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Home >> Chevrolet >> 2021 >> Blazer RS, FWD >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 9 (Engine Controls And Fuel - 2.5L (LCV) - Diagnostic Information And Procedures (1 Of 2)) >> Diagnostic Information and Procedures >> DTC P0171 or P0172 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different variant/trim than selected.
  1. Ignition - On / Vehicle - In Service Mode
  2. Verify the scan tool parameter: MAP Sensor = Altitude Versus Barometric Pressure - The value should be within the range listed in the table.
    • Go to next step: If in the specified range 
  3. Engine - Idling - At normal operating temperature
  4. Observe the scan tool parameter: Short Term Fuel Trim

    Disconnect the component: B75 Mass Air Flow Sensor

    Verify the scan tool parameter: Short Term Fuel Trim = Change is less than 20%

    • If the change is 20% or greater 

      Refer to: DTC P0101 

    • Go to next step: If the change is less than 20% 
  5. Connect the component: B75 Mass Air Flow Sensor
  6. Verify the scan tool parameter: Long Term Fuel Trim = -10 to 10%
    • If greater than 10% 
    1. Ignition/Vehicle - Off
    2. Verify the following conditions do not exist:
      • Air Cleaner Element - Missing
      • Evaporative Emission Canister - Cracked
      • Evaporative Emission Pipe - Leaking/Restricted
      • Exhaust System - Cracked/Leaking/Loose Clamps/Missing components/Restricted/Visible Damage - Refer to: Symptoms - Engine Exhaust
      • Fuel - Contaminated/Poor Quality - Refer to: Alcohol/Contaminants-in-Fuel Diagnosis
      • Fuel level - Low
      • Fuel Injectors - Malfunction/Restricted - Refer to: Fuel Injector Diagnosis
      • Fuel Pressure - Low - Refer to: Fuel System Diagnosis
      • Induction System/Intake Air Duct - Leaking
      • Intake Manifold/O-Ring - Fuel Injector/Throttle Body - Leaking
      • MAF Sensor - Contamination of the measuring element/Water intrusion
      • Positive Crankcase Ventilation System - Leaking/Restricted - Refer to: Crankcase Ventilation System Inspection/Diagnosis
      • Vacuum Hoses - Cracked/Leaking/Kinked/Loose Clamps/Missing components/Restricted
    • If less than -10% 
    1. Ignition/Vehicle - Off
    2. Verify the following conditions do not exist:
    • Go to next step: If between -10 and 10% 
  7. 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 data.

    Verify DTC P0171, P0172 is not set.

    • If the DTC sets 

      Repeat step 4

    • Go to next step: If no DTC is set 
  8. All OK.