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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1383 (Engine Control System Diagnosis (DTC P0130 To DTC P0456) -- 1.8L (LNK)) >> Diagnosis >> DTC P0171 >> Test Description

Test Description

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

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

  1. 1:  The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 3:  Visually and physically checking items that may cause a lean condition that may determine the reason that the DTC set.
  3. 4:  Engine control sensors that are found to be out range (skewed) or fixed, can cause the engine to run lean. Inspect the performance of the MAF sensor. Inspect for air restrictions and air inlet leaks near the MAF sensor. If the HO2S voltage is fixed low, while the fuel trim is constantly high, check the MAF sensor signal circuit for resistance. High circuit resistance can cause the sensor to read a lower volume of air than actual, resulting in a lean fueling condition. Refer to the applicable sensor DTC table for direction in diagnosing any possible sensor error.
  4. 6:  Contaminants in the fuel, such as alcohol or water, can create a lean condition and set DTC P0171. Small amounts of water delivered to the fuel injectors and cause a lean exhaust indication. A lean exhaust indication can also be caused by too much alcohol in the fuel.
DTC P0171

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1  Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2
  1. Start the engine.
  2. Operate the vehicle until the loop status indicates Closed Loop.
  3. Observe the Short Term FT parameter display on the scan tool.
Is the Short Term FT parameter displayed on the scan tool less than the specified value?		 20% Go to Diagnostic Aids Go to Step 3 
3  Visually and physically check for any of the following conditions:
  • Splits, kinks, and improper connections in the vacuum hoses
  • Correct installation of the PCV valve
  • Leaks in the exhaust system

Did any of the above inspections isolate a condition requiring a repair?		 - Go to Step 10  Go to Step 4 
4 
  1. Start the engine.
  2. Run the engine until the engine reaches a normal operating temperature.
  3. Observe the operation of the following sensors at idle, with a scan tool.
    • The mass air flow (MAF) sensor
    • The engine coolant temperature (ECT) sensor
    • The throttle position (TP) sensor
  4. Compare the observed sensor readings with the Typical Scan Tool Data Values located in the engine scan tool data list. Refer to Scan Tool Data List .
  5. Inspect the vehicle for the cause of any errant sensor readings and repair as necessary.
Was a repair necessary?		 - Go to Step 10  Go to Step 5 
5
  1. Turn OFF the ignition.
  2. Install a fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal .
  3. Observe the fuel pressure with the engine running at normal operating temperature.
Is the fuel pressure within the specified range?		 301-347 kPa (44-50 psi) Go to Step 6  Go to Fuel System Diagnosis
6  Check the fuel for excessive water, alcohol, or other contaminants. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Was the fuel contaminated?		 - Go to Step 7  Go to Step 8 
7 Replace the contaminated fuel.
Is the action complete?		 - Go to Step 10  -
8
  1. Perform the Fuel Injector Balance Test. Refer to Fuel Injector Balance Test with Special Tool .
  2. Repair or replace as necessary.
Was a repair necessary?		 - Go to Step 10  Go to Step 9 
9 Is a lean condition still present? - Go to Symptoms - Engine Controls Go to Step 10 
10
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?		 - Go to Step 11  Go to Step 2 
11 With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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