxygen sensor socket, carefully remove the upstream oxygen sensor from the front pipe. Turn counterclockwise and remove completely. Protect sensor tip from damage if reusing. Inspect threads in front pipe bung for damage.
   ⚠Do not use regular socket which can damage oxygen sensor wiring. Always use dedicated oxygen sensor socket with wire cutout.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
4. 4

   Remove downstream oxygen sensor
   Using the same 22mm oxygen sensor socket, remove the downstream oxygen sensor from the front pipe. This sensor may be more difficult to access. Turn counterclockwise and remove completely. Protect sensor if reusing.
   Torque spec

   O2 Sensor45 Nm (33 lb-ft)
5. 5

   Separate turbo-to-front pipe connection
   Locate the 3-bolt flange connecting the turbocharger outlet to the front pipe. Using a 14mm socket, remove all three exhaust flange bolts. The connection is at the top front of the front pipe. If bolts are severely seized, apply heat carefully with propane torch while protecting nearby components.
   ⚠These bolts often seize from heat cycling. Do not force and risk breaking bolts off in turbo flange. Use penetrating oil and patience.
   Torque spec

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

   Support front pipe
   Position a jack or support under the front pipe and catalytic converter assembly to prevent it from dropping when hangers are disconnected. The assembly is heavy and must be supported safely.
7. 7

   Disconnect exhaust hangers
   Using a 12mm socket, remove the hanger bolts securing rubber hangers that support the front pipe. Typically there are 2-3 hangers along the length. Alternatively, if hangers are rubber isolator style, use exhaust hanger tool or pry carefully to pop hangers off their mounts.
   Torque spec

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

   Separate front pipe from catalytic converter
   Using a 14mm socket, remove the three bolts at the flange connection between the front pipe and catalytic converter. This is typically a spring-loaded flange connection. Once bolts are removed, separate the connection and carefully lower the front pipe from the vehicle.
   Torque spec

   Exhaust Flange Bolts45 Nm (33 lb-ft)
9. 9

   Clean mating surfaces
   With front pipe removed, thoroughly clean all flange mating surfaces on both the turbocharger outlet and catalytic converter inlet using a wire brush or scraper. Remove all old gasket material and carbon buildup to ensure proper sealing. Inspect flanges for warping or cracks.
10. 10

    Install new gaskets and position front pipe
    Install new gasket at turbo outlet flange and catalytic converter inlet flange. Position new front pipe into place, aligning both flanges. Support pipe with jack while aligning. Ensure oxygen sensor bungs are accessible and face correct direction.
11. 11

    Install and torque turbo flange connection
    Apply anti-seize compound to threads of new exhaust flange bolts. Hand-start all three bolts at the turbo-to-front pipe flange. Tighten bolts in a cross pattern to ensure even seating, then torque to specification using torque wrench.
    Torque spec

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

    Install and torque catalytic converter flange
    Hand-start all three flange bolts at the front pipe-to-catalytic converter connection. Tighten in cross pattern, then torque to specification. Ensure gasket remains properly seated during tightening.
    Torque spec

    Exhaust Flange Bolts45 Nm (33 lb-ft)
13. 13

    Reconnect exhaust hangers
    Align rubber hangers with their mounting points and secure with hanger bolts. Torque hanger bolts to specification. Ensure exhaust system hangs properly with adequate clearance from chassis, heat shields, and fuel lines.
    Torque spec

    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 only - keep anti-seize away from sensor tips. Thread both oxygen sensors into their bungs hand-tight first to prevent cross-threading, then torque to specification using 22mm oxygen sensor socket and torque wrench.
    ⚠Never apply anti-seize to oxygen sensor tip. Apply only to threads. Contamination of sensor tip will cause immediate sensor failure.
    Torque spec

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

    Reinstall heat shield and reconnect sensors
    Position heat shield over front pipe and secure with original bolts, torquing to specification. Reconnect both oxygen sensor electrical connectors ensuring they click firmly into place. Secure wiring harness to all retaining clips to prevent contact with exhaust or moving components.
    Torque spec

    Heat Shield Bolts10 Nm (7 lb-ft)

Reassembly

1. Reinstall engine under cover if equipped
2. Reconnect negative battery terminal if disconnected
3. Lower vehicle from jack stands carefully
4. Double-check all electrical connections are secure and wiring is properly routed away from hot exhaust components

Verification

• Start engine and allow to idle while listening for exhaust leaks at both flange connections - any ticking or hissing indicates leak requiring attention
• Check for oxygen sensor fault codes using OBD-II scanner - clear any codes that were set during battery disconnect and verify no new codes appear
• Perform brief test drive and re-check all connections for leaks after exhaust reaches operating temperature
• Verify oxygen sensor readings are within normal range using scan tool (upstream sensor should fluctuate rapidly, downstream should be relatively steady)
• Inspect heat shields for proper fitment and ensure no rattling or contact with chassis

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