Theory Of Operation
When all conditions have been met for Multiple Displacement Solenoid (MDS) operation, each MDS is energized by the Powertrain Control Module (PCM) to transition the engine from 8 cylinder mode to 4 cylinder mode. By energizing the solenoid, oil pressure is supplied through a passageway in the Cylinder Head to the pair of lifters that coincide with each particular solenoid. The oil pressure pushes in the locking pins that allows the lifter to collapse, decoupling the valves and camshaft. It takes approximately 21.75 psi (1.5 bar) for the solenoids to operate properly. In order to maintain the oil pressure above the necessary amount, there is a boost oil pump that raises the supply oil to between approximately 43.5-50.74 psi (3-3.5 bar). The system has a mechanical pressure relief valve which will open above 87 psi (6 bar), preventing the pressure from increasing too high.
The oil passage that supplies oil to the boost oil pump for MDS system operation also provides the lubrication oil for the Turbocharger. There is a Turbocharger Oil Deactivation Solenoid in the lubrication circuit to the Turbocharger that is controlled by the Powertrain Control Module. When MDS operation is initiated, the Turbocharger Oil Deactivation Solenoid is energized, closing the flow of lubrication oil to Turbocharger. The PCM uses a Low Side Driver (LSD) to control the operation of the solenoid. The PCM performs electrical fault detection diagnostics on the control circuitry. The PCM monitors the oil pressure in the lubrication passage in order to determine if the solenoid is in the proper state when it is commanded on and off. See the figure below to help identify the components being diagnosed.
| NUMBER | COMPONENT | FUNCTION |
|---|---|---|
| 1 | Multiple Displacement Solenoid (MDS) 1 | Controls oil flow to the Intake Lifters for MDS operation on cylinders #2 and #3 |
| 2 | Multiple Displacement Solenoid (MDS) 2 | Controls oil flow to the Exhaust Lifters for MDS operation on cylinders #2 and #3 |
| 3 | Multiple Displacement Solenoid (MDS) 3 | Controls oil flow to the Exhaust Lifter for MDS operation on cylinder #1 |
| 4 | Multiple Displacement Solenoid (MDS) 4 | Controls oil flow to the Intake Lifter for MDS operation on cylinders #1 |
| 5 | Cylinder Deactivation Boost Pump | Increases the oil pressure for the MDS System operation |
| 6 | Turbocharger Oil Deactivation Solenoid | Controls flow of the lubrication oil to the Turbocharger |
| 7 | Oil Pressure Sensor 2 | Used to monitor oil pressure in the Turbocharger Oil Deactivation circuit |
| 8 | Oil Pressure Relief Valve | Regulates oil pressure for MDS System |
| 9 | Collapsible Lifters | Disengage the Valves during MDS mode |
| 10 | Oil Pressure Sensor 3 | Used to monitor oil pressure in the MDS circuit |
| 11 | MDS Oil delivery circuit | Oil supply to the Collapsible Lifters from the Boost Pump for MDS Operation |
| 12 | Oil input to Boost Pump | Oil supply to the Boost Pump for MDS operation |
| 13 | Oil lubrication circuit for Lifters | Normal oil flow to the Lifters |
Typical Low Side Driver Operation and Fault Detection: This type of driver circuit is generally used for relay control, solenoid control or a similar type of driver device. The PCM provides a ground to operate the device when switched on. The ground could be constant or Pulse Width Modulated (PWM). The PCM also provides fault detection for the device, wiring and internal driver. Fault detection can be done by monitoring voltage on the circuit, current draw, or a combination of both. For diagnostic purposes the PCM uses an internal pull down diagnostic resistor connected in series and a voltage reference (V-Ref) comparator for fault detection:
- Circuit Open and Circuit Low Detection: The PCM monitors for an open circuit and short to ground when the driver is switched off. When switched off, the available voltage passes through the device and the internal pull down resistor connected in series. The voltage at the comparator circuit should be close to Battery voltage since the majority of the voltage drop occurs through the diagnostic resistor. If the available voltage is less than the V-Ref, a fault is set. In this scenario the V-Ref would be slightly below Battery voltage. An alternative method of fault detection for an open or short to ground that is used is to monitor current draw when the internal driver is switched on. If the module does not detect any current draw it determines that the component or circuitry is open. Excessive current draw detected would indicate a short to ground.
- Circuit High Detection: The PCM monitors for a short to voltage when the driver is switched on. When the driver is switched on providing a path to ground through the transistor, the available voltage should be pulled low, near zero volts since the comparator circuit is monitoring the ground side of the device. If the voltage is greater than V-Ref, a fault is detected. In this scenario V-Ref would be slightly above zero volts.
A load that has a resistance that is below manufacturer specification, or a second load device shorted to the low side driver circuit can cause excessive current draw on the internal driver. The driver will be switched off to protect against overheating and damaging the driver. In this instance the Circuit High fault may be detected because the available voltage on the comparator circuit is above V-Ref.
