Lexus NX manuals

Lexus NX: Ambient Temperature Display System

Lexus NX Service Manual / Vehicle Interior / Heating / Air Conditioning / Air Conditioning System / Ambient Temperature Display System

DESCRIPTION

The thermistor assembly (ambient temperature sensor) is installed in front of the cooler condenser assembly to detect the ambient temperature which is used to control the air conditioning system AUTO mode. This sensor is connected to the air conditioning amplifier assembly and detects fluctuations in the ambient temperature. This data is used for controlling the cabin temperature. The sensor sends a signal to the air conditioning amplifier assembly. The resistance of the thermistor assembly (ambient temperature sensor) changes in accordance with the ambient temperature. As the temperature decreases, the resistance increases. Conversely, as the temperature increases, the resistance decreases.

The air conditioning amplifier assembly applies a voltage (5 V) to the thermistor assembly (ambient temperature sensor) and reads voltage changes due to changes in the resistance of the thermistor assembly (ambient temperature sensor).

NOTICE:

The thermistor assembly (ambient temperature sensor) is installed on the front of the cooler condenser assembly in the engine room and detects the ambient temperature around the installation area (the ambient temperature detected is the temperature detected around the thermistor assembly (ambient temperature sensor) and not the ambient temperature of the air surrounding the vehicle). Therefore, the ambient temperature around the thermistor assembly (ambient temperature sensor) changes depending on the radiated heat from the engine room and the ambient temperature display value is affected by vehicle speed. In the following cases, the ambient temperature of the air surrounding the vehicle and the displayed value are different and the speed at which the displayed value updates is delayed. However, this is not a malfunction.

  • When the vehicle is stopped or being driven at a low speed, the value is not updated to a higher temperature in order to minimize the effects of the radiated heat from the engine on the heater and air conditioner "AUTO" control. Since the same adjustment also occurs while the vehicle is being driven at medium to high speeds, updating to a higher temperature is delayed. However, the value is updated to a lower temperature regardless of the vehicle speed.
  • The ambient temperature around the thermistor assembly (ambient temperature sensor) installation area drastically changes due to a cause other than the radiated heat from the engine (vehicle garage, entering or exiting a tunnel, etc.).

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • After the power switch is turned off, there may be a waiting time before disconnecting the negative (-) auxiliary battery terminal.

    Click here

  • When disconnecting and reconnecting the auxiliary battery terminal

    Click here

    HINT:

    When disconnecting and reconnecting the auxiliary battery, there is an automatic learning function that completes learning when the respective system is used.

    Click here

  • Before starting the inspection, it is necessary to release the residual heat from the engine room (engine unit and coolant hoses, etc.) after stopping the engine and electric motor (when the vehicle is parked after being driven). Therefore, move and park the vehicle in the following type of temperature measurement location.
    • A location within the vehicle service area which has a relatively low amount of environmental temperature changes in the area surrounding the vehicle.
    • A location with a level surface made of a material such as concrete which transmits a relatively low amount of heat from the ground, such as concrete.
    • A location with no heat influences around the vehicle to be inspected such as other vehicles with a running engine and electric motors, exhaust gas ducts installed on the exhaust pipes, stoves, etc.
  • When the auxiliary battery terminal is disconnected or the air conditioning amplifier assembly is replaced, be sure to perform servo motor initialization.

    Click here

  • The air conditioning system uses the CAN communication system. Inspect the communication function by following How to Proceed with Troubleshooting. Troubleshoot the air conditioning system after confirming that the communication system is functioning properly.

    Click here

  • Power switch operation during parked vehicle inspection:

    Turn the power switch on (IG). (Do not start the engine and electric motor.)

PROCEDURE

1.

CHECK FOR DTC

(a) Clear the DTC.

Click here

Body Electrical > Air Conditioner > Clear DTCs

(b) Check for DTCs when the following conditions are met.

Click here

Body Electrical > Air Conditioner > Trouble Codes

NOTICE:

During the parked vehicle inspection, perform the inspection with the power switch on (IG) (do not start the engine and electric motor).

Result

Proceed to

DTC B1412 is not output

A

DTC B1412 is output

B
B

GO TO DTC B1412

A

2.

INSPECT THERMISTOR ASSEMBLY (AMBIENT TEMPERATURE SENSOR)

NOTICE:

During the parked vehicle inspection, perform the inspection with the power switch off (do not start the engine and electric motor).

(a) Disconnect the thermistor assembly (ambient temperature sensor) connector.

(b) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

A16-1 - A16-2

10°C (50°F)

3.00 to 3.73 kΩ

15°C (59°F)

2.45 to 2.88 kΩ

20°C (68°F)

1.95 to 2.30 kΩ

25°C (77°F)

1.60 to 1.80 kΩ

30°C (86°F)

1.28 to 1.47 kΩ

35°C (95°F)

1.00 to 1.22 kΩ

40°C (104°F)

0.80 to 1.00 kΩ

45°C (113°F)

0.65 to 0.85 kΩ

50°C (122°F)

0.50 to 0.70 kΩ

55°C (131°F)

0.44 to 0.60 kΩ

60°C (140°F)

0.36 to 0.50 kΩ

NOTICE:

  • Hold the sensor only by its connector. Touching the sensing portion may change the resistance value.
  • When measuring, the sensor temperature must be the same as the ambient temperature.
  • Use a thermometer to detect the ambient temperature of the installation area around the thermistor assembly (ambient temperature sensor).

HINT:

As the temperature increases, the resistance decreases (see the graph).

*a

Component without harness connected

(Thermistor Assembly (Ambient Temperature Sensor))

*b

Sensing Portion

*c

Resistance (kΩ)

*d

Temperature (°C (°F))

*e

Allowable Range
NG

REPLACE THERMISTOR ASSEMBLY (AMBIENT TEMPERATURE SENSOR)

OK

3.

CHECK HARNESS AND CONNECTOR (THERMISTOR ASSEMBLY [AMBIENT TEMPERATURE SENSOR] - AIR CONDITIONING AMPLIFIER ASSEMBLY)

NOTICE:

During the parked vehicle inspection, perform the inspection with the power switch off (do not start the engine and electric motor).

(a) Disconnect the A16 thermistor assembly (ambient temperature sensor) connector.

(b) Disconnect the I50 air conditioning amplifier assembly connector.

(c) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

A16-2 - I50-5 (TAM)

Always

Below 1 Ω

A16-1 - I50-13 (SG-2)

Always

Below 1 Ω

A16-2 - A16-1

Always

10 kΩ or higher

A16-2 or I50-5 (TAM) - Body ground

Always

10 kΩ or higher

A16-1 or I50-13 (SG-2) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

CHECK AMBIENT TEMPERATURE COMPARISON

(a) Disconnect the cable from the negative (-) auxiliary battery terminal.

NOTICE:

Make sure the wire harness(es) and connector(s) for the vehicle being inspected are connected. After the power switch is turned off, the navigation system stores the various memory and settings within approximately 6 minutes. Therefore, make sure to disconnect the cable from the negative (-) auxiliary battery terminal after confirming that 6 minutes or more have elapsed since turning the power switch off.

(b) Disconnect the cable from the negative (-) auxiliary battery terminal and wait 90 seconds or more.

HINT:

The air conditioning amplifier assembly reads and memorizes the thermistor assembly (ambient temperature sensor) detection value (THO) from before the power switch was turned off for 1 hour after turning the power switch off. Therefore, it is necessary to switch off the air conditioning amplifier assembly internal power source and clear the stored values from before the power switch was turned off.

(c) Connect the cable to the negative (-) auxiliary battery terminal.

(d) Using a thermometer, measure the ambient temperature of the installation area around the thermistor assembly (ambient temperature sensor) and record it.

NOTICE:

  • During the parked vehicle inspection, perform the inspection with the power switch on (IG) (do not start the engine and electric motor).
  • Set the thermometer so that the measuring tip is at approximately the same height and lateral position as the thermistor assembly (ambient temperature sensor) installed behind the front grille and approximately 5 cm from the surface of the front grille, and then maintain the thermometer in that position.
  • After the power switch is turned on (IG), the ambient temperature, detected signal value and sensing portion temperature of the thermistor assembly (ambient temperature sensor) and the measuring tip of the thermometer will equalize. Therefore, make sure to wait approximately 6 minutes before measuring.
  • If the temperature sensing portion of the thermistor assembly (ambient temperature sensor) is touched, the body temperature of the technician may cause an incorrect temperature measurement. Therefore, do not touch the temperature sensor when measuring the ambient temperature of the installation area around the thermistor assembly (ambient temperature sensor).
  • Do not move the thermometer from the maintained position, touch the measuring tip or allow it to contact the front grille.

(e) Record the ambient temperature value displayed on the multi-information display of the combination meter assembly.

(f) Compare the ambient temperature of the installation area around the thermistor assembly (ambient temperature sensor) with the ambient temperature value displayed on the multi-information display of the combination meter assembly.

Standard:

The ambient temperature of the installation area around the thermistor assembly (ambient temperature sensor) is approximately the same as the ambient temperature value displayed on the multi-information display of the combination meter assembly.

OK

END
NG

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

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