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Home >> Chevrolet >> 2011 >> Volt >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls And Fuel - 1.4L (LUU) - DTC P0335 Through DTC P1255/P064A >> DTC P121B or P121C >> Circuit/System Testing

Circuit/System Testing

  1. Ignition OFF, disconnect the harness connector at the B75B mass air flow/intake air temperature sensor.
  2. Service Mode active, verify that a test lamp illuminates between the ignition voltage circuit terminal 4 and ground.
    • If the test lamp does not illuminate, test the ignition voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition voltage circuit fuse is open, test or replace the components on the ignition voltage circuit.
  3. Connect the test lamp between the control circuit terminal 2 and the ignition voltage circuit terminal 4.
  4. Service Mode active. Command the MAF Sensor Supply Voltage ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
    • If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K20 ECM.
    • If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 ECM.
  5. If all circuits test normal, test or replace the B75B mass air flow/intake air temperature sensor.
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