exhaust

O2 Sensor - Upstream

for 2021 Honda Accord 1.5L I4 Turbo · FWD

Difficulty

Easy

Time

30 min

Tools

Steps

This procedure covers the removal and replacement of the upstream oxygen (O2) sensor on the 2018-2024 Honda Accord 1.5L I4 Turbo engine.

Warnings

⚠️Perform this work only when the exhaust system is completely cool. The exhaust can cause severe burns for up to 2 hours after engine shutdown.

⚠Never apply anti-seize to the sensor body or element, only to the threads. Contamination will damage the sensor.

⚠Do not drop or handle the sensor roughly. The internal element is fragile and damage will cause improper readings.

ℹ️The upstream O2 sensor (also called Air-Fuel Ratio sensor) is located in the exhaust manifold or downpipe before the catalytic converter.

Tools required

O2 sensor socket (22mm or 7/8")Essential

3/8" ratchet with extensionEssential

Jack and jack standsEssential

Wire brush

Anti-seize compoundEssential

Penetrating oil

Torque wrenchEssential

Parts

Upstream O2 sensor (Air-Fuel Ratio Sensor) × 1 — Honda OEM 36531-5AA-A01 or equivalent

Preparation

Ensure the engine and exhaust system are completely cold to the touch
Park the vehicle on a level surface and engage the parking brake
Raise the front of the vehicle using a jack and secure it on jack stands
Remove the engine undercover if equipped to access the exhaust system
Locate the upstream O2 sensor on the exhaust manifold or front exhaust pipe (it will have a wiring harness connector)

Procedure

1
Disconnect the O2 sensor electrical connector
Trace the O2 sensor wire to its connector, which is typically secured to a bracket on the engine or chassis. Press the release tab and carefully disconnect the electrical connector. If the connector is difficult to separate, gently wiggle it while pulling to avoid breaking the locking tab.
2
Free the sensor wiring harness
Release any clips or ties securing the O2 sensor wiring to the engine or chassis. Ensure the wire has enough slack to allow sensor rotation during removal. Take note of the wire routing for reinstallation.
3
Apply penetrating oil (if needed)
If the vehicle has high mileage or the sensor has been in place for an extended period, spray penetrating oil around the sensor threads where it enters the exhaust. Allow it to soak for 5-10 minutes. This step is optional but helps prevent thread damage during removal.
⚠Keep penetrating oil away from the sensor element itself. Only apply to the threaded area at the exhaust pipe.
4
Remove the old O2 sensor
Using a 22mm O2 sensor socket and ratchet with extension, turn the sensor counterclockwise to remove it. The sensor socket has a slot to allow the wire to pass through. Apply steady pressure; if the sensor is seized, do not force it excessively as this can damage the exhaust threads. The sensor should turn with moderate effort once broken loose.
5
Inspect and clean the threads
Once the old sensor is removed, inspect the threads in the exhaust pipe for damage or excessive carbon buildup. Use a wire brush to clean the threads if necessary. Check that the threads are intact and not stripped or cross-threaded.
6
Prepare the new O2 sensor
Remove the new O2 sensor from its packaging. Apply a thin coat of anti-seize compound to the sensor threads only, being extremely careful not to get any on the sensor tip or element. The sensor may come with anti-seize pre-applied; check the manufacturer's instructions.
⚠Anti-seize must only be applied to the threads. Any contamination of the sensor element will cause permanent damage and false readings.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
7
Install the new O2 sensor
Thread the new O2 sensor into the exhaust pipe by hand, ensuring it starts straight to avoid cross-threading. Hand-tighten the sensor until it seats, then use the O2 sensor socket and torque wrench to tighten to 45 Nm (33 lb-ft). Do not over-tighten as this can damage the sensor or exhaust threads.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
8
Route and secure the wiring
Route the O2 sensor wiring following the same path as the original sensor, ensuring it does not contact hot exhaust components or moving parts. Secure the wire with any clips or ties that were removed during disassembly. Maintain proper clearance from the exhaust manifold and other heat sources.
9
Reconnect the electrical connector
Plug the O2 sensor electrical connector back together until you hear or feel a positive click. Gently tug on the connection to verify it is fully seated and locked. Ensure the connector is properly secured to its mounting bracket.
10
Reinstall undercover and lower vehicle
Reinstall the engine undercover if it was removed. Carefully lower the vehicle from the jack stands and remove the stands. Lower the vehicle completely to the ground.

Reassembly

Ensure all electrical connections are secure and properly routed away from hot exhaust components
Verify the engine undercover is properly installed with all clips and fasteners secure

Verification

Start the engine and verify the check engine light (MIL) is off or goes out after a short drive cycle
Use an OBD-II scanner to confirm there are no O2 sensor-related fault codes stored
Monitor the O2 sensor data using a scan tool to verify the sensor is providing proper voltage readings (should fluctuate for downstream or show steady readings for upstream A/F sensor)
Check for exhaust leaks around the sensor installation point while the engine is running
Perform a test drive and verify the vehicle runs smoothly without hesitation or rough idle