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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 238 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.3L)DRIVE CYCLESINSPECTION/MAINTENANCE HEATED OXYGEN SENSOR HEATER SYSTEM SET PROCEDUREPROCEDURE
1999 GMC Forward Control 5.7 R, Automatic

Inspection/Maintenance Heated Oxygen Sensor Heater System Set Procedure: Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Procedure
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2003 GMC Sonoma, 2003 GMC Safari, 2003 GMC Jimmy, 2003 Chevrolet S10 Pickup, and 2003 Chevrolet Blazer. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Inspection/Maintenance (I/M) System Check? If yes, go to next step. If no, see INSPECTION/MAINTENANCE SYSTEM CHECK .
    2. NOTE: Whenever ignition is turned ON, ignition positive voltage is supplied to the HO2S heaters.
  2. After verifying the enable criteria, Turn ignition off for about 5 minutes to allow the sensors to cool before continuing with test. Preprogram scan tool with vehicle information before the ignition is turned ON. Ensure vehicle is within the Conditions for Running. See CONDITIONS FOR RUNNING . Set parking brake. Verify that the transmission is in Park (A/T) or Neutral (M/T). Turn OFF all of the accessories (e.g., A/C, blower fan, etc.). Start and allow engine to idle. Allow engine to idle for 2 minutes or until the I/M System Status indicator updates to YES. Did the HO2S Heater System Status update to YES? If yes, go to step  5. If no, go to next step.
  3. With a scan tool, observe the DTC Information. Does the scan tool indicate any failed DTCs? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
  4. To determine which DTCs are required to run in order to complete this test, see INSPECTION/MAINTENANCE SYSTEM DTCS  table. With a scan tool, observe the Not Ran Since Code Cleared display. Determine which of the DTCs required for a YES status has not run. Enter the DTC number in the Specific DTC menu of the scan tool. Operate the vehicle within the Conditions for Running. See CONDITIONS FOR RUNNING . Repeat the procedure until the scan tool indicates the diagnostic test has run. Repeat this procedure for any additional required DTCs that have not run. With a scan tool, observe the I/M System Status display. Did the HO2S Heater System Status update to YES? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. With a scan tool, observe the emission related DTC portion of the I/M System Status display. Does the scan tool indicate any Emission Related DTCs set? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.