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Test Description

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

  1. 10:  If the conditions were not corrected, a worn CAM, a worn intake or exhaust valves or the engine mechanical failure 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 Are any DTCs other than DTC P0171 also set? - Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 3 
3
  1. Install the scan tool.
  2. Turn ON the ignition.
  3. Observe the Freeze Frame/Failure Records parameter with a scan tool and record the displayed data for this DTC.
  4. Start and idle the engine at normal operating temperature in the Closed Loop.
  5. Observe the Long Term FT parameter.
Does the scan tool indicate that the Long Term fuel trim is more than the specified value?		 18.8% Go to Step 4  Go to Diagnostic Aids
4
  1. Operate the engine at idle.
  2. Observe the heated oxygen sensor (HO2S) 1 sensor parameter with a scan tool.
Does the scan tool indicate that the HO2S 1 voltage is within the specified range and fluctuating?		 200-800 mV Go to Step 5  Go to Step 6 
5
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
Did you find and correct the condition?		 - Go to Step 11  Go to Step 10 
6
  1. Turn OFF the engine.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the manifold absolute pressure (MAP) sensor pressure parameter with a scan tool. Refer to Altitude vs Barometric Pressure .
  4. The MAP sensor parameter should be within the range specified for your altitude.
Does the MAP indicate the correct barometric pressure?		 - Go to Step 7  Go to Manifold Absolute Pressure (MAP) Sensor Diagnosis
7
  1. Turn OFF the engine.
  2. Inspect both HO2S for proper installation. Refer to Heated Oxygen Sensor Replacement - Position 1 and Heated Oxygen Sensor Replacement - Position 2 .
  3. Ensure that the electrical connectors and wires are secured and not contacting the exhaust system.
Did you find and correct the condition?		 - Go to Step 11  Go to Step 8 
8 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 11  Go to Step 9 
9 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 11  Go to Fuel System Diagnosis
10 
  1. Operate the engine at idle.
  2. Inspect for the following conditions:
Did you find and correct the condition?		 - Go to Step 11  Go to Symptoms - Engine Mechanical
11
IMPORTANT: Reset the Long Term Fuel Trim with the scan tool Fuel Trim Reset function after any of the above repairs.
  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 12 
12 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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