2000 Mitsubishi Galant OBD Code PO421

Tiny
SKYKINGS44
  • MEMBER
  • 2000 MITSUBISHI GALANT
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 297,000 MILES
OBD Code PO421 is registering on my car. According to what I'd read it means the "Warm up catalyst efficiency is below threshold bank 1". I'm told that translates to the sensor behind the ccatalyst converter is not functioning properly. Is that something I can change myself or do I need to have a qualified mechanic do it?
Friday, July 3rd, 2009 AT 11:00 AM

7 Replies

Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
Replacing an oxygen sensor is fairly simple, you just need a few basic tools (jack, jack stand, ratchet etc.). Disconnect negative battery cable, raise vehicle safely then disconnect the electrical connection of the sensor and unscrew / remove sensor.
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Friday, July 3rd, 2009 AT 11:47 AM
Tiny
SKYKINGS44
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When this sensor is not working does it make the car run slugish? Is this the code that identifies the 02 sensor down stream past the Catlayst Converter going toward the tail pipe at the end of the car.
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Friday, July 3rd, 2009 AT 12:21 PM
Tiny
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A faulty O2 sensor will cause poor fuel mileage and maybe some sluggish times.

DTC P0421 applies to the warm-up catalytic converter on the 2.4L engines and the right bank (bank 1) of the 3.0L engines.
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Friday, July 3rd, 2009 AT 1:47 PM
Tiny
SKYKINGS44
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I have a 2000 Galant V6. Where is the right bank bank one, and is it something I can replace without taking it to a mechanic? Thanks for all your assistance.
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Friday, July 3rd, 2009 AT 1:57 PM
Tiny
BLUELIGHTNIN6
  • MECHANIC
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Bank 1 refers to the passenger side of the vehicle. That is where the faulty O2 sensor is at.
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Friday, July 3rd, 2009 AT 2:00 PM
Tiny
SKYKINGS44
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Does it matter that I have a california engine in relation to wear bank one is for OBD PO421 code. Is it something I can replace without going to a mechanic?
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Friday, July 3rd, 2009 AT 2:28 PM
Tiny
BLUELIGHTNIN6
  • MECHANIC
  • 16,542 POSTS
No, doesn't matter and you should be able to replace it yourself if you have basic mechanic tools (ratchets, jack etc.). It just disconnects and unscrews out.
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Friday, July 3rd, 2009 AT 3:03 PM

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