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HOMESERVICE MANUALSGMC2021TERRAIN SLT, 4WDREPAIR AND DIAGNOSISELECTRICALSTARTER12 V STARTING AND CHARGING - DIAGNOSTIC INFORMATION AND PROCEDURES (1 OF 2)DIAGNOSTIC INFORMATION AND PROCEDURESDTC P0621CIRCUIT/SYSTEM TESTING
2021 GMC Terrain SLT, 4WD

Circuit/System Testing

2021 GMC Terrain SLT, 4WDSECTION Circuit/System Testing
  1. Verify that a test lamp illuminates between the G13 Generator B+ circuit terminal A X1, A X2 (LYX), AX2 (LH7/LTG), B X1, X1 or 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.
    • Go to next step: If the test lamp illuminates 
  2. Ignition OFF, disconnect the X2 harness connector at the G13 Generator, engine running.
  3. Test for 1 V or greater between the control circuit terminal 1 X1 and ground.
    • If less than 1 V 
    1. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: 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 K20 Engine Control Module.
    • Go to next step: If 1 V or greater 
  4. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module, ignition ON.
  5. 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.

    • Go to next step: If 1 V or less 
  6. Test or replace the G13 Generator.
RENDER: 1.0x

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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.