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Failed emmisions with high nox. level did not change after…

Customer Question
Failed emmisions with high...

Failed emmisions with high nox . level did not change after new cat installed

Mechanic's Assistant: What is the model/year of your Subaru?

2002 outback 2.5 engine

Mechanic's Assistant: How many miles are on the car? Is it an automatic or a manual transmission?

179,000 automatic

Mechanic's Assistant: Are you fixing your Outback yourself? What have you tried so far?

New cat new rear o2 ran bg 44k and a tank of 93 octaine

Submitted: 11 months ago.Category: Subaru
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Answered in 5 minutes by:
7/28/2017
Subaru Mechanic: Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems replied 11 months ago
Chad Farhat
Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems
Category: Subaru
Satisfied Customers: 5,637
Experience: Owner at Carolina Auto Service & Sales , 20 years experience in Foreign & Domestic vehicles
Verified

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

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Subaru Mechanic: Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems replied 11 months ago

hey how are you

What are the fault codes retrieved ?

Please let me know

Thank You

Chad Farhat

ASE Certified Technician

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Customer reply replied 11 months ago
no codes present hc was .0824 limit is 1.2 co was .7380 limit is 15.00 nox was 5.2583 limit is 1.5
Subaru Mechanic: Mike V., Subaru Technician replied 11 months ago
Mike V.
Mike V., Subaru Technician
Category: Subaru
Satisfied Customers: 27,534
Experience: Certified Subaru Technician, factory trained by Subaru.
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HI nox is usually the result of a lean condition. This can be caused by vacuum leaks or an issue with the front O2 sensor. That being said, I have also seen egr valves stick open a bit and cause the lean mix. It is possible to have some kind of timing issue or valve issue ( carbon on the valves) cause this problem as well. Most of the time however it's either an egr problem or front O2 sensor problem.

I have seen a lot of front O2 sensors fail without storing a code.

Please let me know if there is anything else I can do to help.
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Customer reply replied 11 months ago
car does not have an egr valve and no vacuum leaks
Subaru Mechanic: Mike V., Subaru Technician replied 11 months ago

I guess that leaves the front O2 sensor, fuel pressure and last but not least the timing or carbon on the valve issue. Lean fuel mixture is what is going to produce high nox.

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Customer reply replied 11 months ago
all that was checked by subaru they said replace cat and rear o2. i quess i will take back to them
Subaru Mechanic: Mike V., Subaru Technician replied 11 months ago

The rear O2 sensor won't cause the lean fuel mixture problem. It's the front one that does the majority for the fuel trim. When you have high nox you basically have an issue with the combustion chambers running hotter then they should. This is caused by a lean fuel mix of gas and air. That front O2 has the most to do with that.

Please let me know if there is anything else I can do to help.
Just Answer does not compensate me for my time and resources, so please rate my answer by using the stars at the top of the page. Payment for your question includes any follow-up questions you may have. Free trials and subscription questions still require ratings.
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