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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 104 (Engine Controls And Fuel - 6.0L (L96 LC8) - Diagnostic Information And Procedures (2 Of 2)) >> Diagnostic Information and Procedures >> DTC P1516, P2101, P2119, or P2176 >> 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. Ignition OFF.
    2. WARNING:

    Turn OFF the ignition before inserting fingers into the throttle bore. Unexpected movement of the throttle blade could cause personal injury.

  2. Verify the conditions listed below do not exist with the Q38 Throttle Body Assembly:
      NOTE:
      • The rest position is defined as the actual Throttle Position percentage when the ignition is OFF or with the ignition ON for greater than 30 seconds.
      • When the ignition is OFF, spring tension should hold the throttle plate in the rest position. You should be able to open the throttle plate to wide open throttle (WOT) or push the throttle plate to the fully closed position. In each case, the throttle plate should return to the rest position without assistance.
    • A throttle blade that is not in the rest position
    • A throttle blade that is binding open or closed
    • A throttle blade that is free to move open or closed without spring pressure
    • If a condition is found 

      Replace the Q38 Throttle Body.

    • Go to next step: If a condition is not found 
    3. NOTE:

    Disconnecting the throttle body harness connector may cause additional DTCs to set.

  3. Ignition OFF, disconnect the harness connector at the Q38 Throttle Body.
    4. NOTE:
    • Before testing each circuit, the ignition must be OFF and the ECM completely powered down.
    • The test lamp must be connected to the circuit before turning the ignition ON, or incorrect diagnosis may occur.
  4. Connect a test lamp between a motor control circuit listed below and ground.
    • TAC Motor Control Open circuit terminal 1
    • TAC Motor Control Closed circuit terminal 2
    5. NOTE:
    • The test lamp should illuminate then immediately turn OFF as the ignition is switched to the ON position.
    • Be prepared to observe the test lamp as the ignition is switched ON.
  5. Ignition ON, verify that a test lamp does not illuminate continuously after the ignition is switched to ON.
    • If the test lamp illuminates continuously 
    1. Ignition OFF, disconnect the appropriate harness connector at the K20 Engine Control Module and remove the test lamp, ignition ON.
    2. Test for less than 1 V between the control circuit and ground.
      • If 1 V or greater, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K20 Engine Control Module.
    • If the test lamp is always OFF 
    1. Ignition OFF, disconnect the appropriate harness connector at the K20 Engine Control Module and remove the test lamp.
    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 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • Go to next step: If the test lamp illuminates then turns OFF with ignition ON. 
  6. Ignition OFF, remove the test lamp. Set the DMM to the 40 V scale or higher, select the Min/Max Recording Mode, and set the Peak Min/Max response time to 1 ms or faster.
    7. NOTE:
    • The DMM Min/Max Recording Mode and the response time of 1 ms or faster must be reset after testing each circuit or a lower voltage will be recorded.
    • The ignition must be OFF and the ECM completely powered down before testing each circuit or a lower voltage will be recorded.
  7. Verify the Max voltage is within 3 V of B+, while using DMM Min/Max Recording Mode function on each control circuit listed below and ground, as the ignition is turned ON.
    • TAC Motor Control Open circuit terminal 1
    • TAC Motor Control Closed circuit terminal 2
    • If not within 3 V of B+ 
    1. Ignition OFF, disconnect the appropriate harness connector at the K20 Engine Control Module.
    2. Test for less than 2 Ω in the control circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • Go to next step: If within 3 V of B+ 
  8. Replace the Q38 Throttle Body.
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