2002 Mazda 626 Check engine light with code P0421 goes on a

Tiny
SUNNY0219
  • 2002 MAZDA 626

Engine Mechanical problem
2002 Mazda 626 4 cyl Front Wheel Drive Automatic 97868 miles

Car: 2002 Mazda 626 LX 4cyl 2.0L

The check engine light with code P0421 goes on when the car run city miles, and goes off when running highway miles or higher MPH in city. I sent my car to an auto shop, and they said that I need to replace the CAT, which runs about $1000, because of some problems with exhaust system. But the car passed the emission test over 1 month ago, and oil change is needed now. If it's not the problem of the CAT, what are the other possibilities?
Thank you!

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Tuesday, July 8th, 2008 AT 5:26 PM

4 Replies

Tiny
KHLOW2008
  • EXPERT
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Hi sunny0219,

Check for vacumn leakages around the air intake hoses and manifold.

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Wednesday, July 9th, 2008 AT 12:08 PM
Tiny
SUNNY0219
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Thank you, KHLow2008.
If there is a leakage, should the air intake hose be replaced or something else should be replaced? Do you know how much to fix a problem like that?

I am a real idiot about cars.

Thank you!

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Wednesday, July 9th, 2008 AT 4:53 PM
Tiny
KHLOW2008
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  • 41,975 POSTS

Hi sunny0219,

If there is any leakage, you should try to stop it by any means that you deem fit.

Taping up, sealing, any way that can prevent the leak would do or replacement if repair is not possible.

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Thursday, July 10th, 2008 AT 6:15 AM
Tiny
SUNNY0219
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Thank you! I went to do an oil change on the car using my own oil filter and oil. The check engine light went off itself in 2 or 3 days after I did the oil change.

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Sunday, July 20th, 2008 AT 4:24 PM

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