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Test Description

WARNING: This page is about a different car, the 2004 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.

The numbers below refer to the step numbers on the diagnostic table.

  1. 5:  Refer to Fuel System Diagnostics for a possible fuel condition if conditions were not corrected,
  2. 6:  If conditions were not corrected, a worn cam, worn intake, exhaust values or other engine mechanical failures may be at fault.
DTC P0171

Step Action Values Yes No
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
IMPORTANT: Refer to the DTCs that are set, other than P0171, before continuing.
  1. Install the scan tool.
  2. Start and idle the engine at normal operating temperature in the Closed Loop.
  3. Record the data for the Long Term fuel trim.
  4. Turn OFF the engine.
  5. Turn ON the ignition, with the engine OFF.
  6. Review the Freeze Frame/Failure Records, and record displayed data for this DTC.
Does the scan tool indicate that the Long Term fuel trim is greater than the specified value?		 23% Go to Step 3  Go to Diagnostic Aids
3
  1. Operate the engine at idle.
  2. Observe the HO2S parameters with a scan tool.
Does the scan tool indicate that the values are within the specified range and fluctuating?		 200-800 mV Go to Step 4  Go to Step 5 
4
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
Did you find and correct the condition?		 - Go to Step 7  Go to Step 6 
5  Turn OFF the engine.
  • Check the heated oxygen sensor (HO2S) for proper installation.
  • Check to ensure electrical connectors and wires are secured and not contacting the exhaust system.
  • Check for a short between the signal circuit and the low reference circuit.

Did you find and correct the condition?		 - Go to Step 7  Go to Fuel System Diagnosis
6  Operate the engine at idle.
  • Check for missing, loose, or leaking exhaust components, from the HO2S forward.
  • Check for vacuum leaks at the intake manifold, the throttle body, and the injector O-rings.
  • Check the air induction system and the air intake ducts for leaks.
  • Check the secondary air injection (AIR) system for leaks, incorrect air delivery, and shut off valve that is not closing.
  • Check the crankcase ventilation system for leaks. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.8L.

Did you find and correct the condition?		 - Go to Step 7  Go to Symptoms - Engine Mechanical in Engine Mechanical -3.8L
7
IMPORTANT: After repairs, use the Fuel Trim Reset function on the scan tool in order to reset the Long Term Fuel.
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running in the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 8 
8 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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