Oil Viscosity Sensor - Operation

OPERATION

The viscosity sensor is used by the engine management system to help determine the operational strategy of the variable valve actuation. However, in ambient conditions above -25°C (-13°F) the viscosity signal is not used by the engine management system.

When the oil temperature is between -25°C (-13°F) and -35°C (-31°F), the engine management system will use the signal from the viscosity sensor to determine the oil viscosity level. If the engine management system determines that the oil viscosity is too low (thick oil), the glow plug light on the instrument panel will flash and a text message appears on the EVIC telling the driver to warm the engine.

During extreme cold starts, colder than -35°C (-31°F), the engine management system will prevent the engine from starting. In this extreme cold condition, the glow plug light on the instrument panel will flash and a text message appears on the EVIC telling the operator to warm the engine.

The viscosity sensor measures the viscosity of the oil with a tuning fork shaped sensor that uses vibration to measure the viscosity. The tuning fork is vibrated at a set frequency for a determined amount of time. When the vibration from the sensor is turned off, the vibration of the sensor that is caused by the surrounding fluid is monitored. The frequency and rate of change of the vibrations reflects the viscosity of the fluid.

There are multiple components contained within the viscosity sensor. In the sensing end (immersed in the oil) is the tuning fork sensor and a thermocouple sensor. These sensors are attached to an integrated circuit (IC) board in the body of the sensor which monitors the sensors. There are two more IC's in the sensor that provide power management and an output from the viscosity sensor.

The viscosity output from the sensor is provided to the PCM as a hardwired input. The output is a pulse width modulated (PWM) signal that the PCM will recognize and translate into a viscosity value. The viscosity sensor can also provide a temperature output as a PWM signal but at this time, the temperature signal is not used.