Virtually every Toyota made since the 1980s has sensors that measure the amount of oxygen in the exhaust, then transmit that signal back to the ECM so it can determine the proper air/fuel mixture for the engine — helping your car to run as efficiently as possible while reducing emissions. That’s the basic function of the O2 sensor, here’s what you need to know about oxygen sensors and their failure.

How Does An Oxygen Sensor Work?

Your Toyota’s oxygen sensor works as a monitor — the tip is placed inside the exhaust pipe and detects the amount of oxygen in the exhaust. If there is too much oxygen, it’s too lean, and too little would be too rich, it sends a signal to the ECM to adjust the mixture. When your O2 sensor is going bad, your ECM can’t probably adjust the mixture.

Signs Of A Bad O2 Sensor

When an oxygen sensor is bad in your Toyota, expect the following issues:

Poor fuel economy. Depending on the location of the sensor, the fuel delivery, and combustion systems can become extremely irregular by a bad O2 sensor. If too much fuel is sent to the engine, it will cause gas mileage to suffer.

Engine pinging. A bad O2 sensor can cause timing issues that will cause engine pinging. This occurs when the combustion gases ignite at the wrong time.

Rough engine idle. When your Toyota has a bad O2 sensor, it will often idle irregularly or roughly.

Engine misfires. A bad oxygen sensor can disrupt the engine's combustion, causing it to misfire. These misfires are usually more pronounced at lower idle speeds.

Engine trouble codes. This is the easiest way of knowing if your Toyota has a bad oxygen sensor — it will send a DTC to the ECM. Usually, the check engine light will illuminate on the dash, but this sometimes doesn’t happen right away, so scan it for codes. (Check out the details we've shared on engine codes in this post and this one, too.

Replacement

Once you determine the oxygen code is in need of replacement, you need to address this part right away. Replacement with a genuine Toyota oxygen sensor is simple and can be done fairly quickly. Here’s how it’s done:

• Find the oxygen sensor by looking for a spark plug-looking part connected to your Toyota’s exhaust — it will have an electrical connection on it.
• Disconnect the electrical connection using a flathead screwdriver to push in the tab and pull the connector apart.
• Unscrew the O2 sensor from the exhaust pipe using an open-ended wrench.
• Reverse the steps to replace the new sensor, making sure not to overtighten to the sensor so you won’t strip the threads.
• Plug the connector back in.
• Use a scanner to clear the code by turning your car to the run position without cranking it, clear to code with the scanner.
• Crank the car, you should notice a fairly significant difference at this point.

Remember to only use OEM quality oxygen sensors and related replacement parts to avoid damage and premature failure to the affected systems.