# Service engine light



## 02 4X4 (Jun 4, 2005)

got a 2002 frontier the service engine ligh has been coming on and i ran a checker for codes and what i got was an emission system prob says catylast below threshold thats not being very specific has any one heard of this problem and what the more specific problem might be.


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## asrautox (Jan 6, 2006)

This usually indicates that either your rear o2 sensor is bad (the one after the cat), or your catyletic converter is gone. Hope that it's the first...


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## 02 4X4 (Jun 4, 2005)

asrautox said:


> This usually indicates that either your rear o2 sensor is bad (the one after the cat), or your catyletic converter is gone. Hope that it's the first...



Kewl thanx how do i know if the o2 sensor is bad? Or do i just have to replace it and hope for the best


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## asrautox (Jan 6, 2006)

Have you noticed a decrease in performance or mileage? Is there a bad or different smell to your exhaust? If the answer is yes to either or both, it's probably your cat. If not, it's most likely your o2.


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## 02 4X4 (Jun 4, 2005)

asrautox said:


> Have you noticed a decrease in performance or mileage? Is there a bad or different smell to your exhaust? If the answer is yes to either or both, it's probably your cat. If not, it's most likely your o2.


I have'nt noticed running any different or anything like that no drop in mileage either


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## Char (Jun 16, 2005)

If youre friends with a mechanic they can always check the resistance on it to see if its gone bad. You may be able to do it yourself if you know what numbers you need.


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