Will a bad O2 sensor reduce my fuel economy by 20 percent? More than a catalytic converter?
Possibly. But o2 sensors are pretty robust, not a common failure item. Is there a reason you think the o2 sensor is faulty, beyond the reduced fuel economy? Among simple reasons for reduce fuel economy is a faulty engine coolant temperature sensor. Computer injects more gas b/c it thinks the coolant is cold, when it isn’t.
What is the actually code number you are getting?
No, that is wrong. Very common failure item in a 12 year old car.
And Yes, a bad O2 sensor will cause your car to use more fuel if it is the one nearest the engine.
Why are you asking? We need more details here.
Don’t know the number that is registering on the diagnostics, but the mechanic says it’s a catalytic converter. Which apparently sometimes means the O2 sensor.
Was it P0420?
If so, every vehicle that came into my shop with this code had to have the catalytic converter replaced.
Interesting. I don’t see that by the posts we get here. Lots of theories about poster’s thinking their pre-cat o2 sensor is bad and causing lower mpg of course, but not much presented in the way of evidence. O2 sensor failures by what I see here are mostly wiring or heater circuit problems, not the sensor itself. Those usually cause o2 sensor diagnostic codes specific to an o2 sensor, which OP doesn’t mention.
My 30 year old Corolla is on its second o2 sensor, but I doubt there was actually anything wrong with the first one. After removed, it tested ok in the propane test.
I have personally changed 3 of 4 on my 150k truck. One of 4 on my 85k Mustang and none on the Audi.
I think you may be right that since the O2 sensor has its own codes, diagnosis is easy as is the fix so they don’t come here and ask for advice.
I’m going to be very blunt
If your mechanic said “it’s a catalytic converter” you most likely have a P0420 or P0430 catalytic converter low efficiency fault code, which is usually due to the catalytic converter itself, not the oxygen sensor(s)
How critical is it to replace the catalytic converter, if you’re in a state that does not check emissions? And also would the catalytic converter cause your fuel efficiency to drop by 20%?
Well, we all breathe the same air, don’t we? For other reasons, see answer below.
Yes, if the cat was clogged it could easily drop your fuel efficiency by 20%. And more as you continue driving it.
If you don’t get the Check Engine light to turn off, it’ll be on all the time.
Then, if something else goes wrong that would normally turn on the Check Engine light, you’re not going to know it.
And that something else could leave you stranded or damage the engine.
Does your state have emissions inspections?
If so, does your car have CA emissions?
No emissions standards. When I fill up my fuel tank, the check engine light goes off and my mileage goes up to 26 miles per gallon. Before long the check engine light comes on and my mileage drops, at the current rate, to 19 miles per gallon. Is it safe to assume that the oxygen sensor would create that kind of a fuel problem?
No, O2 sensor failure doesn’t seem a likely explanation for the symptoms imo. I guess you could try replacing the car’s O2 sensors and see what happens. Keep possession of the old ones b/c they came with the car as oem parts, they’ll likely better quality than the replacements. Note that your car probably has at least two O2 sensors, possibly more. This complicates the replace and hope for the best idea. IMO your best bet is to obtain a proper shop diagnostic, then if the diagnostic says something needs replacing, replace only that part.
I’m guessing you have either a cat problem or an exhaust leak.
Come on now George, we all know it’s more fun to keep guessing and spending more money on things that don’t fix the problem, and then come back here and complain about how much was spent not fixing it.
Professional diagnosis, now that’s no fun at all.
The most fun would be to buy/rent the shop tools needed to make the diagnosis and make it a diy’er project. If this car had OBD I tech replacing a sole O2 sensor on a flier might make sense, but on a 2010 w/ OBD II … not so much …
By then you may have spent more than the diagnostic fee would have been.
Proof that more fun costs more money.