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P0420 wasnt catalytic converter or 02 sensors???

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Air flow meter.

Posted on Jun 03, 2009

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What does a diagnostic tool mean when saying "bank 1"...


It usually means the catalytic converter is not getting hot enough to function, but could be another issue. The sensor readings between the sensor before and the sensor after the cat are not within spec.
Bank one is the side with cylinder one, or the side with the catalytic converter.

Jul 25, 2014 | 2003 Buick Regal LS

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Trouble code p0420


The P0420 code means that the catalytic converter efficiency is below threshold. Since there are two oxygen sensors, above and after the catalytic converter, they together generate signals which are used to monitor the efficiency. However, if the catalytic converter is bad, the sensor after the converter will generate steady results, without any fluctuations.
You can replace the catalytic converter to overcome this problem. However, there are chances of the P0420 code to come up if there is any leak in the exhaust or the downstream o2 sensor (after the converter) is bad. Ideally, before spending on cat, you should try replacing the downstream sensor, which you can buy at low price from online stores like oxygensensorworld.com and also inspect for any small leaks in the exhaust system. Since the converter can cost you more, think of replacing it only if needed.

May 23, 2013 | Cars & Trucks

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I noticed my engine light came on and I had power loss trying to climb a hill. I got home and ran the codes and P0420 came up. So my question is was is P0420 code mean?


Catalyst efficiency below threshold bank one. This could be the 02 sensor behind the catalytic converter on bank one or the catalytic converter is not doing its job. The numbers have to be read to determine which is bad. The takes a hand held computer

Aug 23, 2011 | Dodge Ram 1500 Cars & Trucks

1 Answer

Getting OBD codes p0420 and p0430, how to fix these issue with my 2001 Audi A6


2001 Audi A6
EOBD code: P0420
Fault location: Catalytic converter system, bank 1 - efficiency below threshold
Probable cause: Catalytic converter, wiring, heated oxygen sensor 2 (downstream)

EOBD code: P0430
Fault location: Catalytic converter system, bank 2 - efficiency below threshold
Probable cause: Catalytic converter, wiring, heated oxygen sensor 2 (downstream)

Sep 14, 2010 | 2001 Audi A6

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Check engine light on. took the car to auto zone to put it on a scanner. trouble code p0420. catalyst system efficiency below threshold. probable cause; large vaccum leak, fuel system fault, ignition...


Diagnostic code produces P0420 catalyst system efficiency below threshold-Bank 1. Probable causes are listed as follows:
1-air leak in exhaust before rear 02 sensor, 3-Fuel system fault,
4-faulty catalytic converter.

May 31, 2010 | 2001 Nissan Altima

3 Answers

2002 mitsubishi lancer oz rally troubleshooting p0420


Code p0420 is 'catalyst efficiency below threshold'.

This could be caused by a bad catalytic converter but before dumping a ton of money on that I would suspect the after-cat oxygen sensor is getting lazy and setting the code.

Have the O2 sensors checked and replace if needed before suspecting the catalytic converter.

Good luck.

Feb 11, 2010 | 2002 Mitsubishi Lancer

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

2 Answers

Code p0420 appears what does it mean engine lite came on


P0420 Catalyst System Efficiency Below Threshold (Bank 1)

What does that mean? The catalytic converter has an oxygen sensor in front and behind it. When the vehicle is warm and running in closed loop mode, the upstream oxygen sensor waveform reading should fluctuate. The downstream O2 sensor reading should be fairly steady. Typically the P0420 code triggers the Check Engine Light if the readings of the two sensors are similar. This is indicative of (among other things) a converter that is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.


Symptoms You will likely not notice any drivability problems, although there may be symptoms.
Causes A code P0420 may mean that one or more of the following has happened:
  • Leaded fuel was used where unleaded was called for
  • An oxygen sensor is not reading (functioning) properly
  • The engine coolant temperature sensor is not working properly
  • Damaged or leaking exhaust manifold / catalytic converter / exhaust pipe
  • Retarded spark timing
  • The oxygen sensors in front and behind the converter are reporting too similar of readings
Possible Solutions Need a catalytic converter? Visit our catalytic converter shopping area for the lowest price on your replacement converter!
Some suggested steps for troubleshooting a P0420 error code include:
  • Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
  • Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
  • Inspect the downstream heated oxygen sensor (HO2), replace if necessary
  • Replace the catalytic converter
One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it's out of it's bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It's worth checking into.

Nov 03, 2009 | 2007 Chrysler Town & Country LX New Cars

1 Answer

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

Mar 24, 2009 | Chrysler Concorde Cars & Trucks

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