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HOMESERVICE MANUALSCHEVROLET2009TAHOE BASE, 4.8 CREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 394 (BATTERY, CHARGING SYSTEM AND STARTING SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0621CIRCUIT/SYSTEM TESTING
2009 Chevrolet Tahoe Base, 4.8 C

Circuit/System Testing

2009 Chevrolet Tahoe Base, 4.8 CSECTION Circuit/System Testing
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2011 GMC Yukon XL, 2011 GMC Yukon, 2011 Chevrolet Tahoe, 2011 Chevrolet Suburban, and 2011 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
  1. Verify that a test lamp illuminates between the G13 generator B+ terminal 1 X2 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition OFF.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition OFF.
    2. Test for greater than 100 Ω between the B+ circuit and ground.
      • If 100 Ω or less, repair the short to ground on the circuit.
      • If greater than 100 Ω, replace the generator.
    • If the test lamp illuminates 
  2. Ignition OFF, disconnect the X1 harness connector at the generator, ignition ON.
  3. Test for 4.5-5.5 V between the control circuit terminal 1 X1 and ground.
    • If less than 4.5 V 
    1. Ignition OFF, disconnect the harness connectors at the ECM.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If greater the 2 Ω, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the ECM.
    • If greater the 5.5 V 
    1. Ignition OFF, disconnect the harness connectors at the ECM, ignition ON.
    2. Test for less than 1 V between the control circuit and ground.
      • If greater than 1 V, repair the short to voltage on the circuit.
      • If less than 1 V, replace the ECM.
    • If between 4.5-5.5 V 
  4. Test or replace the generator.
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