Component Testing

2020 Chevrolet Express 2500 LS, 2.8L Eng VIN 1SECTION Component Testing

M74 Window Motor - Test

  1. Ignition/Vehicle & All vehicle systems - Off
  2. Disconnect the appropriate electrical connector:M74 Window Motor
  3. Connect a 25 A fused jumper wire between the test points: Control terminal 1 & B+
  4. Momentarily connect a jumper wire between the test points: Control terminal 2 & Ground

    Reverse the jumper wires 2 times between the terminals.

    Verify the component works as specified: M74 Window Motor = Up & Down

    • If not the specified state 

      Replace the component:M74 Window Motor

    • Go to next step: If the specified state 
  5. All OK.

S79P Window Switch - Passenger - Test

  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: S79P Window Switch - Passenger
  3. Test for infinite resistance between the test points:
    • Ignition terminal A & Control terminal D - Switch - Not Pressed
    • Ignition terminal A & Control terminal H - Switch - Not Pressed
    • If less than infinite resistance 

      Replace the component: S79P Window Switch - Passenger

    • Go to next step: If infinite resistance 
  4. Test for less than 3 ohms between the test points:
    • Control terminal D & Control terminal F - Switch - Not Pressed
    • Control terminal H & Control terminal G - Switch - Not Pressed
    • If 3 ohms or greater 

      Replace the component: S79P Window Switch - Passenger

    • Go to next step: If less than 3 ohms 
  5. Operate the component: S79P Window Switch - Passenger - Pressed & Pulled
  6. Test for less than 3 ohms between the test points:
    • Ignition terminal A & Control terminal F
    • Ignition terminal A & Control terminal G
    • If 3 ohms or greater 

      Replace the component: S79P Window Switch - Passenger

    • Go to next step: If less than 3 ohms 
  7. All OK.

S79D Window Switch - Driver - Test

  1. Ignition/Vehicle - Off
  2. Disconnect the electrical connector: S79D Window Switch - Driver
  3. Test for infinite resistance between the test points:
    • Ignition terminal C & Control terminal A - Switch - Not Pressed
    • Ignition terminal C & Control terminal D - Switch - Not Pressed
    • Ignition terminal C & Control terminal G - Switch - Not Pressed
    • Ignition terminal C & Control terminal H - Switch - Not Pressed
    • If less than infinite resistance 

      Replace the component: S79D Window Switch - Driver

    • Go to next step: If infinite resistance 
  4. Test for less than 3 ohms between the test points:
    • Ground terminal F & Control terminal A - Switch - Not Pressed
    • Ground terminal F & Control terminal D - Switch - Not Pressed
    • Ground terminal F & Control terminal G - Switch - Not Pressed
    • Ground terminal F & Control terminal H - Switch - Not Pressed
    • If 3 ohms or greater 

      Replace the component: S79D Window Switch - Driver

    • Go to next step: If less than 3 ohms 
  5. Operate the component: S79D Window Switch - Driver - Pressed & Pulled
  6. Test for less than 3 ohms between the test points:
    • Ignition terminal C & Control terminal G
    • Ignition terminal C & Control terminal H
    • If 3 ohms or greater 

      Replace the component: S79D Window Switch - Driver

    • Go to next step: If less than 3 ohms 
  7. Operate the component:Passenger Window Switch @ S79D Window Switch - Driver - Pressed & Pulled
  8. Test for less than 3 ohms between the test points:
    • Ignition terminal C & Control terminal A
    • Ignition terminal C & Control terminal D
    • If 3 ohms or greater 

      Replace the component: S79D Window Switch - Driver

    • Go to next step: If less than 3 ohms 
  9. All OK.
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

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.