Throttle position (TP) sensor

Throttle position (TP) sensor

The TP sensor measures the angle of throttle opening and the rate of change of throttle position. The angle of throttle opening gives an indication of the quantity of air being drawn into the engine. The rate of change of throttle angle gives an indication of rate of acceleration demanded.

The sensor is a rotary variable resistor mounted to the throttle butterfly spindle giving an output of 0 to 5 volts.

Engine coolant temperature (ECT) sensor

The coolant temperature sensor measures the temperature of the engine coolant. The signal from the coolant sensor is used by the ECM to adjust the fuelling mixture. The engine requires a richer mixture at lower temperatures.

The sensor relies on a temperature dependent resistive metal strip. The resistance of the metal strip varies considerably with temperature and is immersed in the engine coolant.

If the sensor fails, the ECM assumes an engine coolant figure of 80°C. The fault could be noticable during the engine warm up period.

Fuel temperature sensor

The fuel temperature sensor measures the temperature of the fuel rail. The signal from the sensor gives the ECM a warning of fuel vapourisation and the possibility of bubbles forming in the injectors. If the ECM receives a high fuel temperature signal during starting, the fuel injector opening period is increased to clear any vapourisation bubbles from the injectors and correct the fuelling. When the engine is running, fuel circulation from the fuel tank keeps the fuel rail cool and flushes away any bubbles.