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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 P0172 >> Test Description

Test Description

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

  1. 6:  An evaporative emission (EVAP) canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a bad regulator. If conditions were not corrected, a worn cam, worn intake or exhaust valves or other engine mechanical failure may be at fault.
DTC P0172

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 other than P0172, refer to those DTCs before proceeding with this diagnostic.
  1. Install a scan tool.
  2. Review the Freeze Frame/Failure Records and record displayed data for this DTC.
  3. Select Fuel Trim Data parameter.
  4. Start the engine and observe the Fuel Trim Index.
Is the Fuel Trim Index parameter less than the specified value?		 -35% Go to Step 3  Go to Diagnostic Aids
3
  1. Start and operate the engine at idle.
  2. Observe 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:
    • Vacuum hoses for splits, kinks, and proper connections-Refer to Emission Hose Routing Diagram .
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • For objects blocking throttle body
Did you find and correct the condition?		 - Go to Step 7  Go to Step 6 
5
  1. Turn OFF the engine.
  2. Inspect the oxygen sensor (O2S) for proper installation.
  3. Ensure electrical connectors and wires are secured and not contacting the exhaust system.
  4. Test for continuity between the signal circuit and the low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 7  Go to Fuel System Diagnosis
6  Inspect for the following:
  • Excessive fuel in the crankcase
  • The evaporative emissions (EVAP) control system
  • The fuel pressure regulator for proper operation-Refer to Fuel System Diagnosis .
  • Ensure that all injectors are functioning properly. Refer to Fuel Injector Coil Test .

Did you find and correct the condition?		 - Go to Step 7  Go to Symptoms - Engine Mechanical in Engine Mechanical
7
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 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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