Hi l have scan my car /sonata/2006 . There is acode 504 what is mean

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All this means is that your car will not pass an OBD 2 emissions test.
P-powertrain
1-MFG: manufacturer specific
5- vehicle speed control and idle control system
07- Hyundai 07 fault code.

answered

code P0441 IS Evaporative Emission Control System Incorrect Purge Flow

code P0171 IS P0171 System too Lean (Bank 1

The Tensioner rod being replaced for $1,200 is a very good deal. Ihad mine done for $1,750 and I have been enjoying my car better since then.

I was advised to replace it or it might lead to a more severe issue as regards my 2006 Sonata.

Good luck.

sounds like a defective abs sensor in the car somewhere

"Fuel system too lean at idle". It's an air/fuel ratio that is not correct, possibly a vacuum leak somewhere. Or a leaky exhaust pipe. Could be related to intake manifold gasket. Somewhere, air is getting into the engine.

I suggest taking it back to the dealer under warranty. I think Hyundai is 10yr./100k for the original owner. 5yr./50k if not. Ask first if covered, and ask why not id not covered.

2006 Hyundai Sonata Service Manual is available here with diagrams and instructions.

It is a brake switch code, hyundai has posted a massive recall on them, though your car may not apply. It will need a switch, I think only 2 out of 500 have been a wiring issue.

If the light stays on and dosen't go out it means your air bag will not deploy in an accident. First thing to check is if the fuse is bad.