LEMON Manuals: Even more car manuals for everyone
Home >> Buick >> 2004 >> Century Limited >> Repair and Diagnosis >> External Pages >> Different car >> Section 89 (Engine Controls Diagnosis 3.8L (DTC P0138 To P0453)) >> Diagnosis >> DTC P0172 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 Buick Regal. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 5:  If conditions were not corrected, refer to Fuel System Diagnostic for possible fuel problem.
  1. 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 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 the 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 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. Start and operate the engine at idle.
  2. Observe 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:
    • Inlet screen of the mass air flow (MAF) sensor for blockage
    • Vacuum hoses for splits, kinks, and proper connections-Refer toEmission Hose Routing Diagram .
    • The air intake duct for being collapsed or restricted
    • The air filter for being dirty or restricted
    • Check 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. Visually and physically inspect the following items:
    • The heated oxygen sensor (HO2S) for proper installation
    • The electrical connectors and wires are secured and not contacting the exhaust system
  3. 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:
Did you find and correct the condition?		 - Go to Step 7  Go to Fuel System Diagnosis
7
IMPORTANT: After repairs, use 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 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 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
scientia non olet · About LEMON Manuals