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cel code p0171

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Old Feb 1, 2010 | 06:00 PM
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Default cel code p0171
I have a 01 a4 1.8t with 124k miles and the check engine light came on with error code p0171. Anyone know what this is? I just replaced the turbo and all vacuum lines looked fine, what else can cause this? Thanks
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Old Feb 2, 2010 | 07:57 AM
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P0171 System too Lean (Bank 1)

Possible fixes I can quickly think up are O2 sensor, MAF sensor or Coolant temperature sensor. Ideally have it scanned by a vagcom unit for a more detailed explanation.

If you don't have access to a vagcom I'd switch out the coolant temp sensor and clear the code, see if it comes back. The CTS works with your fuel trims based off of engine warmth so it may not be reading correctly.

A new CTS isn't costly and is an easy replacement: Click here for a new CTS
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Old Feb 2, 2010 | 07:58 AM
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oops, duplicate*
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Old Feb 3, 2010 | 12:29 PM
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hey thanks for the reply, my car never seems to warm up all the way unless im sitting in traffic would this also be a symptom of a bad coolant sensor? It stays from 1/4 to 1/3 on the temp gauge.
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Old Feb 3, 2010 | 12:33 PM
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Originally Posted by teabagger
hey thanks for the reply, my car never seems to warm up all the way unless im sitting in traffic would this also be a symptom of a bad coolant sensor? It stays from 1/4 to 1/3 on the temp gauge.
Actually it may be somewhat unrelated and a second issue in general. If you aren't getting to temperature your thermostat is probably sticking open, letting your coolant flow to much and thus keeping you and your engine too cold. It isn't a hard job on the 1.8t at all, plenty of DIY's out there.

This is a super common problem in Audi's and VW's. Click here for new thermostats.
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Old Feb 20, 2010 | 11:18 AM
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hey got the sensor thanks, for the install my manual and a write up i read says to remove a ring around the sensor and it should come out, i dont see the ring is the 01 a4 different than the other b5's? thanks again
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Old Feb 22, 2010 | 07:14 AM
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All the models should have O-rings, it would be news to me if they did not. It may be stuck on the sensor or in the hole still.
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Old Feb 22, 2010 | 11:50 AM
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My 01 1.8t is throwing this same P0171 code intermittently. Would the CTS be a possible cause of the intermittent light?
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Old Feb 22, 2010 | 12:04 PM
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Possibly yes, the CTS is a common failpoint and does engage this code. Also, typically related faults include a dirty MAF or a dying o2 sensor.
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