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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 P0172 >> 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:  A plugged air filter can cause a rich condition and set a DTC P0172.
  3. 4:  Engine control sensors that are found to be out range (skewed) or fixed, can cause the engine to run rich. 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 circuits for resistance. High circuit resistance can cause the sensor to read the incorrect volume of air, resulting in the wrong fueling condition. Refer to the applicable sensor DTC table for direction in diagnosing any possible sensor error.
DTC P0172

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 more than the specified value?		 -20% Go to Diagnostic Aids Go to Step 3 
3  Visually and physically check the air filter and the air induction assembly for any of the following conditions:
  • A dirty or contaminated air filter
  • Any restrictions or blockage of the air flow
  • Any leaks in the exhaust system

Did any of the above inspections isolate a condition requiring a repair?		 - Go to Step 9  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 pre-catalyst heated oxygen sensor (HO2S 1)
  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 any errant readings for their cause and repair as necessary.
Was a repair necessary?		 - Go to Step 9  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 a 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
  1. Check the evaporative emission (EVAP) control system for possible over-purging of the EVAP system. Refer to Evaporative Emission (EVAP) Control System Diagnosis .
  2. Repair as necessary.
Was a problem found?		 - Go to Step 9  Go to Step 7 
7
  1. Remove and visually and physically inspect the HO2S 1 for silicon contamination. Contamination will be indicated by a powdery white deposit on the portion of the HO2S that is exposed to the exhaust stream.
  2. If contamination is evident on the HO2S, replace the contaminated sensor and correct the source of contamination. Refer to Heated Oxygen Sensor Replacement - Position 1 .
Did the sensor require replacement?		 - Go to Step 9  Go to Step 8 
8 Is a rich condition still present? - Go to Symptoms - Engine Controls Go to Step 9 
9
  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 10  Go to Step 2 
10 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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