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2003 5.3 suburban P0171 and P0174

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Jan 17, 2016, 11:13 AM

Post #1 of 3 (958 views)
2003 5.3 suburban P0171 and P0174 Sign In

Changed both upstream sensors. Bank one sensor fluctuates much lower milivolts than Bank two sensor. Seems to run too good for vacum leak.

Hammer Time
Ultimate Carjunky / Moderator
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Jan 17, 2016, 11:47 AM

Post #2 of 3 (951 views)
Re: 2003 5.3 suburban P0171 and P0174 Sign In

Seems to run too good for vacum leak.

I don't know where you get that idea. Those codes simply mean that the computer has reached it's adaptive limit in it's attempt to maintain 14.7:1 air/fuel ratio.

Vacuum leaks or intake snorkel leak are the #1 causes of thise codes. The 0/2s are the very least likely causes, especially when it's both banks.

You need to have the engine smoke tested.


We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.

(This post was edited by Hammer Time on Jan 17, 2016, 11:48 AM)

Tom Greenleaf
Ultimate Carjunky / Moderator
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Jan 17, 2016, 11:49 AM

Post #3 of 3 (948 views)
Re: 2003 5.3 suburban P0171 and P0174 Sign In

Just because those codes come up doesn't mean toss the O2 sensors as you've found out - common mistake.
Fault Code Definition
  • OBD II P0171 Fuel System Too Lean (Bank 1)
  • OBD II P0174 Fuel System Too Lean (Bank 2)

  • Check Engine Light will illuminate
  • In some cases, no adverse conditions may be noticed by the driver
  • In other cases, there may be performance problems, such as a lack of power on acceleration and some "coughing" or misfiring
  • The vehicle may have trouble idling, especially when warm or when sitting at a stoplight

Common Problems That Trigger the P0171 and P0174 Code
  • PCM software needs to be updated
  • Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
  • Mass Airflow Sensor (MAF)
  • Plugged Fuel Filter or weak Fuel Pump
  • Plugged or dirty Fuel Injectors

Common Misdiagnosis
  • Oxygen Sensors

Polluting Gases Expelled
Now you can check the more common reasons and add checking fuel pressure to the things listed above not always the fuel pump either,


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