Today: The case of the buzzing oil light.

Dear Car Talk

Dear Car Talk | Jan 01, 1995

Dear Tom and Ray:

I own this beautiful, cream-colored, 1985 Audi 4000 with 42,000 miles and I love it. I use it mostly for shopping, and it hasn't failed me yet. It does one annoying thing, though, that infuriates me. For no reason that I can find, the red oil warning light comes on and the buzzer sounds. This car has an oil gauge, which does not show any drop in pressure, and when I take my foot off the accelerator, the light goes out and the buzzer stops. My mechanic has checked and says not to worry about it. He tells me to keep my eye on the gauge and forget about the light and buzzer. What do you think?

RAY: What your mechanic doesn't realize, Josephine, is that this car has two oil sensors. One turns on the warning light and buzzer when the oil pressure is too low, and a second one sounds the alarm when the oil pressure is too high. My guess is that your high pressure sensor is the one that's going off.

TOM: He's probably put his own gauge on your engine, and determined that you don't have LOW oil pressure. That's why he feels confident telling you to forget about it. What he has to do now is use his gauge to determine whether you have HIGH oil pressure.

RAY: I've managed to convince my brother that this test can only be done while the car is moving. So I always strap him to the top of the engine, close the hood as best I can, and have him take a reading while I drive around at high speed.

TOM: But in reality, all your mechanic has to do is hook up his gauge, and rev the engine while he takes a reading, because the oil pressure is directly related to the speed of the engine, not the speed of the car.

RAY: If he does find a high pressure problem, a new pressure relief valve will probably solve it. If the pressure is fine (and you're still getting the light and buzzer), the problem could just be a faulty sensor. Good luck, Josephine.

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