Question about 2002 Chevrolet Impala

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I have a 2002 impala it showing troubleshooting p0420 OEM brand: domestic. What is the major problem

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Could be intake gaskts leaking causing this or could be bad cat. convertor on bank 1 cylinder head, could be as simple as a bad spark plug causing that bank to run nonefficient. Bank 1 is the cylinder head that is the closest to you when standing on r side of car looking at engine (passenger side) you will see one head which is closer to you than the other...that is Bank 1

Posted on Feb 16, 2012

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I have 2002 chevy impala changed the 02 sensor and it is still reading the same 02 sensor.


because its not the sensor.
its the plug for the sensor .the wires.or it
is the cataletic converter/exhaust system
i just replaced my exhaust on my 07 chevy malibu same o2 sensor issue p0420 or something like that ?!
replace the converter and youll be fine i still have my old sensors in there that gave me the code :)
there not saying there bad but that the cat is bad.

Mar 18, 2015 | 2002 Chevrolet Impala

1 Answer

P0420 catalyst


Have it replaced by a qualified mechanic

Oct 04, 2013 | 2002 Chevrolet Impala

1 Answer

Check engine with code p0420


Generally, this code is from a failed converter. Most exhaust or diagnostic shops can perform a converter back pressure test to confirm if the converter is failing.


DTC P0420 - Catalyst System Efficiency Below Threshold (Bank 1)
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.

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 (HO2S), replace if necessary
  • Replace the catalytic converter

Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you're not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

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.


Hope this helps; also keep in mind that your feedback is important and I`ll appreciate your time and consideration if you leave some testimonial comment about this answer.

Thank you for using FixYa, have a nice day.

Jun 22, 2012 | 2002 Chevrolet Impala

1 Answer

2004 Chevy Impala SS 3.8L Supercharged: I am getting OBD2 codes P0171 (System too Lean (Bank 1)) and P0420 (Catalyst System Efficiency Below Threshold (Bank 1)). I also found an oil leak today. I...


for p0171, try:
In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
Inspect all vacuum and PCV hoses, replace if necessary
Check for a dirty fuel filter and proper fuel pressure
for p0420, try:

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

Aug 23, 2011 | 2004 Chevrolet Impala

1 Answer

Troubleshooting P0420 OEM Brand Honda A/F ratio concern Air leak near H2OS(heated oxygen sensor) Ignition system concern faulty catalytic converter


P0420 indicates the computer thinks the catalytic converter isn't working as well as it should. This is determined by the PCM evaluating the switch rate of the front and rear o2 sensors. Once the rear o2 sensor switch rate reaches a point close to the front o2 sensor it sets the code. This can be a result of degenerated catalytic converter, or in some rare instances, bad o2 sensors. In most cases repairing this condition requires replacing the catalytic converter with an OEM unit. Aftermarket converters don't have the same quality and quantity of the precious metals that make up the substrate found inside. This usually results in the code setting again in just a few months.

Oct 04, 2010 | Honda CR-V Cars & Trucks

1 Answer

Radiator fans fuses keep blowing-chevy impala 2002. we need info on following codes: P0108, P0128, P 0341, P 0401, P 0420, P 1480, and P 1481. John


p0108 map curcuit high input, p0128 coolant temperature below thermstat regulating tempurature, p0341 is camshaft position sensor A-bank 1 ckt range/performance, p0401 is exhaust gas recirculation, insufficiant flow detected, p0420 is catalyst system efficiency below threshold, p1480 is manufacturer control auxilary emission controls, p1481 is same as p1480.

Jun 15, 2010 | 2002 Chevrolet Impala

1 Answer

My catalytic converter is operating below factory recomendations, what needs to be fixed?


it was code P0420, this means the cat is worn out, they last about 100,000 miles in most cases, but it can vary allot

Mar 16, 2010 | 2002 Chevrolet Impala

2 Answers

Cant fill up gas 2002 hyundai sonata


have emission system checked or buy manual and perform test

Sep 19, 2009 | Hyundai Motor 2002 Sonata

3 Answers

2002 Toyota Solara p0420 code


it has to go to the dealership in california.

Jun 04, 2009 | 2001 Toyota Corolla

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