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Change O2 Sensor @ timing belt change?

1999 Integra Auto 80k
Firstly I don’t even know what is O2 Sensor.

When doing Timing Belt, Water Pump, valve adj, should I also change the O2 sensor? Not sure how much are these yet. Are there other sensors?


I wouldn’t change it unless there’s a problem. Your check-engine light isn’t on at the moment, right?

Most sensors aren’t replaced proactively, but when they have problems. However, if there’s an overlap in the jobs, that would make an important difference. If the sensor is under the timing belt cover, then I’d probably replace it. I believe that would be an unusual configuration. Every vehicle I’ve ever seen had oxygen sensors out in the open.

While most sensors aren’t replaced proactively, some people recommend replacing oxygen sensors (at least the pre-cat sensors) every 100,000 miles. I don’t have the expertise or experience to agree or disagree with that, but replacing it couldn’t hurt, and could possibly prevent problems with the catalytic converter. I replaced mine proactively at 11 years, but it also had 230,000 miles on. I probably wouldn’t replace it in your case. If you decide to do it later, it’s completely separate from the timing belt, so you don’t duplicate labor costs.

That said, I hope this isn’t the first time you’re replacing that timing belt. There should be replacement intervals in both years and miles. In spite of the low mileage, I suspect you’re approaching the interval for the second change based on years. Those belts can break due to age, even if the car hasn’t been used much.

You don’t need to replace the O2 sensor. If the crosscounts of the O2 sensor slow down or if there’s a problem with the heater circuit of the O2 sensor the Check Engine light would be on. Why spend about a $100.00 for something the vehicle doesn’t need?


Of the last 5 vehicles we’ve owned with a total mileage over 1,000,000…I’ve replaced ONE O2 sensor.

A new O2 sensor improves gas mileage. My estimate is about 2 mpg or more.
If one drives 15,000 mi/yr at 30 mpg then total gals = 500 gal.
If replacing the O2 sensor boosts mpg to 32 mpg, then
if one drives 15,000 mi/yr at 32 mpg then total gals = 469 gal.
Total gals saved in one year is 31 gal.
With gas at $3.50 / gal, total yearly saving = $109.
A new O2 sensor costs about $100.
So payback time for replacing an old O2 sensor (but one not throwing a code) is about a year.
DIY O2 sensor replacement takes about 1/2 hour. (Book rate is 0.7 hour.)
Only equipment required is a special socket.
Seems like replacing an aging O2 sensor is not a bad idea.

Wait till the Check engine light turns on.

Many times the O2 sensor fails due to another part the engine not working correctly. Yes they do occasionally fail however it does not do much except light up that yellow nag light.

I did my first o2 sensor on vehicle recently on my Subaru WRX at 7yrs/83k miles I recently sold.

A new O2 sensor improves gas mileage.

Hows that?? If an O2 sensor is NOT working properly it’ll cause a code in the ECU. If it’s working properly I don’t see how replacing a working O2 sensor is going to save money.

sciconf, there are usually two O2 sensors under the hood (on a basic four cylinder engine), and they basically measure the amount of Oxygen in the exhaust, one before the exhaust gasses pass through the catalytic converter, and one after the exhaust gasses pass through the catalytic converter. They basically measure how much fuel gets burned and how well the catalytic converter does its job.

If your “check engine” light is on, and the code is related to one or both of the O2 sensors, it could mean that one or both of the sensors are bad, that the catalytic converter is no longer doing its job as well as it is supposed to, or that there is a problem with the air/fuel mixture. In any case, O2 sensors are usually too expensive to be replaced prophylactically. Wait until your car has a malfunction before you replace one or both of them.

MikeInNH makes a good point. A PROPERLY WORKING O2 sensor (vs. a malfunctioning O2 sensor) will improve fuel economy. However, there is no reason to replace a good O2 sensor with a new one. In addition, you would need to do precise testing in a laboratory environment to know with certainty that your fuel economy improved by a margin as small as 2 MPG. 2 MPG is well within the margin of error of most techniques used by laymen to measure fuel economy.

In real everyday life, there are so many other factors that could lead to a 2 MPG improvement that there is no way to know it was the O2 sensor that made a difference. Mechaniker might have replaced his O2 sensor during the spring, as temperatures were rising, or maybe the guy who sold him the O2 sensor over-inflated his tires to make him think the O2 sensor made the difference, or maybe the planets happened to be aligned that day, and he drove in a tailwind the day he measured his fuel economy. There’s no way to know for sure how, or even if, he got better fuel economy and why, unless he tested the car in a lab both before and after the installation of the new O2 sensors.

I never change an 02 sensor until the check engine light comes on. If your 02 sensor is bad it will likely cause a significant drop in fuel efficiency. I have had them go bad and cause as much as 20-30% decrease in gas mileage.