How accurate are the Autozone computers that check warning lights?

[SAWYER]

I took my wife's vehicle(Chrysler Pacifica) to have it check and was told it's an oxygen sensor. I wouldn't doubt it as the mpg has been horrible. I replaced an oxygen sensor on an old vehicle I had and it just screwed in, I would guess this is similar. Can an oxygen sensor really cause that much of a decrease in mpg?

 

[LTC8K6]

OBD2 is OBD2 but the codes can sometimes mislead you.

 

[jlee]

Yep.

There's not really anything to dispute about the accuracy of the reader itself..all it does is pull whatever code(s) the engine's ECU is throwing. What exactly that code means may be a little tougher to figure out.

 

[StageLeft]

Concur both last posts.

I have heard O2 sensors murdering gas mileage but I think it's an exception rather than the rule, but if you have that code you may as well do it.

 

[PottedMeat]

Can you clear the code and see if the same one comes up again?

 

[CrackRabbit]

O2 sensor codes are often signs of trouble farther up the line.
Likely a vacuum leak at or just past the throttle body.

I had the same issue with my Focus, turned out the vacuum line going from the PCV valve to the throttle body had rotted out causing the mixture to lean out, the computer was compensating by dumping fuel to try and bring it back in to spec causing horrid gas mileage.

Check all of the rubber hoses going to the intake manifold and throttle body, I bet you have a crack or hole in one or more of them.

 

[amdhunter]

I had a couple of o2 failures on my cars over the years. Changing the sensor worked perfectly each time.

I remember modding an o2 sensor on my old Galant to get it to work...lol. I'd never attempt that today.

 

[StageLeft]

I had a couple of o2 failures on my cars over the years. Changing the sensor worked perfectly each time.

I remember modding an o2 sensor on my old Galant to get it to work...lol. I'd never attempt that today.

I've had two go bad and replacing each worked just fine, no recurring codes (before that I had reset several times and the same code would always come back).

 

[kornphlake]

O2 sensors do go bad, usually around 100k since that's about when the emissions warranty expires. As mentioned there are other problems that will trigger the same code depending on what code it is. Did the auto parts store write down the code for you? Often googling the year and model with the trouble code will turn up some pretty helpful results. When a mechanic wants $100 just to diagnose the problem, a lot of people turn to the internet for free answers. Unless you're incredibly unlucky you're not the first person to have this problem.

 

[hanoverphist]

Yep.

There's not really anything to dispute about the accuracy of the reader itself..all it does is pull whatever code(s) the engine's ECU is throwing. What exactly that code means may be a little tougher to figure out.

ed zachary.

i just replaced my o2 sensor, and yes it will tank your mpg if its the upstream o2 sensor. mine went from 16ish to 7.5mpg while that sucker was bad. the code i was given had a few different meanings, had to run down the list of 6 things before i got to the o2 sensor, and it was confirmed with a mechanic that had experience with the symptoms.

check the code online with your car year and make, read up on them before doing anything expensive.


edit:

O2 sensor codes are often signs of trouble farther up the line.
Likely a vacuum leak at or just past the throttle body.

I had the same issue with my Focus, turned out the vacuum line going from the PCV valve to the throttle body had rotted out causing the mixture to lean out, the computer was compensating by dumping fuel to try and bring it back in to spec causing horrid gas mileage.

Check all of the rubber hoses going to the intake manifold and throttle body, I bet you have a crack or hole in one or more of them.

also the same thing that happened to me. the pcv valve hose was solid as a rock, and was seeping.