1998 Mazda MPV P0420 Check Engine Light

1998 MAZDA MPV

ROBHALE121971

MEMBER
1 POST

I own a 1998 Mazda MVP with 126,550 miles on it. The check engine light comes on for a day or two then it is no longer on for a while and will come on again. It's been doing this for a few months. I own a diagnostic code reader which has read PO 420 catalyst system efficiency below threshold (bank 1). I've noticed a smell of hot metal when I stop driving. I've read several of the posts concerning the check engine light on and the PO420 code. What is the most likely repair procedure required. It sounds like the O2 sensor should be checked/replaced and then possibly it may require replacement of the catalytic converter. I'm interested to hear what your diagnosis is based on the symptoms.

Dec 22, 2006 at 5:38 AM

RASMATAZ

✓Experienced Mechanic
75,988 POSTS

it sounds like you're on Track-keep it going

Dec 23, 2006 at 12:56 PM

COSMO

✓Experienced Mechanic
347 POSTS

Well if you are able to or know how....you need to monitor both front and rear 02 sensors for the front cat. 02s11 and 02s12 on your scanner (if you have one)....if both 02 sensors are fluctuating (when the engine if hot) at the same rate...you more than likely have a bad cat. If one 02 sensor (02s11) is fluctuating but the rear (02s12) is steady, than your cat is probably ok and will require some more diagnosis.

Cosmo...Mazda Tech

Dec 24, 2006 at 10:52 AM

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Suggested Repair

With the engine hot, compare the front and rear O2 sensors for the front catalytic converter (O2S11 and O2S12). If both fluctuate at the same rate, the converter is likely failing. If the front sensor fluctuates and the rear stays steady, the converter is probably okay and further diagnosis is needed.

Conversation Summary

A 1998 Mazda MPV with about 126,550 miles has an intermittent check engine light and code P0420, catalyst efficiency below threshold on bank 1, plus a hot-metal smell after driving. The owner suspected an O2 sensor and possibly the catalytic converter. An expert advised comparing the front and rear O2 sensor signals when hot: matching fluctuation points to a bad converter, while a steady rear signal means the converter is likely okay and more diagnosis is required.

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1998 Mazda MPV P0420 Check Engine Light

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