P0420 I am getting a MIL p0420 and don't know where the O2 sensor is.

Got it scanned and it's P0420: Catalyst efficiency below thresholdbank 1. They said it could be a bad catalytic converter or oxygen sensor. I borrowed a scanner and tried to measure the oxygen sensor readings over time.Sep 8, 2011


civic - Check Engine code P0420 Catalyst efficiency below ...

mechanics.stackexchange.com/.../check-engine-code-p0420-catalyst-efficie...
Feedback

P0420 Error Code: Catalyst System Efficiency Below ...

www.obd-codes.com/p0420
P0420 OBD-II Trouble Code. Technical Description. Catalyst System Efficiency Below Threshold (Bank 1). What does that mean? This diagnostic trouble code ...

P0420 Code Fix How Its Done Catalyst Efficiency Below ...

? 4:25
https://www.youtube.com/watch?v=-c8090n1Ihs
Jun 20, 2014 - Uploaded by ACE AUTOS UK
Here is a tutorial on P0420 code fix catalyst efficiency below threshold How To Diagnose a p0420 code ...

fault code that is set when the Onboard Diagnostic II (OBD II) system sees a drop in converter efficiency. The OBD II system monitors catalyst efficiency by comparing the switching activity of the upstream and downstream oxygen sensors in the exhaust. The upstream O2 sensor in the exhaust manifold reflects the condition of the exhaust gases as they exit the engine. The downstream O2 sensor in or behind the catalytic converter reflects the condition of the exhaust after it passes through he converter.

This code can be a pain... unfortunately P0420 means it could be several things. Depending on how old the car is...
- Check for exhaust leaks in all pipes and exhaust manifold (visual inspection, listen for that ******* noise evident of holes)
- Get an O2 sensor socket, remove the sensors and inspect. Peer inside the catalytic converter from top and bottom, look for clean horizontal honey comb pattern. Should be obvious if pieces are falling out. Look at O2 sensors for corrosion or fading of metal, they only last ~100K. Only the upstream sensor affects how the car drives though, the bottom one just measures how good the cat is doing. Either one can trip the check engine light though.
* Symptoms of driving performance may take awhile to develop, and either a bad sensor or bad cat can cause it to run rich and burn excess fuel. Running long times with a bad upstream sensor can lead to damage on the cat, so do the cheap O2 sensor replacement first.
[My 1998 civic had the light on since I got it in May, finally performance and fuel economy started dropping. Before buying an O2 sensor or new cat, I visually inspected everything and finally took the sensors out to look at them and inside the cat. The cat and bottom sensor looked okay, but the top was corroded (I figured it was the top since my driving was being affected). I replaced the top O2 sensor and she runs nicely now, I expect fuel economy to return. You can clean sensors sometimes (no water), but usually its corroded so just replace it. $70 for a sensor is WAY cheaper than paying someone to replace you cat, which is a recommended change if you end up having to get a new cat anyway (don't want to ruin a new cat with a bad sensor dumping fuel in).

If you need further help, I’m available over the phone at https://www.6ya.com/expert/david_4c166ba81493f541

P0420 - Catalyst System Efficiency Below Threshold Bank 1http://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.

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

The Cat is good,not if it is 12 years old

Only a select few last 14 years

O2 Sensors should be changed every 100,000 miles

Tune-up --- as in spark plugs?
No tune-up in my world, in the last15 to 20 years

ECM/PCM has been tuning all vehicles since 1980

An EVAP Code for a small leak or any evap issue,
obviously needs to be diagnosed & repaired within
a week,as you should with any OBD Codes,you don't
keep using the vehicle,you fix it

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

The problem is NOT the O2 sensor, this code (p0420) indicates: P0420 Catalyst System Efficiency below Threshold(Bank1)

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