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Home › Chevrolet › 2024 › Express 2500 LS, 6.6L Eng VIN 7 › Repair and Diagnosis › Engine Performance › System › Data Communications › Diagnostic Information and Procedures › DTC U1346 › Circuit/System Testing

Circuit/System Testing

NOTE:

Use the schematics and connector end views to identify the following:

  • The master control module and the LIN devices on the same LIN serial data circuit
  • The master control module's LIN serial data circuit terminal and the LIN device's B+, ignition, ground, and LIN serial data circuit terminals
  1. Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. Disconnect the harness connectors at the B75C Multifunction Intake Air Sensor. It may take up to 10 min for all vehicle systems to power down.
  2. Test for less than 10 Ω between the ground circuit terminal 4 and ground.
    • If 10 Ω or greater 
    1. Ignition/Vehicle OFF.
    2. Test for less than 2 Ω in the ground circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, repair the open/high resistance in the ground connection.
    • Go to next step: If less than 10 Ω 
  3. Ignition ON/Vehicle In Service Mode.
  4. Verify a test lamp illuminates between the ignition circuit terminal 1 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for less than 2 Ω in the ignition 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 OK and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Ignition/Vehicle OFF, remove the test lamp.
    2. Test for infinite resistance between the ignition circuit and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • If infinite resistance, replace the B75C Multifunction Intake Air Sensor.
    • Go to next step: If the test lamp illuminates 
    5. NOTE:

    For accurate voltage reading, disconnect the battery charger prior to performing the following test step.

  5. Test for 3.5-12 V between the LIN serial data circuit terminal 3 and ground.
    • If less than 3.5 V 
    1. Ignition/Vehicle OFF, disconnect the harness connectors at the K20 Engine Control Module.
    2. Test for infinite resistance between the LIN serial data circuit terminal and ground.
      • If less than infinite resistance, repair the short to ground in the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the LIN serial data circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • Go to next step: If less than 2 Ω
    4. Replace the K20 Engine Control Module.
    • If greater than 12 V 
    1. Ignition/Vehicle OFF, disconnect the harness connectors at the K20 Engine Control Module.
    2. Ignition ON/Vehicle In Service Mode.
    3. Test for less than 1 V between the LIN serial data circuit terminal and ground.
      • If 1 V or greater, repair the short to voltage in the circuit.
      • Go to next step: If less than 1 V
    4. Replace the K20 Engine Control Module.
    • Go to next step: If between 3.5-12 V 
  6. Ignition/Vehicle OFF, inspect both harness and component connectors for contamination, corrosion, and terminal tension.
  7. Reconnect the harness connectors at the B75C Multifunction Intake Air Sensor. Verify all connectors/terminals are fully seated.
  8. Ignition ON/Vehicle In Service Mode.
  9. Verify the DTC is not set again.
    • If the DTC is set 

      Replace the B75C Multifunction Intake Air Sensor.

    • Go to next step: If the DTC is not set 
  10. A fault is currently not present and may be an intermittent condition.
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