Question about 2003 Nissan Se R

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My 51 plate 1.8 Tino shows code po420 all the time. My code reader can cancel it,but it returns.I have replaced the front o2 sensor, and the cat, and the timing chain and plugs and coil packs recently. It uses rather a lot of oil. Where do I go from here?

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  • combensl Sep 14, 2010

    Cannot quite see why the heading will not alter from "2003 SEr", but there you are!
    Thought it might be a duff cat, and have complained to the supplier, and will go on with that if necessary.
    CO figure is .290 on a MOT limit of .300.
    Temp guage stays solid on halfway up. Have tried cataclean, which resulted in the mil coming on after 60 miles instead of 20, so I assumed she was fouling up somehow, and I was starting to suspect valve stem oil seals. She pulls well, does not smoke, and does 37mpg. My codereader will cancel the code ok, but I wonder if the car has to go through some particular stopstart cycle to reset the ecu. Any ideas?



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Your right as the 420 code refers to the cat, not being able to clean the exhaust your smoking problem has to be fixed to fix this code as the code is the cat can't clean up the exhaust enough. You may do an expensive oil change and see if you can reduce the smoke enough that the cat can clean the exhaust. STP or other stop smoke product and freash castrol 20-50 and even flushing the oil out with a flush additive. Then the reason the code sets is the rear cat is switching more than once in fives times of the front one. this could also happen if the car doesn't hit full operating temperture. ( middle of the gauge) the therostate may not be letting the car warm up all the way and then the fuel turns up higher and the smoke tand the inability for the engine to go into a proper closed loop. In worm summer operation the car should warm up to the middle of the gauge and stay there as you drive ( not go down as you speed up) if it does the therostate is bad and with the right one and a good oil change or two you may fix it. It's also possible that it's run too cool for too long and the only way to fix it is to rebuild the engine or get a good used one installed.

Posted on Sep 14, 2010

  • John P Schwantes Jr Sep 16, 2010

    Yes the car does go though a start stop sequence. the car has to warm up all the way go into closed loop and stay there for a minute or more but it sounds like the car is burning too much oil to get the mixture right if it's not leaking and it goes less than 500 miles on a quart of oil your going to have to do somehting about the oil burning. wanta play a game with the computer? It won't hurt it and it sounds like you have your own code reader. Find the plug for the rear oxagen senser, With it unpluged with the key already on or even running drive the car and see if the check engine light comes on.. They don't sell your car in the USA so i'm guessing. You may find it runs just fine with it unplugged or you get a O/2 senser heater code. If you do figure out witch wire is the senser wire and remove it from the plug and plug the heater wires up. ( their usally the same color) let the senser wire hang. then drive it and see what happens. You can trick it to thinking everthings OK. make sure that the wire doesn't get in troble as you may decide to fix it right later, and an inspector may look and call you down for it. theirs noone watching the emmissions parts here where I live but they check all over the place and they may check wher you live and in some cases the safty lane may fail a car with the check light on. Be careful and have fun.


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If there is oil consumption,this may be the problem,the o2 is sensing the oil ,and is trowing the code,this is a oil usage problem.The engine is burning engine oil.

Posted on Sep 15, 2010


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