Codes 171 and 174

2002 GMC SIERRA
142,000 MILES • 4.7L • V8 • 2WD • AUTOMATIC
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FOXDEN
  • MEMBER
  • 22 POSTS
code reader gives to codes 171 and 174. banks 1 and 2 lean. service engine soon light comes and goes. usually not on in warm weather. Truck will start in cold weather , but I have to keep giving it gas to keep it going until it warms up.
Jan 12, 2021 at 9:37 PM
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KASEKENNY
  • ✓Experienced Mechanic
  • 18,907 POSTS
More then likely you have a vacuum leak. Here are two guides that have really good info in them to help with this. Let's run through both of these to find out if any of this is the issue.

https://www.2carpros.com/articles/repair-lean-mixture-codes-p0171-or-p0174-on-some-manufacturers

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

The fact that it will not stay running until it warms up points to a vacuum leak as well as the PCM cannot adjust to the lean condition because it does not know that there is unmetered air coming into the engine.

Run through this material and let us know what turns up. Thanks
Jan 13, 2021 at 11:16 AM
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