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Oxygen Sensors

I have a 2002 Toyota Rav 4 which I bought new. It has 43K miles and has been wll cared for. Two of the oxygen sensors have gone bad (I’m told there are 4?) and the cost to replace will be high. This is not a new occurance. They have been bad for several years (5?). Is it ok to dreive without them? I know it affects my gas milage, but can it cause any big-time damage? I’m on a fixed income and really can’t afford the replacement unless it is life threatening to my car. Thanks.

It’s unusual for O2 sensors to fail at such low mileage unless there is something causing them to fail.
It’s also possible to get O2 sensor codes which are caused by other faults and the O2s are fine.

Just a random thought, but your 2002 car only has a measly 43k miles from new and it’s difficult to fathom those sensors as having been bad for 5 years or being bad now. I wonder if the spark plugs are a bit iffy due to what is apparently short hop and scant driving use and that in turn is setting O2 codes.

I also realize that the recommendation on spark plug replacement is usually a lot longer than 43k miles but there are other factors that can make a shorter interval necessary.

My suggestion is to get a chain type parts house (AutoZone, O’Reillys, etc) to pull any codes for you and report back with any codes that may be present. This only takes a few minutes and they will do this for you free of charge. Hope that helps.

If the auto parts place says the oxygen sensor HEATER is bad (codes P0135, P0141, P0155 AND P0161), not the oxygen sensor, then driving the car for a while shouldn’t be a problem. If your state has an emissions test, you will fail it, so you must change them eventually

If the two failed sensors are on the same side, I’d suspect another problem, as @ok4450 suggests. I see from (internet auto parts house) that this car seems to have 4 sensors but only a 4 cylinder engine. That is unusual. Usually there would only be 2. All 4 look easy to access but cost about $110 each. Labor should not be very high for this, maybe another $100 to $150. Your 2 plus labor should be around $300 to $360. If their quote is way over that, look for another mechanic.

Dolly, is your Check Engine Light on?? If not, there may not be a problem at all…If the trouble code (if any) is for the REAR sensors, it’s safe to ignore those for a while…If you had your car diagnosed, the trouble codes found should be recorded on the invoice. Post those codes here and we can provide more detailed information…

How does your car start? Idle? Accelerate? Do you know what the gas mileage is? What kind of driving (short trips/long trips)?

Who says the oxygen sensors are bad?

How did they arrive at this conclusion?

I’ve heard of idiots condemning all the oxygen sensors when they had a P0171 and P0174 lean code

Good answers here but @db4690 is asking the questions that I would ask. I think that 50% of the oxygen sensors and catalytic converters replaced in this country for being faulty were really never faulty to begin with.

Goods points above, especially that the O2 sensors might actually still be ok. It would be very unusual to have two go bad at this low of mileage. The O2 sensor codes spit out by the engine computer simply mean the readings don’t correspond to what it expects to see. That can be – and usually is – caused by other problems than bad sensors, esp at this low of mileage. If an exhaust pipe or manifold is cracked, that is a frequent cause of O2 sensor codes. Mechanics have methods to test the O2 sensors to isolate the problem, and OP should ask if these tests have been done.

4 sensors in a four cylinder car? That would be more likely in a V6, where there are two exhaust banks, and two cats, so there would be two sensors per bank, one before the cat, and one after. In a 4 cylinder engine … hmmm … well I guess there could still be two cats, so one sensor before and after each cat.

The problem with just ignoring the problem is that the mixture may be way too rich or too lean, and that can damage other expensive-to-fix engine components, like the cats and/or the valves. And if you live in a state that requires inspections, the car may fail if the check engine light is on. In that case there is no workaround, you just have to fix whatever is causing the problem.

The check engine light has been on for several years, really! At first it came on and was related to the fact that my gas cap wasn’t properly tightened (per dealer). I corrected that and it was fine for a while and then came back on a few years later. I know it has been on at least three years, probably more. I was told it was the oxygen sensor where I get my oil changed and that it was ok to drive it, only the gas milage would be affected. I have had them check it maybe once a year to make sure nothing else is happening other than the sensor problem. The car starts, runs, accelerates as good as new. I haven’t had the spark plugs changed. No one has suggested that. I would like to avoid the dearler due to the fact that I know they would charge the highest possible. The labor at the oil change place was quoted at $32. per. The internet shows O2 sesnors as low as $30-$40. What sort of O2 sensors would these be? I just don’t want to be taken to the bank, but I really love this car and it’s great to drive and I want to keep it, but fix anything that requires it before I get into REALLY big money. Thanks to all.

The first step is getting the car scanned and posting back with any codes that may be present. There are a number of codes related to O2 sensors but that doesn’t necessarily mean one of the O2 sensors is actually bad.

I tend to agree with missleman about a large number of O2 sensors being incorrectly diagnosed and/or replaced.

The labor at the oil change place was quoted at $32. per.

There is a reason the repair rate may be low at the quick lube, quick tire, or quick muffler type places. They’re not known for their diagnostic quality.

Is that who told you your sensors were bad?

I had a 2002 Toytota Tacoma with an oxygen sensor that went bad at only 50k miles, so It’s quite possible your oxygen sensor has gone bad despite the low mileage. I put a new Bosch sensor in my Tacoma and the check engine light went away.

But first confirm the diagnosis by taking your car to an auto parts chain store and asking them to read the codes for free. Write them down in “P01234” format and post them here so we can tell what’s going wrong.

If you do replace the sensor(s) I would recommend using only the Denso or Bosch sensors. And don’t let your Quickie Lube place do the work. Find a recommended local mechanic in the Mechanics Files area of this site.

Most parts stores (like AutoZone or O’Reilleys) will read the stored codes for free…Have that done and post the codes back here.

Yes, the bad 02 sensors were diagnosed at a quick lube center. I need to ask around to find a garage that is reliable and check there. Thanks again to all who answered!

Look for a good shop by clicking “mechanics files” at the top of this page, or try yelp . com.

Not from personal expertise, but from listening to others, I would be much more likely to believe 50% of cat converters replaced weren’t bad.

Good comments about the brand of O2 sensors to use. I installed a $50 Denso O2 sensor in my Corolla recently it is working trouble free.

Re the cost of aftermarket O2 sensors. There’s at least two different kinds (technologies), and the cost is quite a bit different between the two. Some cars use both kinds, some cars (like my Corolla) use only one kind. O2 sensors are used by the computer to determine how much gasoline to inject to obtain the optimum fuel to air mixture. Too much fuel (rich) wastes gasoline and damages the cat; two little fuel (lean) can cause missing and overheating and could – over time – damage the exhaust valve. So it’s important that the mixture be correct.

The sensors that cost around $50 are the less-expensive of the two kinds, and sense either if the mixture is too rich, or if it is too lean. But not how much over-rich or how much over-lean it is. The other kind is more expensive, in the $150-$200 range (I think, I’ve never had to buy that kind myself), and they sense the amount of over-richness or over-leanness.

You don’t have a choice though which kind to buy. You have to buy the kind(s) the car originally came with. The only choice you have is the brand. I think Toyota uses Denso in its factory where they build the cars, so that’s a good brand choice for Toyota vehicles probably. But like mentioned above, before beginning a replacement regime, it’s a good idea for your wallet if nothing else to first determine the O2 sensor is actually bad.