Theory Of Operation

There are four Variable Valve Lift (VVL) Solenoids that control the operation of the Intake Rocker Arms for all six cylinders. Review the figure and table below for the VVL Solenoid locations and cylinder control:

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GENERAL OPERATION:  The VVL System is designed to vary the lift and duration of the Intake Valves, to maximize efficiency and engine torque, depending on engine operation. The VVL System consists of 2 step Intake Rocker Arms that are capable of operating in High Lift or Low Lift mode. The PCM energizes and de-energizes the four VVL Solenoids to control the engine oil pressure to the Rocker Arms, controlling low lift and high lift operation.

• To enter Low Lift Mode  the PCM provides 12.0 volts to the VVL Solenoid to energize the solenoid. When energized the VVL Solenoid opens allowing the supply oil pressure to pass through the solenoid to the control oil passage and Rocker Arm. The pressurized oil pushes against the springs in the lock pins forcing the pins to retract. This allows the center of the Rocker Arm to move down freely and operate in Low Lift Mode. It takes approximately 20.0 psi of engine oil pressure at the Rocker Arm to overcome the springs in the lock pins.
• To enter High Lift Mode  the PCM de-energizes the VVL Solenoid. The solenoid closes and the pressurized oil in the control passage passes through the VVL Solenoid to the exhaust passage. When the pressure is relieved the spring loaded lock pin extends keeping the center of the Rocker Arm in the High Lift position. The Rocker Arm defaults to High Lift mode when no oil pressure is present.

DIAGNOSTICS:  The PCM controls each VVL Solenoid with a High Side Driver (HSD) Circuit  . The PCM performs circuit diagnostics  on each VVL Solenoid HSD for an open or short in the circuitry.

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Typical High Side Driver and Fault Detection:  This type of driver circuit is generally used for relay control, controlling a solenoid or a similar type of driver device. The PCM provides 12 volts to operate the device when switched on. The PCM also provides fault detection for the device, wiring and internal driver. In the example below, the PCM uses an internal pull up diagnostic resistor and calibrated voltage reference (V-Ref) as a comparator for fault detection.

• Circuit Open and Circuit High Detection:  The PCM monitors for an open circuit  and short to voltage  when the internal driver is switched off. A small amount of amperage is provided to the device through the internal pull up diagnostic resistor  connected in series with the device. The diagnostic voltage is monitored between the pull up resistor and device, and compared to V-Ref. If the resistance in the device or circuitry becomes too large (approaches open) the voltage supply will increase on the comparator circuit  and become greater than V-Ref, and a fault is detected. A short to Battery voltage will have the same effect.
• Circuit Low Detection:  The PCM monitors for a short to ground  when the driver is turned on. When switched on, the voltage to the device should be close to the 12 volt supply voltage. A short to ground will pull the voltage at the comparator circuit  below V-Ref and a circuit low fault is detected.

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