# NOX Failure

**URL:** <https://community.cartalk.com/t/nox-failure/6286>\
**Category:** Maintenance/Repairs\
**Created:** [October 22, 2007, 3:58pm UTC](https://community.cartalk.com/t/nox-failure/6286 "2007-10-22T15:58:10Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![ZIPPYS\_HOME](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@ZIPPYS\_HOME](https://community.cartalk.com/u/ZIPPYS_HOME)\
**Post date:** [October 22, 2007, 3:58pm UTC](https://community.cartalk.com/t/nox-failure/6286/1 "2007-10-22T15:58:10Z")

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I have a 1992 Nissan Maxima GXE, the car failed NOX emissions with a 6.25 (allowable is 3.25). EGR functions, Replaced O2 sensor (still didn’t pass lowered to 5.25). I am looking for another direction to go in. Any ideas would be great.

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**Author:** ![castironman](https://avatars.discourse-cdn.com/v4/letter/c/2acd7d/32.png) [@castironman](https://community.cartalk.com/u/castironman)\
**Post date:** [October 22, 2007, 4:11pm UTC](https://community.cartalk.com/t/nox-failure/6286/2 "2007-10-22T16:11:38Z")

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Hello;  
high NOx: temperature at the combustion chamber too high.  
best case: lean mixture caused by a vacuum leak; bad spark plugs; ignition timing off; bad gasoline.  
worst case: bad egr valve or catalytic converter.  
Please post your results.

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**Author:** ![Loafer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/loafer/32/28_2.png) [@Loafer](https://community.cartalk.com/u/Loafer)\
**Post date:** [October 22, 2007, 4:15pm UTC](https://community.cartalk.com/t/nox-failure/6286/3 "2007-10-22T16:15:18Z")

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I would have the EGR (exhaust gas recycle) system checked to make sure it is functioning properly. This is the primary NOx control for the engine. If this checks out then the next check is the catalytic converter. If the cat is original then it may be failing.

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**Author:** ![markmast](https://avatars.discourse-cdn.com/v4/letter/m/4af34b/32.png) [@markmast](https://community.cartalk.com/u/markmast)\
**Post date:** [October 22, 2007, 4:15pm UTC](https://community.cartalk.com/t/nox-failure/6286/4 "2007-10-22T16:15:42Z")

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You mention that the EGR functions. Are you sure that the EGR passages are open? Clogging is common.

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**Author:** ![ok4450](https://avatars.discourse-cdn.com/v4/letter/o/e9bcb4/32.png) [@ok4450](https://community.cartalk.com/u/ok4450)\
**Post date:** [October 22, 2007, 4:23pm UTC](https://community.cartalk.com/t/nox-failure/6286/5 "2007-10-22T16:23:19Z")

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How have you determined the EGR functions?

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**Author:** ![ZIPPYS\_HOME](https://avatars.discourse-cdn.com/v4/letter/z/ac91a4/32.png) [@ZIPPYS\_HOME](https://community.cartalk.com/u/ZIPPYS_HOME)\
**Post date:** [October 22, 2007, 7:25pm UTC](https://community.cartalk.com/t/nox-failure/6286/6 "2007-10-22T19:25:04Z")

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Hi,

Egr tested by: racing engine and verifying movement of diaphram, also if you attach vaccuum to the egr it causes the car to stumble. Also what would be any other signs of a bad catalytic.

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**Author:** ![americar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/americar/32/42_2.png) [@americar](https://community.cartalk.com/u/americar)\
**Post date:** [October 23, 2007, 12:39am UTC](https://community.cartalk.com/t/nox-failure/6286/7 "2007-10-23T00:39:25Z")

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I would check for vacuum leaks. BTW is the intake stock with no modifications