An oxygen Sensor question, from our Three Stooges department.

Dear Car Talk

Dear Car Talk | Apr 01, 1991

Dear Tom and Ray:

I'm standing at one of these "while-u-wait" tune up joints, having just agreed to pay 80 dollars for something called an oxygen sensor for my '83 Buick Skylark. The guy with the clipboard pulled me over, pointed to an innocuous little knob on the back side of the engine, and said it's part of the computer and needs to be replaced. I said OK, and am now waiting for my car and feeling like a stooge. I'm used to being stooged for 5 dollar filters, but being stooged for an 80 dollars computer mystery part is new to me. What would happen if I didn't replace it? How could I know if it needs replacement? Am I a stooge?

TOM: You may be, John. The oxygen sensor is not part of the computer as you say in your letter. It's actually a device that sends information TO the computer. It tells the computer how much oxygen is in the car's exhaust, and the computer uses that information to determine how much fuel to mix with the incoming air.

TOM: If the oxygen sensor isn't working, one of two things can happen. Either the computer will add too little fuel, and the car will run roughly. Or, even worse, the computer will add too much gas, and your catalytic converter will get ruined.

RAY: To prevent that kind of damage, the designers of this particular car arranged for the "Check Engine" light to come on whenever the oxygen sensor malfunctions. Since you don't say anything about the Check Engine light in your letter, we're left to wonder how the mechanic knew the sensor needed changing.

TOM: So our conclusion is that either the Check Engine light was on, and you aren't telling us the whole story, John. Or "John" is an assumed name, and your real name is Larry, Curly, or Moe.

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