Must I replace my oxygen sensor?

Dear Car Talk

Dear Car Talk | Apr 01, 1990

Dear Tom and Ray:

I drive a late model car. At 30,000 miles, the oxygen sensor light came on. I have gotten conflicting opinions about the importance of replacing the oxygen sensor when this dashboard light comes on. One mechanic told me it's necessary for the car to run properly and efficiently. Another said that it was only for emission control requirements and wasn't needed for the car to run properly. Do I need to spend the $300 (estimate) to replace it?

RAY: That's a very good question, Larry. The oxygen sensor IS necessary for the efficient and clean operation of the car, but you DON'T necessarily have to replace it just because the light comes on.

TOM: What the oxygen sensor does is constantly measure the amount of oxygen in the exhaust. It then sends those readings to the car's computer, which continually adjusts the fuel/air mixture. If the sensor isn't working, the car will run poorly and will pollute the air.

RAY: The "oxygen sensor" or "emissions" light on your dashboard comes on for one of two reasons. Either there IS something wrong with the oxygen sensor, or it's simply time for the emissions system to be serviced.

RAY: Most cars call for emissions service at 30,000, so I'm going to guess your light was tripped by the odometer, rather than a malfunction. But regardless of why the light came on, you should take the car to a mechanic.

TOM: If everything is fine, your mechanic can simply reset the dash light (which will then come on again at 60,000). Don't bother trying to reset it yourself. The manufacturers have learned to hide the reset buttons so people like you won't be tempted to skip the emissions service.

RAY: If it turns out something is wrong with the oxygen sensor, or if the manufacturer calls for a replacement at 30,000, then you'll have to replace it. Since you didn't tell us what kind of car this is, check your owners manual to see if a new one is required.

TOM: One final thought, Larry. $300 is an awful lot to spend on an oxygen sensor. Unless you're driving something like a Mercedes, an Audi, or the Starship Enterprise, you should spend $150 or less.

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