Question about 2000 Hyundai Sonata

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My Check engine light will not stay off long enough to get it inspected 2 codes pop up after every reset they are P0125 and P0171 I have replace Catalytic Converter and o2 censor reset the computer an about 10 miles down the road the light comes back on PLEASE HELP

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The best thing to do is, remove and clean all the sensors and connectors I have listed below.

A code P0125 may mean that one or more of the following has happened:

  • Insufficient warm up time
  • Low engine coolant level
  • Leaking or stuck open thermostat
  • Faulty coolant temperature sensor
Possible Solutions The simplest thing to do is to reset the code and see if it comes back.
If the code comes back, the problem is likely going to be the result of the above causes (faulty thermostat, faulty ECT sensor, or a low coolant level).
Other ECT sensor and circuit related DTCs

A code P0171 may mean that one or more of the following has happened:
  • The MAF (Mass Air Flow) Sensor is dirty or faulty
    Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
  • There could be a vacuum leak downstream of the MAF sensor
  • Possible cracked vacuum or PCV line/connection
  • Faulty or stuck open PCV valve
  • Failed or faulty oxygen sensor (bank 1, sensor 1)
  • Sticking/plugged or failed fuel injector
  • Low fuel pressure (possible plugged/dirty fuel filter!)
  • Exhaust leak between engine and first oxygen sensor
Possible Solutions A lot of times, cleaning the MAF sensor and finding/fixing vacuum leaks fix the problem. If you're on a tight budget, start there, but that may not be the fix for certain. So, possible solutions include:
  • Clean the MAF sensor. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
  • Inspect all vacuum and PCV hoses, replace/repair as required
  • Inspect all hoses and connections in the air intake system
  • Inspect and/or test the intake manifold gaskets for leakage
  • Check for a dirty fuel filter and proper fuel pressure
  • Ideally you'll want to monitor short and long term fuel trims using an advanced scan tool

Posted on Oct 27, 2012


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Posted on Jan 02, 2017


SOURCE: No pick up after 45 mph

it could be in a limp mode which would explain it not going over 45mph even though you replaced o2 sensor you may still have to take it to maindealer to reset brain memory.

Posted on Feb 22, 2009

  • 776 Answers

SOURCE: Check engine light comes on stays on for several

What is 'cadalis' code? ... catalytic converter efficiency below threshold? If so, it's not the O2 sensor. The converter is worn out if the code is catalytic converter efficiency. Sorry, expensive repair.

Posted on Jun 06, 2009

  • 1187 Answers

SOURCE: check engine light but no fault codes

Take the Accent to AutoZone. They will scan the code (free) and give you a print-out with a "general" explanation (free). They can also reset it properly.

Let us know the codes and a summary of the print-out. We will advise you.

Answers to your questions:
The sensors at the cat are O2 (Oxygen) sensors.
Problem could be the cat or could be a faulty sensor. My money is on the O2 sensor.

Could be lots of things, like sticky fuel injector...
Don't change the catalytic convertor just yet.
My opinion is that the "shop" doesn't really know and is hoping that replacing the cat will fix it all (my opinion).

If you eventually change out the cat, go to a local muffler shop, not a national chain. They will do the same job for a lot less and not try to sell you other stuff.

Posted on Oct 01, 2009

Testimonial: "there are no fault codes! Reset yesterday only 20 miles so far so good"

  • 119 Answers

SOURCE: catalytic converter or oxygen sensors?

i would replace the oxygen sensor first as it is the cheapest and easiest

Posted on Nov 06, 2009

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How to repair P0125 for 2000 Mercury Mountaineer

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