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I'm leaving on a 800 mile trip tomorrow and check engine light came on. Took it to autozone and computer said it was the o2 sensor. Is this something that should be replaced prior to the trip or can it wait?

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    It will adversely affect your fuel economy. But than again autozone sells parts and does not diagnose cars so something worse could be wrong with it. – vini_i Jan 2 '17 at 0:26
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    Which O2 sensor did it say was a problem? Upstream or downstream? – Pᴀᴜʟsᴛᴇʀ2 Jan 2 '17 at 0:36
  • What was the exact code that was set? You should investigate the particular code for your vehicle before you replace any parts. – Robert Stiffler Jan 30 '17 at 6:14
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Given that typically cars these days have two O2 sensors, there is some level of redundancy. Also, do note that the car when warming up operates in an open loop mode. The absolutely worst that could happen is that your car continues to operate in an open loop mode even when warmed up. It may mean worse fuel economy and possibly higher emissions.

So, if you ask from Greenpeace, they will probably say that the car should not be driven. But my opinion is that you can perfectly well take the trip and replace the sensor when you have time for that.

  • There's not any redundancy between the two oxygen sensors because the upstream and downstream sensors measure different things. The upstream sensor measures the oxygen concentration before the catalytic convertor and provides feedback to the ecu to help adjust the air fuel ratio. The downstream oxygen sensor measures after the catalytic convertor and ensures that catalyst is working properly. They are not redundant at all. – Robert Stiffler Jan 30 '17 at 6:17
  • -1 because like Robert said o2 sensors do not have redundancy and secondly because a bad o2 sensor may cause serious power delivery issues or at least awful gas mileage. – Gabe Wisneski May 25 at 18:22
  • On most control systems designs where pre and post catalyst sensors are used the system can and does, to some degree, use both sensors for fuel control. Both report mixture to the PCM, so it can use both for fuel control if the engineers chose to do so. The only vehicles that I have found that do not use the post cat sensor for some degree of fuel control are late 90's Subaru. – Fred Wilson Jul 16 at 6:24
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You can do either, if you drive in town short distance then leave it, and maybe the long drive will clean it and it will be fine after. It won't cause any problems on the trip except maybe? Your mileage won't be optimum.

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The O2 sensors do a couple of things each. The one above the exhaust is there to tell the CPU, that the air/fuel mixture is perfect and can only work with the ambian temp from the sensor in the water jacket and the Mass air flow sensor in the intake. The MAF tells the CPU how much air is coming thru, the ambiant temp sensor tells the CPU that the engine is warm enough to run in normal mode the crank sensor tells the CPU when to inject fuel for a maximum imput and the camshaft sensor tells the CPU when to set off the spark. Now the O2 sensors tell the CPU that the mixture is perfect and the one after the exhaust checks the amount of co2 and when the ambiant temp sensor tells the CPU it's warm enough then the O2 sensor tells the CPU to open the valve between the positive Crankcase Ventilator and the intake manifold to burn the excess gas. Until it's warm enough then the excess gas goes into a carbon filled tank which holds the gas until it's warm then the O2 sensor tells the CPU to open it up and the car... Runs great . I would not like to have my engine turned into a stationary engine, and that is basically what happens when the CPU doesn't get the signals it needs. It keeps putting the engine into start up mode. Then you get to take it to a dealership to get the CPU reset. $1,700.00 is about what it was when I worked for one. I was just a tow truck driver.

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