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Anonymous Posted on Jun 01, 2014

My check engine light came on, checked with scan tool came up with a code P0420?

5 Related Answers

Anonymous

  • 1077 Answers
  • Posted on Mar 24, 2009

SOURCE: Code P0420

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

There is one 02 sensor in front of the catalytic converter (called upstream), and one behind it (downstream). When the engine is warmed up and running normally the upstream oxygen sensor reading fluctuates and the downstream one is fairly steady. In the case where both readings are fairly steady, a P0420 check engine light code is set.

Possible Causes:
Oxygen (O2) sensor not working correctly
Damaged or leaking exhuast (pipe, manifold, catalytic converter)
Damaged catalytic converter

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Anonymous

  • 3 Answers
  • Posted on Mar 28, 2009

SOURCE: Scan tool will not erase code # P-0601/2001 chrysler sebring 2.7

Sounds like a bad PCM.A dealer may be able to reflash the thing but not certain.Do a web search for the above code and you'll get all kinds of info. Good Luck

Anonymous

  • 295 Answers
  • Posted on Jul 07, 2009

SOURCE: 1999 Honda Odyssey p0420 Error Code

Cat efficentcy. replace the converter.

brandon_m618

Brandon Miller

  • 63 Answers
  • Posted on May 04, 2010

SOURCE: check engine light p0300, p0420 & mtv solenoid makes noise

P0300
1.ignition system fault spark plug ign wire coil.
2.vacuum leak, inj fault.
3.high or low fuel pressure.
P0420
1.catylist eff low bank1- cat can be defective.
2.eng misfire, vacuum leak.
3.engine oil leak into the exhaust valve guide seals.
as for the warranty i dont know.

airjer995

Jeremy W.

  • 5332 Answers
  • Posted on Oct 23, 2011

SOURCE: cod p0420

P0420 is a catalytic converter inefficiency code. Basically the cars computer is looking at the rear O2 sensor to monitor the catalytic converters ability to properly reduce emissions. If the computer sees the rear O2 sensor acting differently than normal it interprets this as the cat no longer able to do its job and turns on the check engine light to make you aware there is an issue. There are a few things that can cause this to happen. The most common is that the catalytic converter has gone bad and needs to be replaced. The good news is the federal emissions warranty on these is typically 8 years or 80,000 miles. Sometimes longer if the manufacturer chooses. If you fall into this guideline call you local dealer and see if you are covered. If you are you will be able to have this replaced at no charge. The bad news is if you are not covered than you will have to pay for it out of your pocket and they are not necessarily cheap. Do not go with anything but either the o.e. cat or a direct fit from a put able supplier. Anything other than these two options will leave you with more problems than they solve. Let me know if you have any questions and I'll do my best to answer them. Thank you for using FixYa.com!

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

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2003 Saturn stopped running on the Highway?

Question edited for clarity.
Question moved to maker category. Always include MODEL.

The key to your issue is the Check Engine Light. A Scan Tool will tell you EXACTLY what the trouble it. I will give a DTC Error Code, with a 'P' and 4 numbers. like here

https://www.google.com/search?q=saturn+vue+dtc+p0420

..
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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.
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The check engine light and VSC light came on in my 2005 highlander. 168,000 miles

P0420 & P0430 You need new catalytic converter
The P0430 check engine light code, like P0420, means the catalyst system efficiency is below the required threshold. Simply put, this means your car is adding more pollution into the air than it's supposed to.
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P0420

Hi Osar-
I pulled this link from ODB-codes.com. It lists the possible causes, diagnostics and resolution for engine code issues. Hope this helps!
P0420 OBD II Trouble Code
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2000 Ford Taurus code p0420

Well it depends on what the actual problem is.
Code 420 means the catalytic converter is not working as well as it should be.
The computer uses data from the front and rear O2 sensor to gauge the operation of the cat.
The problem could be the cat, or something else in the exhaust system, or one of the sensors.
A mechanic would check the temp of the cat and watch the data flow coming from the sensors with a scan tool.
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2000 outback check engine light on all the time, changed front o2 sensor, changed fuel cap, unplugged battery, and none turn this light off.\r\n any suggestion?

You have to hook an OBD 2 scan tool up to the data link connector and check to see what code is present. If you have a knock sensor code, you need to replace the knock sensor. If you get a P0420: Catalyst system efficiency below threshold, you will need to replace your catalytic converter. But if it is nothing important, the only way to clear a check engine light is with a scan tool. You can usually go to any aftermarket parts store and they will check and clear you codes and light for free. I hope this info helps.
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I have a 2001 chevy S-10 2.2 liter. What does Code P0420 mean??

here are a number of things that could be causing this p0420 catalyst efficiency code. The most common thing is the catalytic converter itself is no longer functioning properly.
The other likely thing is the rear O2 (oxygen) sensor is no longer working properly. Other things could include exhaust leaks, damaged exhaust pipes, damaged O2 sensor wiring/connectors, plugged catalytic converter, etc.
The easiest thing to do first is a visual check of things. Visually inspect the exhaust system for leaks, check the catalytic converter for dents, holes, severe discoloration, and check for a rattle inside. If any of those syptoms are there, the converter likely needs replacement.
Then, visually inspect the downstream O2 sensor (behind the converter). Check for broken wires, obvious faults, etc. If all that checks out, you'll want to check the operation of the O2 sensor. To do that, you'll need access to a scan tool or oscilliscope. Check that the waveform is pretty steady. If the reading fluctuates then the sensor is likely bad and will need to be replaced.
Try this, turn the ignition key to the on position, (engine not running) and pull the fuse to your ECM for 30 seconds and then re-install it. Once re-installed, start the engine and let idle for 1 min and then go for a test drive.
If the engine stalls, let it. The ECM is relearning the sensors and engine, just restart it and after 1 min when the RPM drops. God for a test drive and see if the service engine light comes back on and re-scan for the DTC codes and address the issues indicated by the DTC code.
Thank you for using fixya and good luck.
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