Electrical Sensors
Whats the difference between sensors and sending units?
Sensors provide information to electronic control units and sending units provide information to instrument guages.
5 resistive sensors?
Rheostats, potentiometers, thermistors, piezoresistive and wheatstone bridge pressure sensors.
Difference between active and passive sensors?
Active sensors use a current supplied by the ecm to operate while passive sensors do not.
5 voltage generators?
Oxygen, NOx, ammonia, variable reluctance and piezoelectric sensors.
What is reference voltage and its typical voltage?
Regulated voltage supplied by the ecm to sensors. Typically 5 volts.
What is a pull-up switch?
A switch connected between the ecm and battery positive. Circuit inside the module will measure voltage drop across a fixed resistor inside ECM.
What is a pull-down switch?
Switch connected between ECM and negative ground. When the switch is closed, ground current will flow into the ecm and voltage drop is measured.
What are resistive sensors?
Three wire pressure, temperature and position sensors. Class of sensors that will change a voltage signal applied to the sensor.
What are thermistors?
Temperature sensitive variable resistors used to measure coolant, oil, fuel and air temperatures. They provide analog data, two types are NTC and PTC. NTC are most common.
What are Rheostats?
Two wire variable resistance sensors, used to signal sending units such as fuel and oil pressure. They use a variable sliding contact along a resistive wire. Current intensity will vary depending on the position.
Purpose of the reference voltage wire? (Three-wire)
Carries voltage to sensor by ECM. If its an active sensor, Vref will supply current to operate an integrated chip inside device.
What does "IVS" stand for?
Idle validation switch. A safety system part of the throttle position sensor in case there is uncontrolled acceleration of the engine. At idle one switch will be open and the other will be closed, and off idle the switches change state. At idle, the state of the switch must correspond to the TPS voltage sensed by the ECM. Idle = Low vref signal return from TPS/5 vref return through IVS return, throttle active will be open. (Pg 565 truck).
What is the purpose of the ground wire? (Three wire sensor).
Provides a negative ground signal through the ECM and not to engine ground. This ground is also called zero bolt return (ZVR). It is free of any type of electrical interference. In resistive sensors, the ZVR acts as a reference point to measure voltage drop across the sensor.
What is the purpose of the signal wire? (Three wire sensor).
Provides a positive voltage proportional to the physical value measured by the sensor.