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2003 Honda Accord Engine Malfunction Light

Tiny
WISDOKE2233
  • MEMBER
  • 2003 HONDA ACCORD
  • 4 CYL
  • FWD
  • MANUAL
  • 120,000 MILES
Eng Malfunction Light keeps coming on from time to time. I replaced the lower O2 Sensor about a year ago.

It comes on from time to time for a day or two and then goes off. However, its now been on for two weeks. I had AutoZone clear all of the codes and it came back on within a day.

Had it read again this moring:

P0420
Catalyst system efficiency below threshold bank 1
Probable Cause:
aa1 A/F ration concern
aa2 Air leak near HO2S (heated Oxygen sensor) bank 1
aa3- ignition system concern
aa4- faulty catalytic converter

Not sure where to go. Like I said, I did the O2 Sensor about a year ago and within 3-4 months the light was coming back on for a day or two.
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Monday, January 18th, 2010 AT 9:35 AM

1 Reply

Tiny
MMPRINCE4000
  • MECHANIC
  • 8,549 POSTS
Start by checking fuel pressure with a mechanical gauge, incorrect fuel pressure will cause air/fuel ratio problems.

Next, If you can remove convertor (bolted on) remove and visually inspect convertor, if you see any melted material or cracks, then convertor is problem.
If you cannot remove convertor, have a backpressure test performed, high convertor backpressure indicates a clogged convertor.

Also inspect exhaust system near or in front of O2 sensor for exhaust leaks.
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Monday, January 18th, 2010 AT 11:04 AM

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