Deck 28: Temperature Sensors

Question 1

The sensor that most determines fuel delivery when a fuelinjected engine is first started is the _____________.

A) O2S
B) ECT sensor
C) Engine MAP sensor
D) IAT sensor

Answer 1

A manifold absolute pressure sensor (MAP sensor) is particularly used in a fuel injection unit to detect the manifold pressure, which is further evaluated to determine fuel delivery for optimal combustion in an internal combustion engine of a vehicle.
On the other hand, oxygen sensors detect the exhaust gas concentration, whereas the internal air temperature (IAT) sensor is arranged at the intake manifold or mass airflow region to determine the temperature of the air entering the internal combustion engine of the vehicle. The engine coolant temperature sensor detects the temperature of the engine coolant for proper cooling and functioning of the engine.
Thus, the engine MAP sensor is considered to be suitable for determining the fuel delivery when a fuel-injected engine is first started.
Therefore, the correct option is
.

Question 2

How does a typical NTC temperature sensor work?

Answer 2

A temperature sensor circuit is shown in Figure 1:
Figure 1
A negative temperature coefficient (NTC) temperature sensor is designed as a thermistor formed by a semiconductor that works for a normal temperature range. A very little current flows through the applied ground when a sensor is in ideal non-used state.
The electrical conductivity of the temperature sensor increases with an increase in temperature, thus allows a portion of 5 V applied voltage to ground. This phenomenon results in a decrease in signal voltage that further indicates the operation of the temperature sensor.

Question 3

What happens to the voltage measured at the ECT sensor when the thermostat opens?

A) Increases slightly
B) Increases about 1 volt
C) Decreases slightly
D) Decreases about 1 volt

Answer 3

An engine coolant temperature (ECT) sensor is used to detect the temperature of the coolant in a vehicle. The sensor is actually a thermostat for reading the temperature changes. The resistance within the sensor increases when the temperature decreases, which further increases the applied voltage signal that is inputted to a powertrain control module (PCM).
Suppose a vehicle engine is in running operating condition. Here, the resistance within the sensor decreases when the temperature increases. In case the thermostat circuit opens the temperature starts decreasing with an increase in resistance. Increase in resistance will further increase the applied voltage. Thus, at an instant when the thermostat circuit opens the voltage will slightly increase.
Thus, the correct option is
.
A graph of the voltage readings with respect to temperature changes is represented in Figure 1:
Figure 1

Question 4

What is the difference between a stepped and a nonstepped ECT circuit?

Question 5

Two technicians are discussing a stepped ECT circuit. Technician A says that the sensor used for a stepped circuit is different than one used in a non-stepped circuit. Technician B says that a stepped ECT circuit uses different internal resistance inside the PCM. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 6

What temperature should be displayed on a scan tool if the ECT sensor is unplugged with the key on, engine off?

Question 7

When testing an ECT sensor on a vehicle, a digital multimeter can be used and the signal wires back probed. What setting should the technician use to test the sensor?

A) AC volts
B) DC volts
C) Ohms
D) Hz (hertz)

Question 8

What are the three ways that temperature sensors can be tested?

Question 9

When testing the ECT sensor with the connector disconnected, the technician should select what position on the DMM?

A) AC volts
B) DC volts
C) Ohms
D) Hz (hertz)

Question 10

If the transmission fluid temperature (TFT) sensor were to fail open (as if it were unplugged), what would the PCM do to the transmission shifting points?

Question 11

When checking the ECT sensor with a scan tool, about what temperature should be displayed if the connector is removed from the sensor with the key on, engine off?

A) 284°F (140°C)
B) 230°F (110°C)
C) 120°F (50°C)
D) -40°F (-40°C)

Question 12

Two technicians are discussing the IAT sensor. Technician A says that the IAT sensor is more important to the operation of the engine (higher authority) than the ECT sensor. Technician B says that the PCM will add fuel if the IAT indicates that the incoming air temperature is cold. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B

Question 13

A typical IAT or ECT sensor reads about 3,000 ohms when tested using a DMM. This resistance represents a temperature of about _____________.

A) -40°F (-40°C)
B) 70°F (20°C)
C) 120°F (50°C)
D) 284°F (140°C)

Question 14

If the transmission fluid temperature (TFT) sensor indicates cold automatic transmission fluid temperature, what would the PCM do to the shifts?

A) Normal shifts and normal operation of the torque converter clutch
B) Disable torque converter clutch; normal shift points
C) Delayed shift points and torque converter clutch disabled
D) Normal shifts but overdrive will be disabled

Question 15

A P0118 DTC is being discussed. Technician A says that the ECT sensor could be shorted internally. Technician B says that the signal wire could be open. Which technician is correct?

A) Technician A only
B) Technician B only
C) Both Technicians A and B
D) Neither Technician A nor B