Question about 2002 Nissan Altima
HI. This is a sign of a catalytic converter that is not working as efficiently as it should be. It is part of the vehicle emissions system. 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 O2 sensor waveform readings should fluctuate, but the downstream O2 sensor reading should be fairly steady. If the PCM detects that the two O2 sensors are reading in a similar manner, the DTC code P0420 will be issued. The necessary action are to check for any exhaust leaks at the manifold, pipes and catalytic converter. You will also need to check the spark timing to insure that it is normal and inspect the coolant temp sensor for its integrity. If all the check points test out ok, the remaining actions will be to replace your catalytic converter. A lot of the emission parts are covered under the warranty package if the vehicle is not out of its warranty contract. If you still have full warranty coverage at this time, this repair should be covered. I would check that out before purchasing any parts.
Posted on Aug 24, 2010
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Posted on Jan 02, 2017
SOURCE: want to change the O sensors
I would definitely go with the Bosch brand and there are only two oxygen sensors. One before and one after the catalytic converter. As far as how hard they are to change out I don't know on your particular vehicle. Here in the states you can borrow a tool from your auto parts store to help you take it out but I don't know if that would be available to you. I just did the sensors in my father's Isuzu Trooper with a 22 mm wrench. If you can get access to them, they are easy to change. Just unscrew and screw them back in.
Posted on May 18, 2009
SOURCE: vsc and check engine light is on
DTC P0420: Catalyst System Efficiency Below Threashold (Bank 1)
The ECM uses sensors mounted before and after the three-way catalyst (TWC) to monitor its efficiency. The first sensor, and Air Fuel ratio (A/F) sensor, sends pre-catalyst A/F ratio information to the ECM. The second sensor, a heated oxygen sensor (O2S), sends post-catalyst information to the ECM. The ECM compares these two signals to judge the efficiency of the catalyst and the catalyst's ability to store oxygen. During normal operation, the TWC stores and releases oxygen as needed. The capacity to store oxygen results in a low variation in the post-TWC exhaust stream as shown below.
If the catalyst is functioning normally, the waveform of the heated oxygen sensor slowly switches between RICH and LEAN. If the catalyst is deteriorated, the waveform will alternate frequently between RICH and LEAN. As the catalyst efficiency degrades, its ability to store oxygen is reduced and the catalyst output becomes more variable. When running the monitor, the ECM compares sensor 1 signals (A/F sensor) over a specific amount of time to determine catalyst efficiency. The ECM begins by calculating the signal length for both sensors (for the rear oxygen sensor, the ECM uses the output voltage signal length). If the oxygen sensor output voltage signal length is greater than the threshold (threshold is calculated based on the A/F sensor signal length), the ECM concludes that the catalyst is malfunctioning. The ECM will turn on the MIL and a DTC will be set.
Hope this helps :)
Posted on Oct 19, 2009
P0420- Catalyst System Efficiency Below Threshold Bank 1
- Three way catalyst converter Bank 2
- Exhaust tube
- Intake air leaks
- Fuel injectors may be faulty
- Fuel injector leaks
- Spark plugs may be faulty
- Improper ignition timing
- Engine Control Module
The most common cause is the three way catalyst converter Bank 1. Changing just the O2 sensor usually don't repair the problem.
A three way catalyst converter(Manifold) with high oxygen storage capacity will indicate a low switching frequency of heated oxygen sensor 2. As oxygen storage capacity decreases, the heated oxygen sensor 2 switching frequency will increase.
When the frequency ratio of heated oxygen sensors 1 and 2 approaches a specified limit value, the three way catalyst (Manifold) malfunction is diagnosed.
Posted on Jan 26, 2011
SOURCE: Check engine light comes on
p0420 is set when the convertor is unable to store oxygen in the minerals used in the convertor. the lack of oxygen to mix with the exhaust gases causes the O2 sensor to set the code. if the O2 sensor has been replaced the only other thing to do is replace the convertor. you can check with the Subaru dealer and let them run your VIN to see if you had one of the defective convertors.
Posted on Aug 01, 2011
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