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Home >> Buick >> 2004 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls (DTC P0140 To P0496) >> Engine Controls Diagnosis >> DTC P0172 >> Test Description

Test Description

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

  1. 5:  If the conditions were not corrected, refer to Fuel System Diagnosis for a possible fuel condition.
  2. 6:  An EVAP canister that is saturated will cause a rich condition. Fuel in the vacuum line to the fuel pressure regulator indicates a leaking regulator. If the 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 continuing.
  1. Install a scan tool.
  2. Start and idle the engine at the normal operating temperature in Closed Loop.
  3. Record the Long Term Fuel Trim data.
  4. Turn OFF the engine.
  5. Turn ON the ignition, with the engine OFF.
  6. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.
Does the scan tool indicate that the Long Term Fuel Trim is less than the specified value?		 -13% 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 conditions:
    • Blockage of the inlet screen of the MAF sensor
    • Splits or kinks in the vacuum hoses
    • Improper connections of the vacuum hoses-Refer to Emission Hose Routing Diagram .
    • Collapsed or restricted air intake duct
    • Dirty or restricted air filter
    • Objects blocking the throttle body
Did you find and correct the condition?		 - Go to Step 7  Go to Step 6 
5  Turn OFF the engine
  • Check the HO2S for proper installation.
  • Ensure that the electrical connectors and the wires are secure and not contacting the exhaust system.

Did you find and correct the condition?		 - Go to Step 7  Go to Fuel System Diagnosis
6  Inspect for the following conditions:
Did you find and correct the condition?		 - Go to Step 7  Go to Symptoms - Engine Mechanical in Engine Mechanical
7
IMPORTANT: After any of the above 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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