Circuit DescriptionThe variable geometry turbocharger (VGT) is electronically activated by the VGT actuator. The VGT actuator is a smart device and receives information via the J1939 data link from the primary engine control module (ECM). The VGT actuator performs its own diagnostics and reports malfunctions back to the primary engine ECM, using the J1939 data link. The ECM then decodes the error message and converts it to a fault code.

The exhaust gas recirculation (EGR) valve is controlled by a brushless motor located on top of the EGR valve. The EGR valve motor uses three different motor legs to move the valve through its range of motion. The ECM uses the EGR motor A, B, and C wires to command the EGR valve to the appropriate position in order to meet EGR flow targets.The EGR valve motor contains three position sensors that detect the location of the EGR valve. These sensors report the position of the valve back to the ECM over the EGR valve position A, B, and C wires.

Component LocationThe VGT actuator is located on the turbocharger bearing housing.

The EGR Valve and EGR Differential Pressure Sensor location varies depending on engine model.

Conditions for Running the DiagnosticsThis diagnostic runs continuously when the engine is running.

Conditions for Setting the Fault CodesThe Engine Control Module (ECM) detected the EGR flow, intake manifold pressure, or exhaust pressure was unable to meet the command.

Action Taken When the Fault Code is ActiveThe ECM illuminates the amber CHECK ENGINE lamp and/or Malfunction Indicator Lamp (MIL) after the diagnostic fails on two consecutive trips.

Conditions for Clearing the Fault CodeTo validate the repair, it may be necessary to operate the vehicle on a chassis dynamometer or to drive the vehicle in order to get the engine load high enough for the diagnostic to run.

Shop TalkTroubleshoot any fault codes related to the intake manifold pressure/temperature, EGR differential pressure, barometric pressure, exhaust gas pressure, VGT, EGR, or engine intake air throttle prior to troubleshooting 4612.

Possible Cause:1) Charge-air cooler failure2) ECM calibration