exhaust

Intermediate Pipe

for 2021 Honda Civic 1.5L I4 Turbo · FWD

Difficulty

Moderate

Time

1.0 h

Tools

Steps

This procedure covers the removal and replacement of the intermediate pipe on a 2016-2021 Honda Civic with the 1.5L turbocharged engine, including handling of exhaust flanges and hangers.

Warnings

⚠️The exhaust system remains extremely hot for 30-60 minutes after engine shutdown. Allow complete cooling before beginning work to avoid severe burns.

⚠Exhaust components may be corroded and brittle. Use penetrating oil and allow adequate soak time to prevent bolt breakage.

⚠Never work under a vehicle supported only by a jack. Always use jack stands rated for the vehicle weight.

ℹ️This vehicle may have one or two oxygen sensors on the intermediate pipe depending on trim level and emissions equipment.

Tools required

Floor jack and jack standsEssential

Wheel chocksEssential

10mm socket and ratchetEssential

12mm socket and ratchetEssential

14mm socket and ratchetEssential

17mm wrenchEssential

Torque wrench (10-50 Nm range)Essential

Penetrating oilEssential

Anti-seize compoundEssential

Wire brush

Rubber mallet

Pry bar

O2 sensor socket (22mm)

Parts

Intermediate pipe assembly × 1 — Use OEM Honda replacement or equivalent
Exhaust flange gaskets × 2 — Upper and lower flange gaskets
Exhaust flange bolts and nuts × 1 — Replace if corroded
Rubber exhaust hangers × 1 — Replace if torn or cracked

Preparation

Ensure the exhaust system is completely cold to the touch
Park vehicle on level ground and engage parking brake
Place wheel chocks behind rear wheels
Raise the front of the vehicle using a floor jack at the designated front jacking point
Support vehicle securely on jack stands placed at the manufacturer-specified points on the pinch welds
Spray all exhaust flange bolts, hanger bolts, and oxygen sensor threads with penetrating oil and allow to soak for 15-30 minutes

Procedure

1
Disconnect oxygen sensor electrical connector
Locate the oxygen sensor electrical connector on the intermediate pipe. Press the locking tab and disconnect the wiring harness. If removing the sensor, use a 22mm O2 sensor socket or wrench to unthread it counterclockwise, being careful not to damage the threads in the exhaust pipe.
2
Remove heat shield if equipped
If a heat shield is present over the intermediate pipe, remove the mounting bolts using a 10mm socket. Set the heat shield aside for reinstallation. Clean any rust or debris from the mounting points.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)
3
Support the exhaust system
Position a jack stand or wooden block under the muffler assembly to support the weight of the rear exhaust section once the intermediate pipe is disconnected. This prevents strain on downstream components.
4
Disconnect upstream flange from catalytic converter
Using a 14mm socket and wrench, remove the two or three flange bolts connecting the intermediate pipe to the catalytic converter outlet flange. You may need one tool to hold the nut while turning the bolt. Separate the flange connection and remove the old gasket.
⚠If bolts are severely corroded and cannot be removed, carefully apply heat with a torch or consider cutting the bolts with a reciprocating saw.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
5
Disconnect downstream flange
Locate the flange connection between the intermediate pipe and the rear exhaust section. Remove the flange bolts using a 14mm socket and wrench. Separate the flange and discard the old gasket.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
6
Remove exhaust hanger connections
The intermediate pipe is supported by rubber exhaust hangers. Using a pry bar or by hand, carefully work the pipe mounting tabs out of the rubber hangers. A spray of soapy water can help lubricate stubborn hangers. Note the orientation of each hanger for reassembly.
7
Remove intermediate pipe
With all connections disconnected, carefully lower and maneuver the intermediate pipe out from under the vehicle. You may need to rotate or angle the pipe to clear chassis components and suspension parts.
8
Clean flange surfaces and inspect components
Use a wire brush to thoroughly clean the catalytic converter outlet flange and rear exhaust inlet flange surfaces, removing all old gasket material and carbon deposits. Inspect the flanges for cracks or warping. Check rubber exhaust hangers for tears or deterioration and replace if necessary.
9
Install oxygen sensor in new pipe if removed
If the oxygen sensor was removed, apply a thin coat of anti-seize compound to the threads only (do not get anti-seize on the sensor tip). Thread the sensor into the new intermediate pipe by hand, then tighten using an O2 sensor socket.
⚠Apply anti-seize only to the threads, never to the sensor element. Contamination of the sensor will cause failure and check engine lights.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
10
Position new intermediate pipe and attach hangers
Maneuver the new intermediate pipe into position under the vehicle. Align the mounting tabs with the rubber exhaust hangers and press firmly to seat them. A rubber mallet can help tap the tabs into place. Ensure the pipe is properly supported before connecting flanges.
11
Install new gasket and connect upstream flange
Place a new exhaust gasket on the catalytic converter outlet flange. Position the intermediate pipe flange against it and start all flange bolts by hand. Apply anti-seize compound to the bolt threads. Tighten bolts in a cross pattern to the specified torque.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
12
Install new gasket and connect downstream flange
Install a new exhaust gasket at the connection between the intermediate pipe and rear exhaust section. Align the flanges and start all bolts by hand. Tighten the flange bolts in a cross pattern to the specified torque.
Torque spec
Exhaust Flange Bolts45 Nm (33 lb-ft)
13
Reinstall heat shield
If a heat shield was removed, position it over the intermediate pipe and install the mounting bolts. Tighten to the specified torque using a 10mm socket.
Torque spec
Heat Shield Bolts10 Nm (7 lb-ft)
14
Reconnect oxygen sensor
Connect the oxygen sensor electrical connector to the wiring harness, ensuring the locking tab clicks into place securely. Verify the wire routing does not contact hot exhaust components or moving suspension parts.

Reassembly

Verify all exhaust flange bolts are torqued to specification and no connections were missed
Ensure all rubber exhaust hangers are properly seated and supporting the pipe
Check that no wiring or brake lines are in contact with the new intermediate pipe
Remove jack stands and lower vehicle to the ground

Verification

Start the engine and listen for exhaust leaks at both flange connections. A hissing sound indicates a leak requiring retightening or gasket replacement
With the engine running, visually inspect all connections for escaping exhaust gases
Allow the engine to reach operating temperature and recheck for leaks
Take a short test drive and verify no unusual exhaust noises or vibrations are present
If an oxygen sensor was removed and reinstalled, verify no check engine light illuminates after several drive cycles