Question about 2001 Hyundai Sonata

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Check engine light .The engine codes I get are P0421 and P0171.

My 2001 Hyundai Sonata hesitates upon acceleration.especially when departing from say stop signs. once I get on highway and hit cruising hwy. speed it runs smoothly. This is what I've done so far:
The mileage on the car is 129,335 miles.
2.I changed the spark plugs about 7 months ago.
3.I changed the fuel filter 6 months ago. It was super dirty!
4. The air filter is only 2 months old.
5.changed the upper oxygen sensor about 1 month ago.
These changes did help get me better gas mileage but not get rid of check engine light or hesitation when accelerating.

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6 Suggested Answers

6ya6ya
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Posted on Jan 02, 2017

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sleepygsx
  • 98 Answers

SOURCE: 2001 hyundai sonata 2.4 dohc, cylinder 3 misfire code

tried testing the igniter also i would look into the injector, that will cause a single cylinder misfire and probably is your problem?misfires are not noticeable at higher speeds, which im sure you know but i would go that route, could have a pinched injector or a stuck one. one easy way to test is swap 3rd injector with another and see if that one starts misfiring instead, another rought is to get a cheap auto stethoscope and put it to each injector to hear if its opening and closing, compare with others. good luck.

Posted on Dec 11, 2008

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dealt_soul
  • 296 Answers

SOURCE: engine code p0421

Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold
/ catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings


To Do list

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

Posted on Jan 19, 2009

  • 1 Answer

SOURCE: My 2002 Hyundai Elantra Gt (2.0L)engine runs rough

The Hyundai online shop manual and my newly arrived Hyundai shop manual kept pointing to the coil as a possible problem. While preparing to check coil continuity I discovered the pigtail connected to the bottom of one of the coils was loose and the contacts were burned. This is the coil that supplies spark to plugs 1 & 4, the same ones that kept showing up each time the check engine light illuminated. After cleaning the contacts and making sure the pigtail was securely attached to the base of the coil I have had no further problems.

Posted on Jun 15, 2009

  • 14 Answers

SOURCE: 2000 hyundai accent hesitates when

inlet manifold either loose or gasket blown

Posted on Aug 20, 2009

buckway2222
  • 6 Answers

SOURCE: Acceleration Issue

your fuel injectors are clogged

Posted on Aug 23, 2009

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Engine code p0421


Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

A code P0420 may mean that one or more of the following has happened:

* Leaded fuel was used where unleaded was called for
* An oxygen sensor is not reading (functioning) properly
* The engine coolant temperature sensor is not working properly
* Damaged or leaking exhaust manifold
/ catalytic converter / exhaust pipe
* Retarded spark timing
* The oxygen sensors in front and behind the converter are reporting too similar of readings


To Do list

* Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
* Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
* Inspect the downstream heated oxygen sensor (HO2), replace if necessary
* Replace the catalytic converter

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