P0420 Code

[J-Rat]

I have a 2001 Nissan Altima SE with 97,000 miles... Engine runs great with no abnormal noises, missfires, or anything else. Service Engine light is on with code P0420.
I understand this could be the Catalatyic Converter. I also understand that the 01 Altima has two of them.
With the car running great could I still need to replace the C.C. ? If so which one? Any help is appreciated... Thanks !

[goofy123]

Hi,
I too had the P0420 error code until last week and was trying to find answers as I had no noticeable decrease in performance of my car. Finally I went through a set of steps to isolate the problem, I suggest the following steps:

1. Spray a can of carb cleaner all along the inlet right after the Mass flow sensor to the intake manifold while the car is idling. If you notice any change in idling then you have a intake leak. This will lead to the above code.
2. Check connections of front and rear O2 sensors
3. Check O2 connectivity with ECM (will give details of the ECM points later) - This is a rare case as if there is a loss of connectivity you would also have a O2 sensor code.
4. Sometimes if you have bad plugs or a leaking injector you may also get the code so check if you injectors are leaking by removing them, disconnecting the crank position sensor and turning the ignition to ON position, do not attempt to start the car.
5. Remove rear O2 sensor and start the car if it runs better than before it will mean your CC is plugged up and you need a new CC

Though I would recommend a factory replacement those are very costly you can try to get after market direct fits they run about $150.

Hope this information helps you out. Common problems are with the inlet manifold gasket leakage.

[NissanTech]

Excellent recommendations goofy123!

J-Rat, you should also try reprograming the ECM with the latest program before replacing any parts. The dealer can do that for your for around $100

[J-Rat]

Thanks guys. With the car running so good would you think it mosy likely will be just needing to be reprogrammed by dealer or something else?

On the O2 sensors. One is located underneath the car and the other is located just after the header before the first C.C. that is mounted vertical. Is this correct?

[NissanTech]

Thanks guys. With the car running so good would you think it mosy likely will be just needing to be reprogrammed by dealer or something else?

I would definitely start by reprogramming the ECM. There is a big chance that is the problem.

[mpe235]

I don't think there is an updated program for the 2001.

[J-Rat]

Anyone know if that is true? The dealer here in Norman, Oklahoma isn't the best to deal with.

[kll]

i have xtrail. i bought it as second hand last week. it has qr20 de engine similar to qr25.
when i bought it it has very very dirty engine bay, very dirty air filter old spark plugs etc.
I cleaned engine, sprayed brake pad cleaner into intake manifold by opening electronic butterfly by my hand gently, fittet everything back. installed a clean new filter. replaced oil. but not spark plugs.

i run car, there was normally smoke at pipe due to brake pad cleaner, then returned back to normal. i drove car for 10 km, suddenly MIL came, we checked code it was p0420. we cleared it. replaced spark plugs, it re appeared after 40 km. same code...

before cleaning, there were no check engine lights. i dont know about the past of this car well but i drove car for 50 km before i clean something there were no codes or lights, also performance was no good due to clogged air filter and old spark plugs with old oil. now performance is very good, no diling or stalling. no bad smell at exhaust.

it seemed idle speed is high, when in neutral it is 1300 rpm and when on D or R it is 900 rpm.

any comments? i remoeved rear oxygen sensor socket nothign happened. i will check voltage reading on sensors today. i do not want to decide on problem before diagnose porblem correctly.

cat is clogged? rear oxygen sensor after cat? idle contoller?

[NissanTech]

kll, try disconnecting the car battery for about 30 minutes to reset all systems.

[kll]

i did . no luck. there i no cat inside i guess. i checked both voltage reading on pre and post sensors on exhaust manifold. both gave similar reading and values are almost identical. it seems it was clogged and they removed it before i purchase the car last week. or it is there but cracked and sit on the bottom but not restricting flow.

i need to find aftermarket cat. but it seems i will need time. how can we turn off light?
by moving rear sensor up with an adaptor? or if i move sensors to bottom, on second catalytic converter will it work?

emission regulations are not strict here yet. so it can save time, until i find a converter.

[streamcast]

KLL: Check the ecm grounds on the engine. I think they are located on the right side of the engine/head to the rear of the engine. Sometimes they will loosen and cause this problem. Seen it happen before.

[deeznuts]

If you measured both the front and rear oxygen sensors and their readings were almost identical or close to it, cat is bad. Moving the rear sensor won't help either. It's sole job is to monitor cat efficiency. In other words if it was good both sensors would be reading completely different from one another. If you want to get rid of the light without converter replacement, you've got about two options. Remove/tape over the bulb, or install a rear o2 simulator.

[kll]

guys i managed to turn of MIL light.

i made a machine shop to prepare an adaptor for rear o2 sensor. i installed sensor with adaptor. adaptor is almost 4 cm long and screwed to original hole of o2 sensor. then sensor fits on the adaptor. now sensor is getting less gas flow on it, i measured readings and saw that it is around 0.4 volts when engine is idling. and changing when revving up. seems my readings are between factory specs for second sensor.(described on FSM)

we cleared code and now it is almost 800 miles after this operation, no lights :)

highly suggested simple method. better than taping the light, without any electronic overrides.

http://www.energeticforum.com/renewa...n-foulers.html

here is how they do with stock foulers. in contrast of this i did mine as a custom adaptor.

[Altimate_Suz]

I also have the P0420 code appearing. However, I'm using about a quart of oil every 1000 miles or so, and it's dirty as hell really quickly after an oil change. Car performs like a champ though. My last oil change (by my usual Valvoline guys), they tell me the coolant is testing unsafe, but when he brings the tube over to show me, it acts sort of okay. He tells me that I should watch the car for it getting hot and if it continues, I should have the coolant system flushed. I replaced the head gasket last summer and had my mechanic flush the coolant then.

Since that last oil change, I am noticing the metal pinging when I shut off the car. I only drive a half hour to work, and the engine sounds really hot. Still the car runs great.

???

Every mechanic friend I talk to just says they don't know what to think about that. Any opinions here?

[kll]

there is a recall for xtrail about catalytic convertor issue. and i dont know why but results are poor performance and broken CAT. if there is excess heat, that can damage components of your engine such as gaskets.