Yesterday, my 2007 Nissan Versa’s Check Engine Light came on. I took it to a popular local hippie mechanic. They told me it was code P2A00:
A few things give me cause to be cautious about replacing this sensor:
-I got a similar error with my last car, I think, and a different mechanic told me it was nothing to worry about.
-When I asked the consequences of not fixing this problem, the mechanic sputtered something vague about damaging other components. She didn’t sound like she had a very clear idea of what the problem was.
-The same mechanic told me that I need battery service due to corrosion, but I got a new battery less than two months ago.
-The mechanic (or at least the front-desk person) didn’t know, until she was showing me my paperwork, that the light turned itself off during the final test.
-It’s the yellow “Service Engine Soon” light, not a red light.
-It’s $310 to replace it, and they don’t seem convinced that that’s even the problem. ($310 isn’t chump change for me)
I am also, of course, cautious about not replacing it, because:
-I don’t know much about cars, and I should probably trust the professionals.
-She may well have been telling the truth about its potential to damage other components.
I’ve Googled the code, but I’m having trouble finding out whether it’s a significant problem. So I turn to the teeming millions, possibly in the wrong forum, and ask: is this a serious problem, or nothing to worry about?
Obvious disclaimer: you are not my mechanic, you are not a mechanic practicing on my vehicle, consult a professional mechanic in all car-related questions.
From searching around the internet, this seems to be a semi-common problem on late model Nissans. Sounds like a bullshit emissions issue that won’t hurt anything (except maybe gas mileage). Most forums say to replace the O2 sensor, and one guy found that it was his gasoline cap.
I would find a mechanic that will let you bring your own parts so you can return them if it doesn’t fix the issue. Or you could drive with the check engine light on (if your state doesn’t require inspection as beowulff mentioned above) and take note of your gas mileage.
Advance Auto is my very dear friend as it has saved me thousands in the past ten years. No exaggeration.
I’m not sure–I’ll try that tomorrow. I suspect it does, however, given the fact that they told me there was some corrosion, and given the fact that it was off when I got the car back.
The code P2A00 means that the sensor is detecting that the engine is not running with an optimal air/fuel ratio. That does not mean that the engine is definitely running lean/rich just that the sensor is detecting that. It could be a cracked exhaust manifold but I would expect a P0420 (catalyst efficiency) code too and you would also hear an exhaust leak.
P2A00 could be a bad sensor but it could also mean something is causing your engine to run rich/lean.
Just a word of caution, when you disconnect the negative battery cable you are clearing all data from your PCM, including the idle control memory. Your engine may run rough for a while and may even stall until the computer learns how to idle your engine properly. I would recommend taking your car to Auto Zone or a similar parts store and they can check and clear your codes for you usually free of charge. This way you wont lose your idle memory and you will save your radio presets.
ETA:When you do reset the check engine light you will need to drive the car for a while before there is any chance the light will come back on IF it comes back on.
I forgot to mention in my last post is that if the sensor is telling the computer that the engine is running lean then it will try to add more fuel to the engine. If the engine was running fine but the sensor is insisting that it is lean then the engine will run very rich while the sensor is still saying lean. Excess fuel in your exhaust is poison to your catalytic converter and it may damage it.
Of course there are safety systems that help prevent this. Once a code is noticed by the computer it will usually run on an open loop system. This means that it will completely ignore what the Air/Fuel ratio sensor is saying and it will figure out how much fuel to give to the engine based on a pre-programmed chart. Basically it will rely on the other sensors of the engine to figure out what to do.
Seriously, always check for a loose gas cap, this *will *throw a code (i.e. lite the Check Engine light). Specifically the CE light only matters if your state has emissions inspections as well as safety (states with only safety inspections don’t care).
And unless you go to a friend or a true ‘backyard’ mechanic don’t try to bring your own parts to a real repair shop, they won’t want to install them and you shouldn’t ask them to. You don’t bring eggs to a diner and say, “Over-easy please”. And if your part looks like it was the least bit ‘installed’ (or if it’s electrical) a parts store will usually not accept a return from a retail customer. A reputable shop will do this for you, i.e. try replacing a sensor and if it doesn’t work return it themselves and not charge you for the part. Parts stores are more accepting of this policy with the repair shops they do regular business with.
I’ve worked on my own cars most of my life and replaced dozens of batteries (including in recent, highly computer-controlled cars) and I’ve never had this happen, not even once (other than losing the radio presets). The closest I had to this was when I had my sister’s tranny rebuilt. It was the first computer controlled transmission I’d encountered and yes, we had to do what you described (drive it around a bit till it ‘regained its mind’).
My VW polo started throwing up odd fuel/air warning lights. The mechanic told me to go away and fill her up with a tank of high octane fuel (100 UK octane. US octane uses a different scale) and run it through. Result: about halfway through the tank the warning light went out and never came back. He said it might have cleaned the crud off the sensors.
Now the sort of mechanic that gives you decent advice over the phone and talks himself out of an hours labour is worth keeping.
I am not saying it will happen every time but it does happen, especially if the vehicle has an Idle Air Control (IAC) valve and the valve is dirty. What happens is when you erase the memory the valve goes to a default position which may leave too small an opening for enough air to bypass the closed throttle plate. It takes a little while for the PCM to realize it needs to open the IAC valve a little more than default.
Perhaps since you work on your own cars and you more than likely maintain them very well you don’t have dirt build up on your IAC valve and you have never had this problem. Just a guess.
your mechanic sounds like a hack. there aren’t any “sensors” which the fuel comes into contact with that it could “clean.” I could almost buy that you might have had one or more fouled fuel injectors, but unless the higher octane fuel had a greater detergent content (not guaranteed, and octane number has nothing to do with that) then something else was going on. I’d wager it was something simple like a loose fuel cap triggering an evap emissions fault.