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Home >> Cadillac >> 2021 >> CT4 Sport, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 135 (12 V Starting And Charging - Diagnostic Information And Procedures) >> Diagnostic Information and Procedures >> Starter Malfunction (Except LF4) >> Circuit/System Testing

Circuit/System Testing

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Starter Drive Test

  1. Ignition OFF and all vehicle systems off, disconnect the KR27C Engine Restart Relay.
  2. Verify a test lamp illuminates between ground circuit terminal 86 and B+.
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on circuit 6450 or ground connection.
    • Go to next step: If the test lamp illuminates 
  3. Ignition on, connect a test lamp between the control circuit terminal 85 and ground.
  4. Verify the test lamp turns ON and OFF while commanding the Starter Drive ON and OFF with the scan tool.
    • If the test lamp is always OFF 
    1. Test circuit 4325 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Test circuit 4325 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found
    3. Replace the K20 Engine Control Module.
    • If the test lamp is always ON 
    1. Test circuit 4325 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found
    2. Replace the K20 Engine Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  5. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate and the fuse is good. 

      Replace the X50A Fuse Block - Underhood

    • If the test lamp does not illuminate and the fuse is open 
    1. Test circuit 4358 for a short to ground
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the M64 Starter Motor.
    • Go to next step: If the test lamp illuminates. 
  6. Ensure the parking brake is applied and the automatic transmission is in PARK or manual transmission is in NEUTRAL. Momentarily install a 40 A fused jumper between terminal 30 and terminal 87.
  7. Verify the Starter Drive clicks.
    • If the Starter Drive clicks 

      Replace the KR27C Engine Restart Relay

    • Go to next step: If the Starter Drive does not click. 
  8. Replace the M64 Starter.

Starter Motor Test

  1. Verify a test lamp illuminates between the B+ terminal A X2 at the M64 Starter and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Test the B+ circuit 442 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open or high resistance is not found
    2. Verify the fuse is good and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Test the B+ circuit 442 a short to ground
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the M64 Starter.
    • Go to next step: If the test lamp illuminates 
  2. Ignition OFF and all vehicle systems off, disconnect the KR27 Starter Relay.
  3. Verify a test lamp illuminates between ground circuit terminal 86 and B+.
    • If the test lamp does not illuminate 
    1. Repair the open/high resistance on circuit 6450 or ground connection.
    • Go to next step: If the test lamp illuminates 
  4. Ignition on, connect a test lamp between the control circuit terminal 85 and ground.
  5. Verify the test lamp turns ON and OFF while commanding the Starter Motor ON and OFF with the scan tool.
    • If the test lamp is always OFF 
    1. Test circuit 625 for a short to ground.
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Test circuit 625 for an open/high resistance.
      • If an open/high resistance is found, repair the fault on the circuit.
      • Go to next step: If an open/high resistance is not found
    3. Replace the K20 Engine Control Module.
    • If the test lamp is always ON 
    1. Test circuit 625 for a short to voltage.
      • If a short to voltage is found, repair the fault on the circuit.
      • Go to next step: If a short to voltage is not found
    2. Replace the K20 Engine Control Module.
    • Go to next step: If the test lamp turns ON and OFF 
  6. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
    • If the test lamp does not illuminate and the fuse is good. 

      Replace the X50A Fuse Block - Underhood.

    • If the test lamp does not illuminate and the fuse is open 
    1. Test circuit 6 for a short to ground
      • If a short to ground is found, repair the fault on the circuit.
      • Go to next step: If a short to ground is not found
    2. Replace the M64 Starter.
    • Go to next step: If the test lamp illuminates. 
  7. Ensure the parking brake is applied and the automatic transmission is in PARK or manual transmission in NEUTRAL. Momentarily install a 30 A fused jumper between terminal 30 and terminal 87.
  8. Verify the M64 Starter Motor Spins.
    • If the starter spins 

      Replace the KR27 Starter Relay

    • Go to next step: If the starter does not spin 
  9. Replace the M64 Starter.
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