2000 Mitsubishi Galant OBD Code PO421

skykings44 · Posted at Fri Jul 03, 2009 8:00 am

Engine Performance problem
2000 Mitsubishi Galant 6 cyl Front Wheel Drive Automatic 297000 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?

bluelightnin6 · Posted at Fri Jul 03, 2009 8:47 am

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 .

skykings44 · Posted at Fri Jul 03, 2009 9:21 am

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.

bluelightnin6 · Posted at Fri Jul 03, 2009 10:47 am

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.

skykings44 · Posted at Fri Jul 03, 2009 10:57 am

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.

bluelightnin6 · Posted at Fri Jul 03, 2009 11:00 am

Bank 1 refers to the passenger side of the vehicle...that is where the faulty O2 sensor is at.

skykings44 · Posted at Fri Jul 03, 2009 11:28 am

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?

bluelightnin6 · Posted at Fri Jul 03, 2009 12:03 pm

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.