exhaust

O2 Sensor - Upstream

for 2018 Ford F-150 3.5L V6 EcoBoost · RWD

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

Difficulty

Easy

Time

36 min

Tools

Steps

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

This procedure covers the replacement of the upstream (pre-catalytic converter) oxygen sensor on the 2015-2020 Ford F-150 with the 3.5L EcoBoost V6 engine.

Warnings

⚠️Exhaust system components can remain extremely hot for over an hour after engine shutdown. Allow adequate cooling time to prevent severe burns.

⚠The oxygen sensor is fragile and contains ceramic elements. Do not drop or strike the sensor as this will damage it.

⚠Never apply anti-seize to the sensor element or connector. Apply only to threads.

ℹ️The 3.5L EcoBoost has two banks with upstream sensors on each. Bank 1 is the passenger side, Bank 2 is the driver side. Verify which sensor triggered the fault code before beginning.

Tools required

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

3/8" drive ratchet with extensionEssential

Wire brush

Anti-seize compoundEssential

Penetrating oil

Jack and jack standsEssential

Wheel chocksEssential

OBD-II scanner

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

Parts

Upstream oxygen sensor (Bank 1 or Bank 2) × 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

Park vehicle on level surface and engage parking brake. Chock rear wheels.
Allow exhaust system to cool completely if engine has been running (minimum 2 hours recommended).
If necessary for access, raise and support the front of the vehicle on jack stands at the frame rails.
Use an OBD-II scanner to identify which oxygen sensor has failed (Bank 1 or Bank 2, upstream or downstream).
Locate the upstream oxygen sensor on the appropriate exhaust manifold before the catalytic converter. It will have a wiring harness connector.

Procedure

1
Disconnect electrical connector
Locate the oxygen sensor electrical connector. Press the release tab and carefully disconnect the wiring harness from the sensor. The connector may be secured with a clip or bracket on the heat shield - remove if present.
2
Apply penetrating oil
If the sensor has been installed for an extended period, spray penetrating oil around the sensor threads where it enters the exhaust manifold. Allow to soak for 10-15 minutes. This will help prevent thread damage during removal.
3
Remove old oxygen sensor
Using the O2 sensor socket and ratchet with extension, carefully loosen the oxygen sensor by turning counterclockwise. The sensor may require significant force to break free initially. Once loose, unthread the sensor completely by hand and remove it from the exhaust manifold.
4
Clean sensor bung threads
Use a wire brush to clean the threads in the exhaust manifold sensor bung. Remove any carbon buildup, corrosion, or remnants of old anti-seize compound. Ensure threads are clean and undamaged.
5
Prepare new oxygen sensor
Remove the new oxygen sensor from its packaging. Apply a thin, even coat of anti-seize compound to the threads of the new sensor only. Do not allow anti-seize to contact the sensor tip or electrical connector. Verify the sensor is the correct part for your application.
6
Install new oxygen sensor
Thread the new oxygen sensor into the exhaust manifold bung by hand to ensure proper thread engagement. Once hand-tight, use the O2 sensor socket and torque wrench to tighten to specification. Do not over-tighten as this can damage the sensor or exhaust manifold threads.
Torque spec
O2 Sensor45 Nm (33 lb-ft)
7
Reconnect electrical connector
Route the sensor wiring harness to avoid contact with hot exhaust components or moving parts. Connect the electrical connector to the sensor until it clicks into place. If applicable, secure any wiring clips or brackets to the heat shield.
8
Lower vehicle and clear codes
If the vehicle was raised, carefully lower it from the jack stands. Use an OBD-II scanner to clear any stored fault codes related to the oxygen sensor. This will reset the check engine light and allow verification of the repair.

Reassembly

Ensure all wiring connectors are fully seated and secure.
Verify the sensor wiring is routed away from exhaust heat and moving components.
Double-check that any heat shield brackets or clips removed during the procedure are reinstalled.

Verification

Start the engine and allow it to reach normal operating temperature while monitoring for unusual exhaust leaks near the sensor.
Check that the check engine light does not immediately illuminate after starting.
Use an OBD-II scanner to verify the new oxygen sensor is providing data and no fault codes are present.
Perform a test drive of at least 10-15 minutes, allowing the engine to cycle through various loads and speeds to ensure the sensor is functioning properly.
After the test drive, re-scan for codes to confirm the repair was successful and no new faults have been triggered.