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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 15 (Battery, Starting System And Charging System) >> Diagnostic Information and Procedures >> Starter Malfunction >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
  1. Verify a test lamp turns On between the test points: B+ circuit terminal 1 or A@M64 Starter Motor & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 ohms between the test points: B+ circuit terminal 1 or A@M64 Starter Motor & Output terminal@Fuse
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points: B+ circuit terminal 1 or A@M64 Starter Motor & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Replace the component: M64 Starter Motor
    • Go to next step: If the test lamp turns On 
    2. NOTE:

    It may take up to 2 min for all vehicle systems to power down before an accurate ground or low reference circuit continuity test can be performed.

  2. Ignition/Vehicle & All vehicle systems - Off
  3. Remove the component: KR27 Starter Relay
  4. Test for less than 10 ohms between the test points: Ground circuit terminal 86 & Ground
    • If 10 ohms or greater 
    1. Disconnect the ground connection: Ground Connection@The other end of the circuit
    2. Test for less than 2 ohms between the test points: Ground circuit terminal 86 & Ground terminal@The other end of the circuit
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 ohms 
  5. Connect a test lamp between the test points: Control circuit terminal 85 & Ground circuit terminal 86
  6. Ignition - On / Vehicle - In Service Mode
  7. Perform the appropriate scan tool control function:
    • {If available}Starter Motor Relay - On and Off
    • {If available}Starter Relay - On and Off

      Verify the test lamp turns On and Off.

    • If the test lamp is always Off 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector: K20 Engine Control Module
    3. Test for infinite resistance between the test points: Control circuit terminal 85@Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    4. Test for less than 2 ohms between the test points: Control circuit terminal 85@Relay Socket & The other end of the circuit@Control module harness
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Replace the component: K20 Engine Control Module
    • If the test lamp is always On 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Disconnect the electrical connector: K20 Engine Control Module
    3. Ignition - On / Vehicle - In Service Mode
    4. Test for less than 1 V between the test points: Control circuit terminal 85@Relay Socket & Ground
      • If 1 V or greater - Repair the short to voltage on the circuit.
      • If less than 1 V - Replace the component: K20 Engine Control Module
    • Go to next step: If the test lamp turns On and Off 
  8. Verify a test lamp turns On between the test points: B+ circuit terminal 30 & Ground
    • If the test lamp does not turn On and the circuit fuse is OK 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for less than 2 ohms between the test points: B+ circuit terminal 30@Relay Socket & Output terminal@Fuse
      • If 2 ohms or greater - Repair the open/high resistance in the circuit.
      • If less than 2 ohms - Verify the fuse is OK and there is voltage at the fuse.
    • If the test lamp does not turn On and the circuit fuse is open 
    1. Ignition/Vehicle - Off & Remove - Test lamp
    2. Test for infinite resistance between the test points: B+ circuit terminal 30 & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Disconnect the electrical connector: X1@M64 Starter Motor
    4. Test for infinite resistance between the test points: Control circuit terminal 87@Relay Socket & Ground
      • If less than infinite resistance - Repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    5. Replace the component: M64 Starter Motor
    • Go to next step: If the test lamp turns On 
  9. Momentarily connect a 40 A fused jumper wire between the test points: B+ circuit terminal 30 & Control circuit terminal 87

    Verify the component does not turn On and Off when connecting and disconnecting the jumper wire: M64 Starter Motor

    • If the component turns On and Off 

      Test or replace the component: KR27 Starter Relay

    • Go to next step: If the component does not turn On and Off 
  10. Ignition/Vehicle & All vehicle systems - Off
  11. Install the component: KR27 Starter Relay
  12. Disconnect the electrical connector: X1@M64 Starter Motor
  13. Connect a test lamp between the test points: Control circuit terminal 1 or A & Ground
  14. Ignition - On / Vehicle - In Service Mode
  15. Perform the appropriate scan tool control function:
    • {If available}Starter Motor Relay - On and Off
    • {If available}Starter Relay - On and Off

      Verify the test lamp turns On and Off.

    • If the test lamp is always Off 

      Repair the open/high resistance in the circuit: Control Circuit

    • If the test lamp is always On 

      Repair the short to voltage on the circuit: Control Circuit

    • Go to next step: If the test lamp turns On and Off 
  16. Test or replace the component: M64 Starter Motor
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