Question about 2003 Chevrolet Tahoe

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I have engine trouble codes P0420 and P0430 and my Tahoe has been dropping RPMs at low speeds for some time. Ideas on steps to address this and what type of problem I may be looking at?

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Posted on Jan 02, 2017

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SOURCE: P0420 and P0430

I have a P0420 code and it seems to be the cat needs replacing.

Posted on Jun 05, 2008

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motor1258
  • 6674 Answers

SOURCE: 1999 cougar diagnostic code p0430 and p0420

Failed or faulty oxygen sensor, or faulty catalytic converter. It's actually the oxygen sensor reading that the catalytic converter is not functioning properly & needs relacement. That's provided the oxygen sensor is not faulty, which personally, I'd go for that first.
Both would explain excessive fuel usage.

Posted on Jan 25, 2009

  • 104 Answers

SOURCE: code p0430 p0420

there is a update for the engine computer if you take it in to your toyota dealer they can do it for you. there is a campaign on this issue so its free of charge

Posted on Apr 27, 2009

  • 102 Answers

SOURCE: P0420 & P0430 codes 99 silverado

codes p0420 and p0430 are both post o2 sensors, the ones after the convertor, both sides if replacing

Posted on May 18, 2009

bschilz
  • 2049 Answers

SOURCE: check engine light-on OBD code's P0420 &

The codes are Catalyst System Efficiency Below Threshold (Bank 1)&(Bank 2).

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.

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
Some suggested steps for troubleshooting a P0420 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.

Posted on Oct 06, 2009

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Car sometimes will not start after sits for a day


Definition of Diagnostic Trouble Code P0420 Category: Powertrain Definition: Catalyst System Efficiency Below Threshold Bank 1Note: This definition of P0420 is applied to all manufacturers

Definition of Diagnostic Trouble Code P0430 Category: Powertrain Definition: Catalyst System Efficiency Below Threshold Bank 2Note: This definition of P0430 is applied to all manufacturers

As the code description implies the P0430 code means that the vehicle's control module has detected that the three-way catalytic converter is not working properly (is not as efficient as the factory is expecting). Replacing the oxygen (O2) sensors may sometimes fix the code, but in most cases the catalytic convert needs to be replaced to fix the problem. If the P0430 code is combined with other codes, try fixing the other codes first.

Jul 11, 2015 | 2006 Toyota Solara

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I get OBD codes P0420 and P0430



P0420 and P0430

P0420 means Catalyst System Efficiency Below Threshold, Bank 1

P0430 means Catalyst System Efficiency Below Threshold, Bank 2

It means that the O2 sensors are good, and the O2 sensors are telling you that your catalytic converter, in the exhaust system is not working fine, as its emissions are polluting the air too much.

The catalytic converter is part of the exhaust system. The way to test this part is by doing an emission test. The two OBD codes that you are getting are already a test telling you that the converter must be replaced, unless an emission test done at a garage says the opposite.

This kind of problem will trigger the check engine light, and your car will also waste too much fuel.
You also risk to get in trouble if the car goes through an Air Pollution control, as the car won't pass an emission test in this condition.

To conclude, the Catalyst System must be replaced, the O2 Sensors are fine.

This is a repair that should be done at a garage, however you can find DIY instructions here:How to Replace a Catalytic Converter or you can get more detailed instructions, and step by step illustrated procedure purchasing a repair manual.

on May 27, 2009 | 2003 Chrysler 300M

1 Answer

Code p0420


Just did the P0430,so here's the P0420 trouble code.Trouble Code: P0420

Catalyst System Bank 1 Low Efficiency

Possible Causes:


Air leaks at the exhaust manifold or in the exhaust pipesBase engine problems (i.e., high engine oil or coolant usage).Catalytic converter is damaged, contaminated or has failed.Continuous engine misfire conditions, or weak or low coil output.Front HO2S or rear HO2S is contaminated with fuel or moisture.Rear HO2S is loose in the mounting hole (check it for a leak).Front HO2S older (aged) than the rear HO2S (HO2S-12 is lazy).Click here to see.

Jan 16, 2013 | 2005 Buick LeSabre

2 Answers

My 1999 Chev Tahoe will not start - Has codes p0430 and p0420


Hi Charlie,
Diagnostic Test Codes (DTCs) P0420 and P0430 ar "Catalyst Efficiency" codes. These simply mean that the catalytic converters in your vehicle are not performing the way they should be. To fix these codes, you will most likely have to replace the converters. However, these codes do NOT indicate why your engine wil not start. There are many things that can cause an engine to not start. Many of which may or may not set fault codes. You need to determine if the engine is getting fuel and ignition first then go from there.

Dec 17, 2011 | 1999 Chevrolet Silverado 1500

2 Answers

P0420 & P0430 GRAND CHEROKEE LAREDO 2005 3.7L


Hi Rabih,

I hate to tell you this, but it is time to stick your hands DEEP into your pockets and get ready to spend the big bucks! Diagnostic Trouble Codes (DTCs) P0420 and P0430 are "catalyst efficiency below threshold" codes. The ONLY way to fix them is to replace your catalytic converters. If you also have any other codes, you must fix these FIRST, otherwise you will only destroy new converters as well.

Oct 30, 2011 | 2005 Jeep Grand Cherokee

1 Answer

Drive and idle is normal but suddenly check engine, pcs and vsc light come up. mechanic have checked. they said this car have few code. p0420, p0430, c1734, b2090, c1a40


ok lets do this in order
P0420 Catalyst System Efficiency Below Threshold (Bank 1) an o2 sensor bad usually before the Cat converter P0430 Catalyst System Efficiency Below Threshold (Bank 2) same thing but the sensor after the cat converter the c1734 people will say you need to replace a bad BCM, but don't,, once the O2 sensor problem is addressed , that code will clear , it has to do with the remote start b2090 has to do with power doors ,, this will drop off too once the system is rest , same with the last one you listed, If I was you I'd have the 2 O2 sensors checked, replace the bad one, or both, and have the mechanic clear all the codes, then recheck them

Aug 11, 2011 | Lexus LS 460 Cars & Trucks

2 Answers

I have p0420 on my 06 pont gp gt. it mostly comes on after I slow down after highway


Here is the trouble tree for that code it is most likely a bad cat but follow the trouble tree to see where it lead's you.
DTC P0420 or P0430

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection\Initial Inspection and Diagnostic Overview\Diagnostic Starting Point - Vehicle
* Review Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0420

* Catalyst System Low Efficiency Bank 1

Important: A new converter with less than 100 miles on it may set DTC P0420 or P0430 due to out-******* of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition. Hope this helps

Feb 01, 2011 | 2005 Pontiac Grand Prix

2 Answers

P0420 & P0430 codes 99 silverado


codes p0420 and p0430 are both post o2 sensors, the ones after the convertor, both sides if replacing

May 17, 2009 | 1999 Chevrolet Silverado 1500

3 Answers

P0420 and P0430


P0420 and P0430 are codes related to the catalytic converter effeciency. The catalyst will need to be replaced $$.

May 19, 2008 | 2000 Nissan Maxima

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