Question about 1999 Chevrolet Silverado 1500

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P0420 & P0430 codes 99 silverado

I have a 99 silverado1500 4.8L and im getting codes P0420 and P0430? i was told it was my o2 that needed to be replaced, but theres 4 of um 2 (pre&post)on each side. how do i know if im replacing the rite one?

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

Posted on May 18, 2009

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I replace all three o2 sensor and still get p0420
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Posted on Jun 24, 2010

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Error codes


Christopher, BMW P0430 code catalyst efficiency fault, the converter is no longer able to do its job and may need replace.
Check the attached links very informative, instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
JE Robison Service Bosch Car Service Specialists the blog Those dreaded...
P0430 Replace the O2 sensor
P0430 P0420 Catalyst inefficiency do have to replace cats E46Fanatics
P0430 OBD II Trouble Code

Jun 03, 2016 | 2004 BMW X3 2.5i

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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

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

1 Answer

P0420 & P0430


It is not an O2 sensor issue.

Mar 22, 2014 | 2005 Hyundai Tucson

1 Answer

P0420 p0430 p0750


Code 750 is a problem with one of the shift solenoids inside the transmission.
Code 420 is for the catalytic converter performance bank one and code 430 is the same thing for bank two. The codes mean the cat is not performing up to standards based on the data coming from the O2 sensors. Sometimes it a sensor problem, and sometimes its a cat problem or something in the fuel system.

Feb 11, 2014 | 2003 Lincoln LS V8

2 Answers

What can i do to fix p0420 & p0430 code.. 2005 ford expedition 5.4 ,,,, can you please tell me where is located p0010 code, A camshaft position actuator circuit/open bank 1... Same truck .. Thank you


p0420 and p0430 both indicate a clogged catalytic converter. 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. The p0010 indicates camshaft sensor. The camshaft sensor may be the main problem, as it will affect your timing and fuel/air ratio, which in turn can effect what your Oxygen sensors detect, throwing the p0420 and p0430.

Make sure your car is timed correctly by the timing chain/belt, reset light, then if it dont' solve the problem, change oxygen sensors, if those don't help, catalytic converter is clogged.

Dec 10, 2013 | Cars & Trucks

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

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

1 Answer

Ck. Engine P0420 & P0430


engine code p0430 for 2005 toyota sienna

Nov 25, 2009 | Toyota RAV4 Cars & Trucks

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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