Necessary to clean O2 sensor?

I’ve got a 2000 VW Lupo 1.4 automatic. (It’s a smaller hatchback version of the Golf). Acceleration is a bit sluggish and the gas mileage is a bit lower than it should be, compared with other Lupos. Combined mileage is about 31miles/US gallon. I’ve been doing the usual things to improve gas milease; new ignition leads, plugs, cleaned the throttle body and the MAS sensor, to some good effect. The question now is should I clean the downstream O2 sensor? As the sensor is screwed into a rusted exhaust manifold, I’m concerned that trying to unscrew it, even with the aid of some de-rust spray, might turn a small problem into a big problem if the thing breaks off.

So far car’s computer has no warning about the O2 sensor. Has anyone had good experience with gas additives like Wynn’s that promise to clean the O2 sensor? Any advise, suggestions welcome.

Thank you.

My advice is, unless you have real proof the O2 sensor is the problem, don’t ask for trouble. Leave it alone.


It’s the upstream sensor that affects mileage, driveability, and emissions. The downstream sensor only exists to validate proper catalytic converter operation.


Thank you for this. Is the upstream O2 sensor the one attached to the exhaust manifold?

Yes, the upstream sensor is the one on the exhaust manifold.


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Just curious.
How many miles has that upstream sensor been in there?

Is there a reason you’re trying to clean it rather than just replacing it?

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If I can believe the odometer the car’s got about 50,000miles on it. I’m inclined to clean rather than replace the O2 sensor only because cleaning is cheaper, easy to do and, from the advice I’ve gotten, works perfectly well to restore the sensor, assuming you’re starting out with one without defects.

You’re assuming the O2 sensor is the reason for your problems. I doubt seriously that it is. I wouldn’t touch it without first running a curve on its output signal. If it were out of spec it’d be tripping a fault code.

I’d’ start by assessing the engine’s overall condition with a compression test. Since cleaning the throttle body seems to have helped, that would suggest to me that you had some carbon buildup. That would in turn suggest that perhaps the engine is tired. By “tired” I mean cylinder wear and loss of tension on the piston rings, compression and/or oil wipers.

Check the compression and post back.

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Agree with the others. But if you do remove it, replace it with an identical new unit. I wouldn’t try cleaning it, I doubt that would do any good, could do harm.


I agree.

  • the requisite %&$#@ ten characters.
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Thank you. I’ll ask my mechanic to check the compression.

Super. Be sure he gives you the actual numbers.
But, since you’re taking it to a mechanic, allow me to suggest that you tell him your concerns and let him diagnose it. And, if the cost is reasonable, to fix it. Then, if you like, you can tell us everything. We do care.

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Cleaning an O2 sensor is a useless venture. It can’t help.

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Check the manufacturers instrutions for cleaning the O2 sensor, it is located in the same file as cleaning catalytic converters. Can’t find the file? That is because you do not clean these devices. Once they have served their useful life they are replaced. The only thing you might have an outside chance of cleaning is carbon gunk build up on the sensor. But if you have this type of build up you have bigger problems that need to be addressed first. The snake oil sold to clean the sensor is great for the bottom line of the supplier but has little or no value to the user.

Besides compression inspect spark plugs, check that the thermostat is allowing the engine to warm up to proper temperature, check fuel pressure, check for dragging brakes (hot wheel).

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The symptoms described don’t sound like an O2 sensor problem. I’ve never heard of anyone cleaning one, but I suppose a person could try it. If the cleaning treatment ruins it and it starts throwing a code, inexpensive to replace with a new one. I don’t see much down side to it. But I don’t see much upside potential either. For reduced mpg the OP would be more efficient spending diy’er time to make sure the coolant temp is getting to the manufacturer’s specifications for a warm engine. Thermostats eventually warp and don’t close all the way, which can reduce the coolant temp slightly. And even a slight drop in coolant temp will reduce mpg.

If OP decides to clean the O2 sensor anyway, probably both the outside (the part outside the exhaust stream) and inside should be cleaned. O2 sensors have a passageway to allow outside air into the sensor part inside, and that can get clogged up and prevent accurate O2 readings.