Question about Pontiac Grand Am

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2001 Pontiac Grand AM, failed smog due to fault code: P0420 Cat efficiency below threshold (bank 1). Which 02 sensor is most likely the problem? Before or after the cat?

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I would renew trhe pair of them to be honest ,and if that didnt clear the emmisions then a new cat as well

Posted on Aug 19, 2010

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How do I troubleshoot code P0420 and pass emissions


code p 420 refers to catalytic converter system bank 1--efficiency below threshold ===causes--- catalytic converter,--wiring---HO2S 2 sensor
could be a bad HO2S sensor or a failed cat converter
try the sensor first as they are cheaper than a cat

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2004 nissan xterra run great for 12 miles then misfiring,cnt get over 45 miles an hour. codes p 0733,p0420,p0430,p0328 comes up. new wires,new cap,rotor spark plugs 6 months old timming belt 6 months...


code p0733 refers to gear 3 -incorrect ration===causes---wiring---TR sensor/switch--shift solenoids---transmission mechanical fault
code p0420 refers to catalytic converter system -bank 1---efficiency below threshold===causes--cat converter--wiring--HO2s 2
code po430 refers to cat converter system bank 2--efficiency below threshold===causes--cat converter--wiring ---HO2s 2
code p0328 refers to knock sensor (KS) 1 bank 1--high input===causes--wiring short to positive--KS incorrectly tightened--KS---ECM

basically replace the cat converters as they are blocking the exhaust system and preventing your over 45mph problem
replace the TR sensor/ switch as you have not mentioned a transmission problem
Rectify the problem with the KS as it controls the air/fuel mixture setting which contributes to the car getting hot.

Jan 12, 2014 | Nissan Cars & Trucks

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Trouble code po420 2007 solstice


P0420 - Catalyst System Efficiency Below Threshold Bank 1xicon.jpghttp://engine-codes.com/p0420.htmlForum CodePossible causes- Three way catalyst converter Bank 1
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module (ECM) Tech notes The most common cause it the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem. If the P0420 code is combined with other codes, try fixing the other codes first.

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1 Answer

Code P0420 on 2001 jetta


P0420 Catalytic Converter System -Efficiency Below Threshold (Bank 1)
Sounds like your flexible pipe from back of cat to exhaust is blowing so its losing exhaust between the two sensors

Apr 26, 2012 | Volkswagen Jetta Cars & Trucks

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My 2000 Toyo. Tacoma Prerunner TRD V6, truck Failed smog due to the part #3 Functional Computer Tests due to an erased MIL. But had passed the Visual Inspection, and Emissions. So i bought a Code reader...


there are 2 sensors in the system
one is a heated oxygen sensor (HO2S) in the exhaust manifold / pipe before the cat converter that reports the exhaust gas composition to the ECM so that fuel/ air ratios can be adjusted
if that one is faulty it is most likely the reason for running lean or rich
the second sensor is the oxygen sensor (O2) which is after the cat converter and reads the results of the cat converter cleaning the exhaust
you may have to replace both the sensors to get a clearance or replace the cat converter as well as the HO2S unit

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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)

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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.

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