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Roy, import/domestic specialest
Category: Car
Satisfied Customers: 6195
Experience:  ASE master tech for 40 years
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2008 elantra with codes p0171 p0170 p0420 replaced rear o2

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2008 elantra with codes p0171 p0170 p0420 replaced rear o2 sensor and pulled out front o2 sensor and looked in converter not pluged

good morning my name is ***** ***** I will assist

the 420 is a cat code. the cat converter needs to be replaced. the precious metals are worn out and the converter is not doing its job anymore

171 is a lean code. possible causes are vacuum leak, mass air flow flow sensor, pcv valve or low fuel pressure from a bad fuel pump.


the 170 code is related to the 171 for fuel trim.


Customer: replied 1 year ago.

anyway to test convertor

you need a real scan tool to monitor the O2 sensors. comparing the 2 wave patterns will confirm. the fact that the code set is a 99.9% chance the cat is bad


please dont forget to rate me as it is the only way I get paid for my service


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