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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 94 (Engine Controls And Fuel - 2.8L (LWN) Diesel - Diagnostic Information And Procedures (3 Of 3)) >> Diagnostic Information and Procedures >> DTC P21CB >> 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, disconnect the X1 harness connector at the K115 Reductant Control Module. Ignition ON.
  2. Verify that a test lamp illuminates between the module ignition voltage circuit terminal 5 and ground.
    • If the test lamp does not illuminate 
    1. Ignition Off, remove the test lamp and remove fuse F40 from the X50A Underhood Fuse Block.
    2. Test for less than 2Ω in the module ignition voltage 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
    3. Test for infinite resistance between the module ignition voltage circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    • Go to next step: If the test lamp illuminates 
  3. Ignition ON, verify that a test lamp illuminates between the module ignition voltage circuit terminal 8 and ground.
    • If the test lamp does not illuminate 
    1. Ignition Off, remove the test lamp and remove the KR121A Reductant Control Module Relay 1 from the X50A Underhood Fuse Block.
    2. Test for less than 2Ω in the module ignition voltage 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
    3. Test for infinite resistance between the sensor ignition voltage circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    • Go to next step: If the test lamp illuminates 
  4. Replace the K115 Reductant Control Module.
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