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My 2012 Volvo C30 T5 has been having a recurring engine code P2196 (O2 Sensor Stuck/Biased Rich) for some time now. It has popped up on four or five separate occasions. I usually clear it, but one time it went away by itself during a 2-hour drive at highway speeds.

At first, I noticed that it seemed to pop up when going through a touchless car wash, specifically at the very moment that the underbody was sprayed with water. This happened twice. I thought maybe a boot was torn and the water was causing a sensor to report a value out of spec. But, it also popped up a couple of times while idling or driving slowly, which is what I do when I’m going through the car wash, so it could just be linked to idling/driving slowly.

Context, I typically do lots of city driving and little highway. The user manual recommends premium, but states that regular fuel will not damage the engine. I had been putting in premium, even 94 at one point, to try to clear the issue, but to no avail. One day, I filled up with regular 87 in preparation for a 2 hour trip at highway speeds. To my surprise, the light went away during this drive. Not sure why.

Anyway, all this seems to point to a bad O2 sensor. But, when I did an “O2 Sensor Test” with my OBDII code reader, the test passed.

What could this mean? Should I try replacing the upstream O2 sensor anyway?

More context: ODO is at 150,000km (93,000 mi). Oil is always changed on time, with synthetic . Air filter looked fine last I checked, and I think the spark plugs were changed recently, but not sure about the fuel filter or PCV system. I do lots of 10 minute trips from a cold start, we do have long cold winters here, and the car is garaged most of the time.

ivorysoap
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The O2 sensor is covered in soot and other deposits. The improvement with highway driving and use of regular/87 octane is a dead giveaway. The lack of highway driving exacerbates the problem. Replacing the sensor(s) will eliminate the problem only for a time, then return before long (unless, perhaps, the sensor has 150k+ miles).

What is the car's mileage? Deposit buildup gets worse with age, but happens routinely even on a brand new car with very low mileage. How is the condition of air filters & fuel filters, spark plugs & wires, PCV & EGR valves (if applicable), vacuum hoses and other tune-up parts? Has the motor oil been changed regularly? You've already mentioned city driving. How about short trips under 15 minutes from cold startup? Do you live in a climate with long winters? Is the car garaged? All of these factors accelerate deposit buildup.

There are a number of additives you can use to clean up an engine, which I I've used with great success if you're interested. It is, however, most cost effective to start with the basics and provide this forum with more complete information.

Carguy
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