What is a VGT?
A Variable Geometry Turbocharger (VGT) is a turbocharger that is designed to allow the optimum air flow to be varied based on engine conditions. The optimum air flow or A/R (aspect ratio) varies depending on the engine speed (RPM) and engine load conditions. The A/R(aspect ratio) at low speeds is very different from the A/R(aspect ratio) at high speeds. Most variable geometry turbochargers (VGTs) are equipped with electronic actuator that use signals from the ECM to move the vanes or sliding sleeves in the VGT to increase or decrease the amount of exhaust gas to drive the turbine wheel, thereby increasing or decreasing the air intake flow to the turbocharger.
What Causes VGT Failure?
Variable geometry turbocharger (VGT) electronic actuator, while very effective at creating optimum power under varying engine conditions, can also cause problems when they failure. These actuators are electronically controlled, but they drive the turbine mechanically, which means they are subject to both mechanical and electronic failures.
In terms of mechanical failure, electronic actuator can be affected not only by wiring problems, but also by old-fashioned wear and tear. Problems with the turbocharger blades can also cause the electric actuator to failure. For example, if the turbocharger blades get stuck and cannot move the actuator, trying to rotate to move the blades open or closed may bind the actuator gear, causing the motor operating the gear to overheat and fail. it is very rare for a VGT Actuator gear to break, but it is possible.
In addition to mechanical failures, electronic failures can occur in the variable geometry turbocharger (VGT) electronic actuator. It is important to note that most electronically controlled VGT actuators are considered “smart devices,” meaning they communicate back and forth between the ECMs and send messages. These “smart devices” also have the ability to diagnose themselves, meaning that if the turbine blades get stuck and the gears do not reach the desired position, this information is transmitted to the ECM and in most cases a fault code is set and a warning light is activated to alert the operator of the problem. A typical VGT electronic actuator circuit will have a 12 volt power wire, loop or ground wire and 2 CAN bus or data link wires. a shorted ground on the 12 volt power wire could short out the actuator and cause a failure. If there is any problem with the CAN line, the ECM will not be able to send/receive information to/ from the actuator, therefore the ECM will not be able to properly control the position of the actuator, which in turn will cause performance problems.
Why Do I Need to Calibrated?
Most Variable Geometry Turbocharger (VGT) electronic actuator need to be calibrated after removal or replacement. The reason for calibrating these actuators is simply so that the actuator knows the range of motion to open and close the turbocharger blades or sliding sleeves in order to move the blades to the correct position when commanded by the ECM. Without calibration, the ECM and VGT electric actuators will not be able to position the vanes to optimize air flow into the engine and will cause performance problems and possibly premature failure of other components. For example, it is possible to generate too much boost at low engine speeds and too little boost at high engine speeds. This will result in high exhaust manifold pressures, affecting the air-fuel ratio and ultimately leading to low power problems.
VGT Troubleshooting Step
Troubleshooting a variable geometry turbocharger (VGT) requires separating the turbocharger assembly from the electric actuator to identify the problem, as VGT repairs can cost thousands of dollars, while replacing the electric actuator is much cheaper than buying a turbocharger. It is important to troubleshoot the VGT electric actuator while ensuring that the mechanical turbo components of the variable geometry turbocharger (VGT) are in order. The following is the troubleshooting process.
- The first step is to determine if there are any associated or related fault codes that may be causing the problem. If not, proceed to the next step.
- The next thing to verify is the battery voltage. Ideally, we would like to see 12.6 volts, but anything over 12 volts is enough to consider the voltage check passed and continue. 3.
- Once we are sure we have the proper voltage, the next step is to verify the voltage of the VGT electric actuator. Using a multimeter, check the voltage between the power supply pin or pin 1 and the return pin or pin 2 of the VGT actuator connector to see if the voltage is between 12 volts and 12.6 volts. When checking the voltage of the component, we are looking for a reading in the 1 volt battery voltage range, which means we are fully compliant with our specifications.
- Our next step is to determine any faults in the data link circuitry. In this case, if there is a problem with the circuit, there should be some associated faults and we need to correct these and recheck our faults.
- The final step before we determine the fault is to verify the termination resistance of the VGT actuator. Using a multimeter, check the resistance between pins 3 and 4 of the VGT electric actuator and find that the OL reading implies an open circuit. The resistance specification for the VGT actuator termination resistor is between 108 and 132 ohms. By reading the OL, it was determined that the specifications were met and that the VGT electric actuator was faulty. After determining that the VGT actuator is faulty, we need to replace and calibrate the new VGT actuator.