i got a quick question. I own a 2001 Hyundai Sonata 4cyl with 180,000 miles.

I have 3 monitors in not ready mode:

  • EVAP
  • O2S
  • CAT

I got a check engine line code for p0171, bank 1 system too lean. I think i've fixed the issue, which could've been a dirty MAF, as i couldn't spot any leaks in the air intake.

What I'm asking is, how do I get these monitors in ready mode? Was it because the system was "Too Lean" that CAT & O2s failed to function? I don't think it's a bad sensor, as it'd throw the CEL on with a sensor that may be bad. Same with the CAT or EVAP.

So should i do drive cycles after i fixed the p0171 code to see if the monitors will go back in ready mode?


  • This is the same basic question as what you asked previously. Asking the same question over again is not going to get you different results. Aug 9, 2014 at 0:37
  • The underlying question in the first episode was really specific to the O2 sensor. I think this question is about how to clear the "not ready" after hypothetically fixing the problem - drive cycles, scantool clear, etc. Aug 9, 2014 at 2:56
  • TrippedStackers, I'd run the drive cycles. Chances are pretty good that the computer will figure out that everything's working right again... provided, of course, that it IS. Aug 9, 2014 at 2:58
  • My point is, asking different questions on the same problem will not yield you different results. You should have either modified your previous question with an edit or put a bounty on it to get more attention. Aug 9, 2014 at 14:22

1 Answer 1


The following is a summary of generic OBD II drive cycle instructions for a Hyundai:

  • The Intake Air Temperature (IAT) should be between 14 and 122 degrees F.
  • Barometric pressure should be equal to or greater than 75 kPa.
  • The fuel tank should be between 25 and 75% full at the start of the test.
  • During acceleration, keep throttle 1⁄4 to 1⁄2 open.
  • During deceleration, slow to less than 15 mph at an engine speed of less than 1000 rpm without touching the brake or clutch pedal.
  • During cruise, maintain a steady engine speed between 1400 and 4000 rpm.
  • At idle speed, keep the throttle closed and the gear selector in the Neutral position. Remember, these are just the preliminary instructions. The actual drive cycle must conform exactly to the following instructions, or the various monitors may not run to completion.
  • The drive cycle begins with a cold engine startup. The IAT must be between 32 and 85 degrees F. Engine Coolant Temperature (ECT) must be less than 127 degrees F. It may be necessary to leave the car with you overnight so it can cool down completely. The engine coolant and intake air temperatures must be within a tight range to complete all of the OBD II monitors during the drive cycle. If the IAT input is not between 32 and 86 degrees F at the beginning of the drive cycle, the EVAP monitor will not run.
  • Start the engine and allow it to idle in Park for one to two minutes.
  • Within the first minute and a half, accelerate at 1⁄4 to 3⁄4 throttle to 50-55 mph. Hold that speed for 2-3 minutes. Unless your shop is very close to a major expressway, it may be difficult to satisfy this step in the drive cycle.
  • Decelerate to 0 mph without braking, then idle for 1-2 minutes. If you’re on an expressway, pull safely off the road during this segment.
  • Accelerate to 55 mph, using 1⁄4 to 3⁄4 throttle, then hold a steady cruise for 10 to 20 minutes.
  • Return to 0 mph with the engine idling in Park, then turn the ignition off.

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