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I can smell bad carbon smoke and also reading Code PO420. What can it be? Bad O2 Sensor or Broken Gasket Seal or Bad Cat? I have a 1998 740il....

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  • OBD II P0420-
    • Catalyst System Efficiency Below Threshold Common Problems That Trigger the P0420 Code
      • Inefficient Catalytic Converter(s)
      • Defective Front or Rear Oxygen Sensor(s)
      • Misfiring engines
        have a good day !!

Posted on Mar 26, 2011

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Service engine soon light is on showed p0160 replaced an checked for bad wiring to the mas air sensor still rough idle in gear n now want to shake when it shifts into overdrive it shakes


MOST LIKELY A BAD O2 SENSOR...Potential causes of an P0160 code include: Holes in exhaust near post cat o2 sensor Bad Bank 2, position 2, o2 sensor Wiring problem, melted harness, broken connectors, etc. Bad PCM

Apr 16, 2015 | 1996 Chevrolet Suburban

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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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Code po420 on scan tool but o2 sensor was replace 2 months ago


Hello and welcome. the code P0420 is for a bad cat. converter. replacing 02 sensors wont repair this code. the code simply's means that thje cat. converter is not working as designed and will need to be replaced.

The PCM determines the oxygen storage capability of the catalytic converter has degraded below a calibrated threshold.

Jul 03, 2010 | 2004 Mazda RX-8

2 Answers

Code P0430 Truck has a bad pinging upon acceleration. Originnaly gave me a 0300 code. Changed plugs wires and fuel filter. Still has a bad pinging and loss of power. at 111,000 miles am going to try...


p0300: random multiple cylinder misfire detected.
p0430: catalyst efficiency below threshold bank 2

This can be a hunt and seek game here... the EGR valves on these can create havoc on the v/8 try removing it and checking it for being stuck open/clogged with carbon etc. be sure you have a new gasket when removing it, its critical to engine idle/performance.
Try taking it to an Auto Zone Parts Store and let them run the scanner on iot for free they will give you a print out and advise if that helps and its all free.

May 06, 2010 | 1998 Chevrolet K1500

1 Answer

2001 Tacoma running rich but the scanner is reading a lean code


No, disconnecting the sensor and seeing no change would be a indication the maf was bad. Your computer takes information from your mass air flow sensor (maf), o2 sensor, cam position, and knock sensor to regulate the correct mixture. I would suspect a bad o2 sensor upstream. Try taking off the o2 sensor and seeing if there is black carbon on the base of the o2 sensor. If it has black carbon on the base it could be a bad o2 sensor. This problem could also be easily solved by hooking up a mechanics diagnostic computer to pin point the problem. Sometimes, you can clean the mass air flow with a special cleaner to help it generate a more accurate reading.

Apr 20, 2010 | 2001 Toyota Tacoma

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

1 Answer

Nissan fronteir codes are P0420, P0430 what has failed


po420 and430 is telling that the catalyst converters are no good both, most of the time bad o2 sensors maake computer think cat is no good, the way it tests is if o2 sensor reading before cat is about the same as the one after cat computer asumes cat is not bruning exhaust good , iwould replace o2 sensors reset check engine light and go from there, that might be the problem,if you were to replace cat o2s should be done at that time,so do o2s first,good luck.

Nov 05, 2009 | 2003 Nissan Frontier Crew Cab

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PO420 Catalyst System Efficiency below threshold.


Basically the mechanic will make sure don't need a tune up. or have vacuum issues or leakes in the exhaust before the cat. Then he should check the front 02 sensor to make sure its not getting lazy. If all this passes then you will need a new cat. If the O2 sensor has more than 70,000 miles on it it needs to be replaced anyways so you may just want to do this first and hope the light stays off.. The problem with a lean code is you will wear out the cat real fast if you didnt deal with this and kept driving the car. The lean code could have been vacuum leak or a bad MAF sensor or weak fuel pump.

Sep 02, 2009 | 1999 Mercury Mystique

1 Answer

PO420 CODE CAT EFEC


this can usually be set due to front O2 sensor malfunction
even though reading from front O2 sensor looks normall and not setting a code, its not reading correctly replace the front O2 sensor

Jun 26, 2009 | 2004 Isuzu Rodeo

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