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I have a folkswagen Golf MKV 2005 model, i used torque to check what the yellow motor sign means, and this is what i received:

P2201 - Powertrain NOx Sensor Circuit Range/Performance bank1

P2096 - Powertrain Post Catalyst Fuel Trim System Too Lean bank1

what does these mean, and if something is broken, what can I change ?

does these affect the fuel consumption ?

Torque fault log


It has probably been like this since before last service and possibly eu control. Are there any android applications I can install to get better information? I am using VGate OBD2 tool

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what engine in your 2005 Golf? –  mac Oct 7 '13 at 15:21
    
also, both of these codes are emissions related, and the two codes may be symptoms of one root cause (NOx emissions do increase in a lean-burn situation). –  mac Oct 7 '13 at 19:45
    
@mac: it's a 1.6 engine, if thats what you asking for:), will this be expensive to repair? I have EU control following february, and wonder if this may make my car not pass ? –  Plastkort Oct 8 '13 at 6:23
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2 Answers 2

One of the first things to check for when you have a post cat bias towards lean is the operation of the front sensor, together with front sensor fuel trim. If the front sensor is not working correctly and the NOx sensor reports lean then your answer is to replace the front sensor (pre-Cat). If the front sensor is working OK, then you have a faulty NOx sensor. Before replacing the sensor, can you get a garage to check your NOx emissions on a repair grade exhaust analyser to confirm NOx readings. All of the above assumes no system damage and intact wiring. The NOx sensor comes with a built in module which is usually system tested.

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This would probably make your car fail.

As far as causes, well there's a lot. Anything from vacuum leaks, to air/throttle/fuel/exhaust sensors, bad catalytic converter, fuel pump, injectors... it will require some good study of engine performance data/graphs, most likely with a better, more specialized scan tool.

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The car definitely will not pass inspection with these error codes. Vacuum leaks may be a good place to start looking, or the mass airflow sensor. –  mac Oct 8 '13 at 16:27
    
from a quick google it could be exhaust leaks or catalytic converter –  im_a_noob Oct 8 '13 at 21:39
    
There are a lot of possible scenarios. You need to compare graphs of MAF, O2s front and rear, throttle position, etc. to try and identify (and yes if you know what you are looking at you can even narrow down vacuum leaks and exhaust leaks with these graphs) –  Drake Clarris Oct 9 '13 at 3:21
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