I own a 01 Hyundai Sonata 2.4L and the error codes I get after an ODB check is p0171.

When i first start it up it's like it loses power, constantly hiccuping. So i have to press on the gas to keep it on. But eventually it goes back to normal when I drive across town it runs smoothly every now and then.

It says something about system 1 bank 2 lean or something. And it brings up a list of what the possible causes are, like a air leak, or fuel injector.

I wanted to know if anyone on here had the same problem as me, and would know what you really think it could be. Because from what the car does, it's like it loses power or pressure or something.

  • Are you sure it was sensor 1 bank 2?? Usually a number 2 in the second part (I say it that way because it usually comes out as bank 1 sensor 2) indicates the O2 which is after cat and has nothing to do with how the car runs. This is very pertinent in diagnosing what is going on with your car. Commented Jul 23, 2014 at 21:15

1 Answer 1


Code P0171 is a pretty general code for 'engine running weak'. Running weak means too much air, or, not enough fuel. The main culprits are a loose or damaged vacuum hose, EGR valve staying open, EVAP system leaking air into the system, faulty fuel injector(s), or a leaking exhaust system. It does not seem to be the oxygen sensor to me because you have rough running from start-up. The oxygen sensor comes into play once the vehicle starts to warm up. To isolate the problem will need a scan and possibly a couple of systems tests to pinpoint the fault.

  • when I run a scan, everything is in RDY mode except, CAT, EVAP & O2S. I have a feeling it's an o2s because i've driven this car for countless miles and it still will not show up as ready for the o2s. Commented Aug 4, 2014 at 22:14
  • All of the componenets on your engine management have 'monitors' - check routines that run when the engine runs and set the systems to ready. The Cat, EVAP, O2S all work with each others readings to set ready on each other. You need to do a leakage test on the EVAP to prove its sealing properly. If its not sealing the system cannot check the O2S. If the O2S is not working the system can't check the Cat or the EVAP. You can check the O2S by a propane test, or bite the bullet and fit O2S. May I recommend a little reading, The Auto Emissions Bible-Sam Bell/Ralph Brinbaum, $21? Commented Aug 5, 2014 at 9:45

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