How do I fix this?
The code is telling you there is a problem with the MAP sensor which measures vacuum in the intake and outside air pressure.
The sensor needs to be tested and possibly replaced.
SOURCE: replacing heater switch in 2004 hyundai sonata
Open the ashtray, and grab the bottom of the bezel. Its only clipped in, so give it a yank and the bezel will come off. Unplug the connectors and replace your switch.
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
SOURCE: hyundai sonata 4 cyclinder touble code P0171
Sometimes the mass air flow sensor will become clogged with some miniscule particles of dust or whatever else. When you open up your hood somewhere near where the air filter box is, there will be a hose running from that to the engine, the mass air flow sensor should be somewhere in near there. They are easy to remove and should be held in place with a few screws. Make sure not to touch any of the electrical connectors on the inside or allow them to get dirty. I used mass air flow sensor cleaner from the local parts place but it is a bit pricey. There may be some alternative cleaners available that are not as expensive. Take the sensor to a relatively dust free area and spray it all over with the cleaner and allow to dry. At the same time under the hood where the sensor was spray that area as well. Once the sensor has dried out re-install it and you should notice an improvement. If the problem still persists you may need to change your spark plugs, or spark plug wires.
SOURCE: Removal of Radio in 2004 Hyundai Sonata
Remove the facia plate, and remove the 4 screws that hold the radio in place. It's actually one of the simplest cars you can do.
SOURCE: how do you reset the check engine light on hyundai sonata?
Just disconnect your battery for a couple of minutes.
Please see my tip at http://www.fixya.com/cars/r5932051-check_engine_light_check. These are generic instructions. If you get stuck or need specific instructions for your car, please get back to me with model, year and engine info.
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