so my girlfriend just bought a used 02 jetta with only 50k miles on it. its a 4 cylinder, but the thing eats gas like crazy. the check engine light is on intermittently for P0420 (catalyst efficiency). does anyone have any ideas as to what could be going on with the gas mileage?
It could be a few things like a MAF sensor being bad, but if i would check with it throwing that code would be to see if the engine temp sensor was bad and giving a colder reading making the engine run rich, that would make the cat code throw on some cars but not sure on the vw, but if u can get a scan tool that can check the outputs it should read normal engine temp, if you cant get one idk how you would check it, the other thing to check would be if the thermostat was stuck open and its not getting hot enough and the engine runs cold, that will make it run rich, that would be the road to travel down first, but dont just start throwing parts at it until u know for sure good luck
Sounds like that code means its a bad O2 sensor. Try to give it a tune up also.
if the car was actually running rich, it would more than likely set an 02 sensor code, and if it was the MAF or the ECT, it has it's own separate codes, the problem is probably the 02 sensor after the catalytic coverter, or the catalytic converter is actually damaged, that can be caused by running cheap fuel or E85.
idk about the 4 cyl but the vr6 has truble with the coil pack and it will sort out makin it run rough and will set off the check engine light whick will flash (meaning according to the manual that theres a problem with the cat). just another possibility. if that is it it can be fixed for a few bucks with adheasive.
I had the same engine light reading, i changed out the easy o2 sensor and it has not kicked back on. for that reading. also beware of the coil packs they like to burn out too,
As others have relayed to you,you need someone with a good scan tool that can monitor several different functions,MAF readings,comparisons between the front and rear O2 sensors as well as engine and intake air temperature readings,if a scan tool is available that can also check to see if a cat efficiency test can be run,this will give an idea if the cat is good or not.Too many variables to nail this without a good scan tool and the interpretation of the information the scan tool gives you.My best answer for you is to find someone that specializes in VW repair and is up to date knowledge wise,stay away from the free analyzation places,most of those places are simply parts changers,they will keep on going until either you or they run out of things to change and your wallet is a lot thinner.
HI You should check the exhaust catalyst converter if gets plug up the engine will b hard on gas. And can run hot.
Check the throttle body assembly as well.
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