2004 Volkswagen Passat PO421 Bank 1

Tiny
RSM
  • MEMBER
  • 2004 VOLKSWAGEN PASSAT
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 134,000 MILES
Hello,

Check engine light has been coming on and turning itself off for the last few months. It is steady, not blinking. I was told if it blinks that the converter has failed. I have notice no deterioration in performance or fuel economy. Is there a way for a relative novice to check the 02 sensors, for a fouled plug, the converter to diagnose this problem? Thanks,

RSM
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Sunday, November 23rd, 2008 AT 4:52 PM

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Tiny
RASMATAZ
  • MEMBER
A code P0421 may mean that one or more of the following has happened:

The catalytic converter is no longer functioning properly
An oxygen sensor is not reading (functioning) properly
A sparkplug is fouled up

You might want to have the exhaust gases checked before and after the catalytic converter to rule out a defective converter-inspect spark plugs-measure the oxygen sensors switching activity

Possible Solutions Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you're at it.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into
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Sunday, November 23rd, 2008 AT 6:23 PM
Tiny
RSM
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Thanks for your prompt reply. Could this be caused by the need for a software upgrade? Engine specs are V6 30 Valve 2.8 Liter.
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Sunday, November 23rd, 2008 AT 6:44 PM
Tiny
RASMATAZ
  • MEMBER
Have the oxygen sensor checked and tested its sensing that the ctatalytic converter is malfunctioning-
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Sunday, November 23rd, 2008 AT 6:51 PM

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