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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1042 (Engine Controls Diagnosis - 4.8L, 5.3L, & 6.0L (DTCS P0141 To P0446)) >> Diagnosis >> DTC P0171 or P0174 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. 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 Diagnosis for a possible fuel problem.
  2. 6:  If conditions were not corrected, a worn cam, worn intake or exhaust valves, or other engine mechanical failure may be the problem.
DTC P0171 or P0174

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 other than P0171 or P0174 are set, 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.
  4. Turn OFF the engine.
  5. Turn ON ignition, with 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 greater than the specified value?		 23% Go to Step 3  Go to Diagnostic Aids
3
  1. Operate engine at idle.
  2. Observe the HO2S parameters with a scan tool.
Does the scan tool indicate that the parameter is 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 7  Go to Step 6 
5 
  1. Turn OFF the engine.
  2. Inspect the heated oxygen sensor (HO2S) for proper installation.
  3. Verify the electrical connectors and the wires are secure, and not contacting the exhaust system.
  4. Test for continuity between the HO2S 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 
  1. Operate the engine at idle.
  2. Inspect for any missing, loose, or leaking exhaust components forward of the HO2S.
  3. Inspect for vacuum leaks at the intake manifold, throttle body, and injector O-rings.
  4. Inspect the air induction system and the air intake ducts for leaks.
  5. Inspect the secondary air injection (AIR) system for leaks, improper air delivery, and for the shut-off valves not closing.
  6. Inspect the crankcase ventilation system for leaks. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 4.8L, 5.3L, and 6.0L.
Did you find and correct the condition?		 - Go to Step 7  Go to Symptoms - Engine Mechanical in Engine Mechanical - 4.8L, 5.3L, and 6.0L
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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