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Home >> Buick >> 2005 >> Park Avenue Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System (DTC P0140 To DTC P0442) >> Diagnosis >> DTC P0171 >> Test Description

Test Description

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. 8:  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 - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
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 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 9  Go to Step 8 
5 
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    • The heated oxygen sensor (HO2S) for proper installation
    • Ensure electrical connectors and wires are secured and not contacting the exhaust system
    • For a short between the signal circuit and the low reference circuit

      Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?		 - Go to Step 9  Go to Step 6 
6 Test the HO2S 1 low signal circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 9  Go to Step 7 
7 Test for a short between the signal circuit and the low reference circuit or ground. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 9  Go to Fuel System Diagnosis
8 
  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    • For missing, loose, or leaking exhaust components, from the HO2S forward
    • For vacuum leaks at the intake manifold, the throttle body, and the injector O-rings
    • The air induction system and the air intake ducts for leaks
    • The secondary air injection (AIR) system, if equipped, for leaks, incorrect air delivery, and a shut off valve that is not closing
    • The crankcase ventilation system for leaks-Refer to Crankcase Ventilation System Inspection/Diagnosis .
Did you find and correct the condition?		 - Go to Step 9  Go to Symptoms - Engine Mechanical
9
IMPORTANT: After repairs, use the Fuel Trim Reset function on the scan tool to reset the long term fuel.
  1. Turn ON the ignition, with the engine OFF.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. 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 10 
10 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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