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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1472 (Engine Control System - Diagnosis - 4.2L (DTC P0140 To DTC P0506)) >> Diagnosis >> DTC P0171 >> Test Description

Test Description

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

  1. 7:  If conditions were not corrected, a worn cam, worn intake or exhaust valves, 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: If any DTCs are set, except P0171, refer to those DTCs before proceeding with this diagnostic.
  1. Install a scan tool.
  2. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.
  3. Select Fuel Trim Data parameter.
  4. Start the engine and observe the Fuel Trim Index.
Does the scan tool indicate that the Fuel Trim Index is more than the specified value?		 20% Go to Step 3  Go to Diagnostic Aids
3
  1. Operate the engine at idle.
  2. Observe the O2S 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 8  Go to Step 7 
5
  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 pressure should be within the range specified for your altitude.
Does the MAP indicate the correct barometric pressure?		 - Go to Step 6  Go to DTC P0106
6
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    • The oxygen sensor (O2S) for proper installation
    • Ensure electrical connectors and wires are secured and not contacting the exhaust system.
    • A short between the signal circuit and low reference circuit
Did you find and correct the condition?		 - Go to Step 8  Go to Fuel System Diagnosis
7 
  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    • AIR shut-off valve is stuck open
    • Missing, loose, or leaking exhaust components
    • Vacuum leaks at the intake manifold, throttle body, and injector O-rings
    • The air induction system and air intake ducts for leaks
    • The crankcase ventilation system for leaks
Did you find and correct the condition?		 - Go to Step 8  Go to Symptoms - Engine Mechanical in Engine Mechanical
8
IMPORTANT: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  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 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 9 
9 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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