Warm engine to normal operating temperature. Connect voltmeter to check connector. See CHECK CONNECTOR LOCATION table for location of connector.
Ensure positive probe is connected to "Ox" terminal and negative probe is connected to terminal "E". Start and race engine to 2500 RPM for about 90 seconds. Maintain engine speed at 2500 RPM and ensure voltmeter needle fluctuates 8 times or more in 10 seconds within 0-7 volts. If voltmeter fluctuates as indicated, oxygen sensor is okay.
If not, inspect hoses and wiring of fuel feedback control system and air suction system. See AIR SUCTION SYSTEM article. If no problem is found, replace oxygen sensor.

CHECK CONNECTOR LOCATION

Application

Location

Corolla FWD

Right Fender Apron Below EBCV

Corolla RWD Tercel Wagon

Right Fender Apron Below Wiper Motor

Pickup & 4Runner

⁽¹⁾ Near No. 2 Relay

Block Tercel Sedan

Near clutch reservoir tank

⁽¹⁾	See Fig 1.

Fig 1: Oxygen Sensor Testing (Pickup & 4Runner - Typical)

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Oxygen Sensor