Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Ambient Temperature Sensor Circuit (B1412/12)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Interior / Heating / Air Conditioning / Air Conditioning System / Ambient Temperature Sensor Circuit (B1412/12)

DESCRIPTION

The cooler (ambient temp. sensor) thermistor is installed in front of the cooler condenser assembly to detect the ambient temperature, which is used to control the air conditioning system. 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 cooler (ambient temp. sensor) thermistor changes in accordance with the ambient temperature. As the temperature decreases, the resistance increases. As the temperature increases, the resistance decreases.

The air conditioning amplifier assembly applies voltage (3.3 V) to the cooler (ambient temp. sensor) thermistor and reads voltage changes due to changes in the resistance of the cooler (ambient temp. sensor) thermistor.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

Memory

B1412/12

Ambient Temperature Sensor Circuit

Open or short in ambient temperature sensor circuit
  • Cooler (ambient temp. sensor) thermistor
  • Harness or connector between cooler (ambient temp. sensor) thermistor and air conditioning amplifier assembly
  • Air conditioning amplifier assembly

Memorized

(4 sec. or more)*
  • *: The air conditioning amplifier assembly stores this DTC if the malfunction has occurred for the period of time indicated in the brackets.

HINT:

If the ambient temperature is approximately -52.9°C (-63.22°F) or lower, DTC B1412/12 may be output even though the system is normal.

WIRING DIAGRAM

PROCEDURE

1.

READ VALUE USING TECHSTREAM

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Body Electrical / Air Conditioner / Data List.

(e) Read the Data List according to the display on the Techstream.

Body Electrical > Air Conditioner > Data List

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

Ambient Temp Sensor

Cooler (ambient temp. sensor) thermistor

Min.: -23.30°C (-9.94°F)

Max.: 65.95°C (150.71°F)

Actual ambient temperature displayed

-
Body Electrical > Air Conditioner > Data List

Tester Display

Ambient Temp Sensor

OK:

The display is as specified in the normal condition column.

OK

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

NG

2.

INSPECT COOLER (AMBIENT TEMP. SENSOR) THERMISTOR

(a) Remove the cooler (ambient temp. sensor) thermistor.

Click here

*a

Component without harness connected

(Cooler (Ambient Temp. Sensor) Thermistor)

*b

Sensing Portion

*c

Resistance (kΩ)

*d

Temperature (°C (°F))

*e

Allowable Range

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

1 - 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.

HINT:

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

NG

REPLACE COOLER (AMBIENT TEMP. SENSOR) THERMISTOR

OK

3.

CHECK HARNESS AND CONNECTOR (COOLER (AMBIENT TEMP. SENSOR) THERMISTOR - AIR CONDITIONING AMPLIFIER ASSEMBLY)

(a) Disconnect the J42 air conditioning amplifier assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J42-13 (TAM) - A3-2

Always

Below 1 Ω

J42-2 (SG-2) - A3-1

Always

Below 1 Ω

J42-13 (TAM) or A3-2 - Body ground

Always

10 kΩ or higher

J42-2 (SG-2) or A3-1 - Body ground

Always

10 kΩ or higher
OK

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
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