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Doug, ASE Certified Technician
Category: Mitsubishi
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Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Galant GS The code PO421 Warm Up Catalyst Efficiency

Resolved Question:

The code PO421 Warm Up Catalyst Efficiency Below Threshold (Bank 1)(5). What kind of repairs am I looking at?
Submitted: 3 years ago.
Category: Mitsubishi
Expert:  Doug replied 3 years ago.

Doug C :

Hi,
Is this the 2.4L four cylinder engine?
Do you have your VIN available?

Customer:

No 3.8 6cyc, 4A3AB36S76E024653

Doug C :

Okay thanks, XXXXX XXXXX moment while I check a few things.... in the meantime do you know your current mileage (roughly)?

Customer:

51,000

Doug C :

Thanks

Doug C :

Just another few moments

Doug C :

Thank you for your patience.

P0421 and P0431 are fairly common occurrences on this vehicle. The codes are indicating a material breakdown of the catalytic converter on the firewall side (P0421) or radiator side (P0431) of the engine..............

Doug C :

What is happening is the air fuel readings are being taken in front of and behind each pre-cat, and the readings are not dis-similar enough to indicate that the catalysts are working properly. Because this is an emission failure, the light is turned on and these code(s) are set

Doug C :

The bad news here is that these are very expensive on this vehicle (several hundred dollars for the parts alone) due to the pre-cat converters being builtinto the manifolds. Labor is nothing to overlook either as the rear one (the one you have failing) is quite a bear to change as well...........

Doug C :

The good news is that the catalytic converter and pre-cat converters are covered under your factory warranty for 8 years or 80,000 miles, both of which you are well under

Doug C :

What you will need to do is contact your Mitsubishi dealer and have this repaired under your factory warranty which will incur no charge to you at all.

Doug C :

At the same time, if you have any other minor issues with the car you will want to bring it to the dealerships attention now, as your complete bumper-to-bumper warranty (5 year 60k mile) is in effect until July 9th of this year.... so time is getting close on the bumper to bumper coverage

Customer:

Thanks the news is not great but atleast I know where I stand.

Doug C :

It isn't terribly bad news.... you will be out of your vehicle for probably a day, but that is it. It takes about 2-3 hours to change this part out.

Doug C :

Again this will be at absolutely no cost to you; the vehicle is safe to drive in the mean time as well

Customer:

Thanks

Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 6600
Experience: Mitsubishi employed and Factory trained ASE certified technician
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Doug
Doug
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