# Code PO 171

**URL:** <https://community.cartalk.com/t/code-po-171/77400>\
**Category:** Maintenance/Repairs\
**Created:** [February 16, 2013, 9:12pm UTC](https://community.cartalk.com/t/code-po-171/77400 "2013-02-16T21:12:03Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Chey](https://avatars.discourse-cdn.com/v4/letter/c/e99b99/32.png) [@Chey](https://community.cartalk.com/u/Chey)\
**Post date:** [February 16, 2013, 9:12pm UTC](https://community.cartalk.com/t/code-po-171/77400/1 "2013-02-16T21:12:03Z")

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My 2006 chevy trailblazer is popping a code PO 171. i recently replaced the idle control sensor housing unit and after that is when this code appeared. i have replaced both O2 sensors and the air filter. Thinking that the new left O2 sensor was bad, i purchased a new one and plan to have that one put on. in the mean time while driving this week the check engine light went out for about half an hour, but then came back on and has remained on. Any ideas what else may be making it pop this code? Need your help. Chey

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**Author:** ![common-sense-answer](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/common-sense-answer/32/716_2.png) [@common-sense-answer](https://community.cartalk.com/u/common-sense-answer)\
**Post date:** [February 16, 2013, 9:40pm UTC](https://community.cartalk.com/t/code-po-171/77400/2 "2013-02-16T21:40:42Z")

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**_That’s One Of The Most Commonly Found Codes When The CEL Illuminates._**

[http://www.obd-codes.com/p0171](http://www.obd-codes.com/p0171)

Check the items listed here. Perhaps something was disturbed when the work was done.

_ **CSA** _

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**Author:** ![db4690](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/db4690/32/2583_2.png) [@db4690](https://community.cartalk.com/u/db4690)\
**Post date:** [February 16, 2013, 9:50pm UTC](https://community.cartalk.com/t/code-po-171/77400/3 "2013-02-16T21:50:00Z")

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@Chey let’s back up

P0171 lean code  
Vacuum leaks  
Low fuel pressure  
Exhaust leak in front of bank 1 upstream oxygen sensor

I think you should return those O2 sensors. By replacing those, you are shooting the messenger.  
They are in all likellhood only doing their job, reporting the oxygen content. The PCM then saw the excess oxygen and flagged P0171

Whoever told you to replace them doesn’t understand automotive emissions systems and shouldn’t be giving advice.

The first thing I would do is listen for any obvious vacuum leaks at idle. That means hissing.

Why did you replace the “idle control sensor housing”? It is possible that you created some kind of a leak when you did that. Perhaps you left something off/loose.

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**Author:** ![keith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/keith/32/5518_2.png) [@keith](https://community.cartalk.com/u/keith)\
**Post date:** [February 16, 2013, 10:59pm UTC](https://community.cartalk.com/t/code-po-171/77400/4 "2013-02-16T22:59:47Z")

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It can also be a dirty MAF sensor, easily cleaned with alcohol or a spray MAF cleaner.

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**Author:** ![circuitsmith](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/circuitsmith/32/40376_2.png) [@circuitsmith](https://community.cartalk.com/u/circuitsmith)\
**Post date:** [February 17, 2013, 1:38am UTC](https://community.cartalk.com/t/code-po-171/77400/5 "2013-02-17T01:38:40Z")

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Did you use new gaskets on the idle air control?  
Reusing an old gasket can result in a vacuum leak.