Page 222 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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206 Automobile mechanical and electrical systems

Figure 2.257 Coolant thermistor

Figure 2.259 Construction of a zirconia type lambda sensor

The engine coolant temperature sensor is an NTC thermistor ( Fig. 2.257 ). It is of
a similar type to the air temperature sensor. It is fi tted into the water jacket close
to the thermostat or bypass coolant circuit passages. The sensor measures the
engine coolant temperature and provides a signal voltage to the ECU. This is
Figure 2.258 Exhaust gas oxygen used for cold-start and warm-up enrichment as well as fast idle speed control
(lambda) sensor
through the idle speed control valve.
The Greek letter (λ) lambda is used as the symbol for a chemically correct air to
fuel ratio; hence the use of this letter for naming the sensor that is used to control
Key fact the amount of fuel delivered, so that a very close tolerance to the stoichiometric
ratio is maintained. The lambda sensor is often known as an EGO sensor ( Figs
The engine coolant temperature 2.258 and 2.259 ). Some of these sensors are electrically heated. Preheating
sensor is a negative temperature
coeffi cient (NTC) thermistor. allows the sensor to be fi tted lower down in the exhaust stream and prolongs the
life of the active element. The sensor measures the presence of oxygen in the
exhaust gas and sends a voltage signal to the engine ECU.
More fuel is delivered when oxygen content is detected and less fuel when it

is not. In this way, an accurate fuel mixture close to the stoichiometric ratio is
maintained. This produces the correct exhaust gas constituents for chemical
reactions in the catalytic converter. Exhaust gases pass over the active element
Key fact
and when the oxygen concentration on each side is different an electric voltage
The lambda sensor is often known is produced. Voltages of about 0.8 V for little or no exhaust oxygen and 0.2 V for
as an exhaust gas oxygen sensor.
higher content are typical outputs.
The sensors for power steering and air conditioning are pressure or mechanically
operated switches. They provide a voltage signal when the system is in
operation. The ECU uses these signals to increase the engine idle speed to
accept the increased engine load.
Switches are used in automatic transmission. They include the neutral
drive switch, which is used for idle speed control, the kick-down switch for
acceleration control, and the brake on/off switch, which is used to ensure that
the torque converter lock-up clutch is released. This is to prevent the engine
stalling as the vehicle comes to rest.
A sensor can be used to measure exhaust gas pressure ( Fig. 2.260 ). It uses a
ceramic resistance transducer, which responds to the exhaust gas pressure
applied through a pipe connection to the exhaust system. The signal voltage
from the electronic pressure transducer is used to regulate the EGR valve. The
valve may be operated directly from the ECU if electromechanical or by vacuum
through a solenoid vacuum switch.