Check engine light problems...

CHEVROLET IMPALA
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MELODY7844
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  • 1 POST
I have a 97 Honda civic and my check engine light come on a few weeks ago. So I got the codes back from advanced autozone:

p0420 Catalyst Efficiency below threshold
p0302
p0303 Cylinder misfires
p0304

I'm assuming and hoping that I just need a tune up with replacing of the spark plugs, etc. As far as I know it's been a while since they've been replaced. Anyone have any advice or other ideas? I would appreciate it.

Oh and should I completely refrain from driving the car until it's fixed? That's my big question right now, since I'm uncertain what all that means.

Thanks
Jan 7, 2006 at 3:48 PM

What to check next

Diagnostic guidance. Suggested checks and possible repairs are separate from the owner's reported results.

Have the misfires diagnosed before deciding whether the catalytic converter needs replacement. If the engine light flashes or the engine runs severely rough, stop driving and arrange assessment.

Guidance references and applicability

Source: This question and its visible discussion. Owner reports are distinguished from other participants' experiences. Follow-up guidance is not a confirmed diagnosis. HELLA: Ignition-coil diagnosis https://www.hella.com/techworld/uk/technical/car-electronics-and-electrics/check-ignition-coil/ General ignition diagnostic background, not specifications or a component diagnosis for this vehicle.

Read the replies · Discussion summary and reported outcome

AI-ASSISTED GUIDANCE · REVIEWED BY 2CARPROS
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JEREMIAH
  • ✓Experienced Mechanic
  • 217 POSTS
changing the plugs,caps and rotors USUALLY clears the problem.how many miles do you have on it?
the other code means your catalytic converter is no good. it's a pretty expensive part.check with your dealer/s if they could warranty it for you.
i wouldn't advise driving around with three misfires though,and not changing the cat conv would fail emission inspection.
Jan 8, 2006 at 8:34 AM
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THECHEESEMANNN
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i would put a bet on faulty sensors. but if it has over 120000 miles, new plugs and wires would probably help gas mileage anyway. if the car studders alot when you romp on the gas, or if it just dies ad random, check the fuel pump, and the fuel injectors may be bad. thats an expensive fix though.
Jan 13, 2006 at 8:02 AM
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DAVAGIRL
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if you car has less than 80,000/8 years on it, then you can get Honda to fix that part for you for free! (catalytic converter). I got them to do my 2000 Passport. it was a $2000 job.
Mar 30, 2006 at 2:55 PM
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JEREMIAH
  • ✓Experienced Mechanic
  • 217 POSTS
the p0420 could also be caused by the misfire,since the oxygen sensor could be sensing the unburned fuel from the 3 misfiring cylinders which would cause it to think that the cat is bad.
Jan 18, 2008 at 12:21 AM
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Suggested Repair

Address the misfires first by replacing the spark plugs, distributor cap, and rotor, and avoid driving while three cylinders are misfiring. Recheck the P0420 catalyst code afterward, because unburned fuel from the misfires can make the oxygen sensor indicate a bad converter. If P0420 remains, have the catalytic converter inspected and ask the dealer about any remaining emissions warranty.

Conversation Summary

The owner of a 1997 Honda Civic reported a check engine light with codes P0420 (catalyst efficiency below threshold) and P0302, P0303, and P0304 (cylinder misfires), hoping a tune-up would fix it and asking whether the car should still be driven. An expert said plugs, cap, and rotor usually clear the misfires, advised against driving with three misfires, and noted the catalyst code can indicate a failed converter or be caused by unburned fuel from the misfires. Other commenters suggested sensors, plugs and wires, fuel pump or injectors, and possible catalytic converter warranty coverage.

Discussion summary

Check engine light problems...

A 1997 Civic had reported codes P0420 and P0302, P0303 and P0304. The owner asked whether a tune-up was needed and whether it could be driven. Replies initially focused on the converter, then considered the misfires.

Reported outcome: No completed repair or post-repair code check was reported.

The code list alone did not confirm a failed converter. The discussion's warranty statements and suggested parts were not verified for this vehicle.

Read the original discussion

AI-ASSISTED SUMMARY · REVIEWED BY 2CARPROS
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