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Home >> Isuzu >> 2007 >> Ascender 4WD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System & Fuel System - 4.2L - DTC P0135 To DTC P0420 >> DTC P0171 >> Test Description

Test Description

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

  1. 8:  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 - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2
IMPORTANT: Disregard any transmission symptoms, antilock brake system (ABS) indicators and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.
Are any DTCs other than P0171 also set?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 3 
3
  1. Install a scan tool.
  2. Review the Freeze Frame/Failure Records and record the displayed data for this DTC.
  3. Select the Fuel and Emission data list.
  4. Start the engine.
  5. Observe the Long Term FT parameter with a scan tool.
Is the Long Term FT parameter more than the specified value?		 19% Go to Step 4  Go to Diagnostic Aids 
4
  1. Operate the engine at idle.
  2. Observe the heated oxygen sensor (HO2S) parameters with a scan tool.
Does the scan tool indicate that the HO2S parameters are within the specified range and fluctuating?		 200-800 mV Go to Step 5  Go to Step 6 
5
  1. Turn OFF the engine.
  2. Visually and physically inspect the following items:
Did you find and correct the condition?		 - Go to Step 9  Go to Step 8 
6
  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.
  4. The MAP sensor pressure should be within the range specified for your altitude. Refer to Altitude Versus Barometric Pressure .
Do the MAP parameters indicate the correct barometric pressure?		 - Go to Step 7  Go to DTC P0106
7
  1. Turn OFF the engine.
  2. Inspect for the following conditions:
    • Proper HO2S installation
    • Electrical connectors and wires are secured and not contacting the exhaust system
    • An open or a short to ground in the HO2S signal circuit
Did you find and correct the condition?		 - Go to Step 9  Go to Fuel System Diagnosis
8 
  1. Operate the engine at idle.
  2. Inspect for the following conditions:
    • Secondary air injection (AIR) shut-off valve stuck open
    • Missing, loose or leaking exhaust components
    • Vacuum leaks at the intake manifold, throttle body and injector O-rings
    • Leaks at the air intake ducts
    • Leaking crankcase ventilation system
Did you find and correct the condition?		 - Go to Step 9  Go to Symptoms - Engine Mechanical
9
IMPORTANT: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  1. Turn ON the ignition, with the engine OFF.
    2. IMPORTANT: DO NOT clear codes with the engine running. The codes may reset in the same ignition cycle.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. 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 10 
10 To verify that the performance of the catalytic converter has not been affected by the condition that set this DTC, perform the Repair Verification for DTC P0420. Refer to DTC P0420 .
Did you complete the procedure?		 - Go to Step 11  Go to DTC P0420 
11 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle System OK
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