Question about 2002 Pontiac Firebird

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Service engine light comes on , p0420 code

Changed both after cat 02 sensors. after 120 miles, service engine soon light came back on , only 42,000 miles on car. Is the cat bad?

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  • hawkeye774 Apr 19, 2009

    p0420 code low cat emissions

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  • Pontiac Master
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The light can be caused by any one or combination of over 200 trouble codes, go to any kragen or Autozone parts store and ask for a trouble code test, it is free, then record the code(s) they come up with and post them back on fixya

Posted on Apr 19, 2009

  • yadayada
    yadayada Apr 19, 2009

    this code means the catalyst efficiency is lower than it should be, the most likely cause is a worn out cat converter.

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3 Answers

I have a p0420 code on my 2010 Jetta, already changed my 02 sensor. the car has only 70k miles on it, should I change the CAT or look at something else?


I wood look at somin else clear the code if it comes back then we should seewhat we can do as anything Changes since it has been on ? Let me Know thks for your time

May 10, 2015 | 2010 Volkswagen Jetta

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04 Altima 2.5 s w 150k changed cat 2014 1 yr later p0420 code again what r normal reads for 02 sensors? reads @ idle fluctuate @ .3V b1 sensor & .8V b2 sensor.anyone had p0420 that wasnt a bad cat


Those cars are notorious for engine problems unfortunately. The exhaust valves tend to warp from heat after around 200k miles. Therefore throwing the O2 codes. Best outcome and cost effective thing I can recommend is replacing the engine with a new or low mileage engine.

Feb 18, 2015 | Cars & Trucks

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I have a 2003 saturn ion 4 door, it has a ton of miles 194k. Last week the alternator went out do I replaced it without a problem, then the day after the check engine light came on I hook up the diagnostic...


p0420

no FSM> and not looking up P0420?
no engine stated, so ill get it wrong too..?????????????
420 is cat monitor failure. "efficiency"
the most hard of all.

ill make a list from hard and expensive .
1: bad sensor 2 rear. you failed to do both, that was WRONG.
2: bad cat. (i can weld on any cat for $99 bucks.) i do it last.. dead last.
3: engine running real bad. BUY a scan tool, now.

so the o2 is new that leaves #2 or #3.
i never shot gun cats. but shops do, its not their cash, huh?

i connect a real scan tool (not one that misses factory DTC codes)
then look at pendings for P042o , see funny sensor readings there, bingo.
i check every PID. for all sensors to be sure they READ right.
ECT AT 180F+ AND HOLDING? HOT.>?,
is the engine holding closed loop status at idle, no fix that NOW.
is LTFT (long term fuel trim ) near 0 or at - 40 or + 40% (fix that next)
if trim is good, the engine.
If the front 02 is new, the AFR will be correct and the the front 02 will swing fast and the trim will be near 0 , -4 is near best.
tad rich , natural.
once the engine is running Stoich at light flat cruise. (close loop) the
cat will heal its self (bake dry) and stop throwing 420. ( a hope deal)
if not the cat is bad.

ive cured some of the most hard 420s,.

on some ratty engines, a new cat can in fact hide it , until it cooks to death and next year 420 are back.
id never do that because gas is expensive. fix engine first.

Jun 24, 2014 | Cars & Trucks

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Readings on my 2003 Toyota 4 cylinder ck engine soon is P0128, P0420, P0430.. what could it be. Should I change thermostat, 02 sensor or catalytic converter.. Please advise.


PO128 = It is probably a bad ECT (engine coolant temp) sensor. PO420= The problem could be a bad cat, o2 sensor (Pre- and/or post cat)or o2 sensor wires, or an air fuel mixture problem that has caused the cat to fail.PO430= Catalyst System Efficiency Below Threshold (Bank 2) Your CAT converter is not cleaning properly. Hope this helps, James Booth

May 17, 2011 | Toyota Highlander Cars & Trucks

2 Answers

PO420 code-service engine light is on


P0420 Catalyst System Efficiency Below Threshold (Bank 1) first thing to do is go back to basics do a tune up (plugs) check the plug wires spray them with water or windex if you get a miss change them, run some fuel injector cleaner through it, don't just throw parts on it ,that is'nt cheap

Mar 24, 2010 | 2002 Nissan Altima

2 Answers

Service engine light comes on code is p0420


That code means that the catalytic converter is operating below it's threshold of efficiency. It could be that the cat is clogged which would necessitate getting a new one (the car would run terribly with almost no power) but more often than not the post-cat oxygen sensor is failing. That's the one between the cat and the muffler. Its only purpose is to serve as a comparator against the readings from the primary (pre-cat) sensors, to determine whether the car is working correctly. I'd change that, clear the code, and start driving to see if it comes back.

Feb 03, 2010 | 2000 GMC Jimmy

1 Answer

Code p0420


Hello.

Normally, the P-0420 indicates a sensor issue; a cat replacement would be needed if you had the P-0420 coupled WITH a
P-0430 code.

What I would do, if I were you, would take the car to a shop that can perform an "induction cleaning", and have that service done. Then, replace the spark plugs, if the car is around 90,000 miles. You may alsop need a front air-fuel sensor (the one on the manifold) replacement.

I would not change the cat until I did the above services. It does not sound like a bad cat just yet.

Dec 30, 2009 | 2004 Toyota Corolla

3 Answers

Receiving engine code p0420 on my 2005 altima 2.5 s


A p0420 code indicates a Catalytic System efficiency failure, Bank 1.
Basically, the computer is seeing reduced efficiency of the catalytic converter or one of it's components (such as an 02 sensor)

There may be a few root causes, such as a faulty oxygen sensor, faulty coolant temperature sensor, faulty converter, Large exhaust leak, or retarded (slow) timing.

Nov 30, 2009 | 2005 Nissan Altima

1 Answer

'02 civic engine code P0420. What does this mean?


it means your 02 sensor pre cat is not working or the cat is no longer any good start with the 02 sen its easy to do and cheaper than the cat

Feb 19, 2009 | 2002 Honda Civic

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