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Old 02-08-2009, 12:35 PM   #1
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Unhappy Cel codes P0171, P0174

Mine's an '03 with 50k miles. I have a rough idle, cel on with trouble codes P0171 and P0174. I have replaced the MAF to no avail. Any insight?
Thanks

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Old 02-09-2009, 03:19 AM   #2
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Join Renntech.org

But until you do, this is what I found:

P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 - Above Limit
P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 - Above Limit

Good luck
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Old 02-09-2009, 08:10 AM   #3
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Originally Posted by vath2001
Join Renntech.org

But until you do, this is what I found:

P0171 Oxygen Sensing Adaptation, Idle Range, Bank 1 - Above Limit
P0174 Oxygen Sensing Adaptation, Idle Range, Bank 2 - Above Limit

Good luck

Thanks for researching Renntech; I'll join. The AutoZone guys read the codes as 'both banks running lean' and the most probable cause the MAF sensor. $285 later for a new MAF sensor and I still have the problem. Is it possible that the oxygen sensor on both banks would go bad simultaneously?
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Old 02-09-2009, 09:58 AM   #4
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Maybe. Have you tried resetting the CEL. Drive it and read it when / if the CEL comes back.

When the CEL comes on, is it always the same codes? Or do they change every time?

O2 sensors are about $150 each from Porsche. I've seen them for $25 each on E-Bay... but no idea of how good they are.
And you have 4 O2 sensors (before and after each Cat).
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Old 02-09-2009, 11:14 AM   #5
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Originally Posted by vath2001
Maybe. Have you tried resetting the CEL. Drive it and read it when / if the CEL comes back.

When the CEL comes on, is it always the same codes? Or do they change every time?

O2 sensors are about $150 each from Porsche. I've seen them for $25 each on E-Bay... but no idea of how good they are.
And you have 4 O2 sensors (before and after each Cat).

I have had the codes read twice. Advance Auto read them as P0171, P0174 and turned off the CEL. Two days later it came back on so I had AutoZone read them. Same codes showed and they also turned off the CEL. After it came back on I cleaned the MAF with electrical contact cleaner and reinstalled, disconnecting the battery before removing it. The CEL light was off for a time because I had disconnected the battery, but came on again a couple days later. This time I replaced the MAF after disconnecting the battery. The light is now out, but the rough idle continues and I expect the light to come back on at any time.

Would I not get codes against the O2 sensors if they were bad?
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Old 02-09-2009, 11:50 AM   #6
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Same code I get but only on Bank 1. When I clear it the code comes back in a couple days max. However my car runs fine.

Based on discussions I've had with my shop the MAF is most likely if it is both banks. With only 1 we are looking to other sources including exhaust leaks and the O2 sensors.

However you have already changed the MAF to no avail. I would next do the O2 sensors.

See the thread on cracked headers in the general discussion forum. If it is running that rough you might want to look some other things over and make sure you don't have any undue air getting into the system.
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Last edited by schwank; 02-09-2009 at 11:53 AM.
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Old 09-25-2012, 05:59 PM   #7
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Green03, I know an old thread, but these are the exact codes that are showing up for me and will reappear after a few days if I clear it.

What did you do to resolve this issue?
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Old 09-25-2012, 06:16 PM   #8
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Quote:
Originally Posted by green03 View Post
Mine's an '03 with 50k miles. I have a rough idle, cel on with trouble codes P0171 and P0174. I have replaced the MAF to no avail. Any insight?
Thanks
I just ran into the same codes on my Expedition. In my case it was cause by a vacuum leak between the PCV valve and the throttle body. I'd check for vacuum leaks before spending a bunch of money on sensors. It's unlikely both sensors are bad.
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Old 09-25-2012, 06:41 PM   #9
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Quote:
Originally Posted by green03 View Post
I have had the codes read twice. Advance Auto read them as P0171, P0174 and turned off the CEL. Two days later it came back on so I had AutoZone read them. Same codes showed and they also turned off the CEL. After it came back on I cleaned the MAF with electrical contact cleaner and reinstalled, disconnecting the battery before removing it. The CEL light was off for a time because I had disconnected the battery, but came on again a couple days later. This time I replaced the MAF after disconnecting the battery. The light is now out, but the rough idle continues and I expect the light to come back on at any time.

Would I not get codes against the O2 sensors if they were bad?
"rough idle continues" may be the key. I don't believe a bad MAF causes rough idle. most likely vacuum leak in the intake manifold.
I'm with Schwank and Foydawg, try looking for vacuum leak before more replacing part$$
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Old 09-26-2012, 04:37 AM   #10
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Almost defiantly a vacuum leak. I've never done it but I believe you'll want to find someone to do a smoke test presuming you can't find an obvious leak (which I suspect is pretty damned hard in a Boxster).
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Old 09-26-2012, 10:51 AM   #11
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Almost defiantly a vacuum leak. I've never done it but I believe you'll want to find someone to do a smoke test presuming you can't find an obvious leak (which I suspect is pretty damned hard in a Boxster).
I think you're absolutely right... Here's some videos I found incase anyone else has these exact same codes...

Smoke testing for codes P0171 P0174 - YouTube

SMOKE WIZARD Finds Vacuum Leaks! 1-888-668-6080 - YouTube
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Old 09-26-2012, 11:22 AM   #12
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Thanks for the link to the video. I'ld only ever heard of a smoke test and never actually seen one.

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