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After replacing the head gasket code P0171 appeared

Tiny
BCMULLEN95
  • MEMBER
  • 2012 TOYOTA PRIUS
  • 1.8L
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 205,000 MILES
I recently replaced the head gasket. No previous codes where present prior to the replacement of the head gasket. Now I show code p0171. Any ideas of how to best diagnose where I may have a leak or if it is the O2 sensor?
Monday, February 8th, 2021 AT 3:19 PM

7 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,179 POSTS
Hi,

The code indicates a lean fuel mixture. I have a feeling there is a vacuum line/hose that was missed.

Let's check for that first. Here is a link that explains how to find a leak:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Do this and let me know what you find.

Take care and God Bless,

Joe
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Monday, February 8th, 2021 AT 5:43 PM
Tiny
BCMULLEN95
  • MEMBER
  • 249 POSTS
Sprayed all the vacuum hoses and intake, no engine acceleration noticed.
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Wednesday, February 10th, 2021 AT 1:56 PM
Tiny
BCMULLEN95
  • MEMBER
  • 249 POSTS
I also have permanent codes P0300, P0301, P0302, and P0117. New spark plugs, new ECT, new Water pump, new thermostat, and new coil packs. Not sure if they have anything to do with the P0171. I plan on driving the car through a drive cycle to see if the other permanent code clear.
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Wednesday, February 10th, 2021 AT 2:00 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,179 POSTS
Hi,

A misfire shouldn't be a permanent code. Are you able to clear it? If so, clear all codes and drive it to see what happens.

Let me know what happens.

Joe
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Wednesday, February 10th, 2021 AT 6:42 PM
Tiny
BCMULLEN95
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  • 249 POSTS
I should take it out for a drive tomorrow. I will let you know what happens.
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Thursday, February 11th, 2021 AT 10:11 PM
Tiny
BCMULLEN95
  • MEMBER
  • 249 POSTS
Took it for a drive and it sound bad. It has a really rough idle. Could being off 1 tooth on the timing cause the same codes that I have regarding misfire?
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Friday, February 12th, 2021 AT 12:03 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,179 POSTS
Hi,

Could you record it running and upload it for me to hear? When you put things back together, are you sure timing was correct?

Let me know.

Joe
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Friday, February 12th, 2021 AT 3:27 PM

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