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Discussion Starter #1
Newbie to this forum,

I have a 2001 VW Jetta TDI with 186,000 miles. The check engine light comes on after driving one mile or more. I checked the ODB II, and received an error code of P0420. I had the motor replaced last year and it had the same error code before and after the swap. I replaced the EGR value and still the same problem. All help will be appreciated.
 

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Not sure but post moved to mk4 section since it's a specific technical question. Here is what ross tech's wiki says:

16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold

Possible Causes


  • Leakage in Intake and/or Exhaust System
  • Catalyst faulty
  • Oxygen Sensor(s) faulty
  • Oxygen Sensor(s) Control faulty
Possible Solutions


  • Check Intake and Exhaust System for Leaks
  • Check Catalyst
  • Check Oxygen Sensor(s)
  • Check Oxygen Sensor(s) Control
    • Perform Oxygen Sensor(s) Aging Check
 

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Discussion Starter #3
Thanks for information. I will check the catalyst. In the future I will try to post in the correct section.
 
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