Toyota 4Runner: Ambient Temperature Sensor Circuit (B1412/12)

Toyota 4Runner Service Manual / Vehicle Interior / Heating / Air Conditioning / Air Conditioning System(for Automatic Air Conditioning System) / Ambient Temperature Sensor Circuit (B1412/12)

DESCRIPTION

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

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

DTC Code	DTC Detection Condition	Trouble Area
B1412/12	An open or short in the cooler thermistor (ambient temperature sensor) circuit.	Cooler thermistor (ambient temperature sensor) Harness or connector Air conditioning amplifier assembly

WIRING DIAGRAM

PROCEDURE

1.	READ VALUE USING TECHSTREAM (AMBIENT TEMPERATURE SENSOR)

(a) Use the Data List to check if the cooler thermistor (ambient temperature sensor) is functioning properly (See page ).

Air Conditioner

Tester Display	Measurement Item/Range	Normal Condition	Diagnostic Note
Ambient Temp Sensor	Cooler thermistor (ambient temperature sensor) / Min: -23.3°C (-9.94°F) Max: 65.95°C (150.71°F)	Actual ambient temperature displayed	Open in the circuit: -23.3°C (-9.94°F). Short in the circuit: 65.95°C (150.71°F).

Tester Display

Measurement Item/Range

Normal Condition

Diagnostic Note

Ambient Temp Sensor

Cooler thermistor (ambient temperature sensor) /

Min: -23.3°C (-9.94°F)

Max: 65.95°C (150.71°F)

Actual ambient temperature displayed

Open in the circuit: -23.3°C (-9.94°F).

Short in the circuit: 65.95°C (150.71°F).

OK:

The display is as specified in the normal condition column.

Result

Result	Proceed to
OK (When troubleshooting according to problem symptoms table)	A
OK (When troubleshooting according to the DTC)	B
NG	C

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

2.	INSPECT COOLER THERMISTOR (AMBIENT TEMPERATURE SENSOR)

(a) Remove the cooler thermistor (ambient temperature sensor) (See page ).

(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

Text in Illustration

*a	Sensing Portion
*b	Resistance
*c	Allowable Range
*d	Temperature

NOTICE:

Even slightly touching the sensor may change the resistance value. Be sure to hold the connector of the sensor.
When measuring, the sensor temperature must be the same as the ambient temperature.

HINT:

As the temperature increases, the resistance decreases (refer to the graph).

REPLACE COOLER THERMISTOR (AMBIENT TEMPERATURE SENSOR)

3.	CHECK HARNESS AND CONNECTOR (AMBIENT TEMPERATURE SENSOR - AIR CONDITIONING AMPLIFIER)

(a) Disconnect the A23 sensor connector.

(b) Disconnect the F42 amplifier connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
A23-1 - F42-5 (TAM)	Always	Below 1 Ω
A23-2 - F42-13 (SG-2)	Always	Below 1 Ω
F42-5 (TAM) - Body ground	Always	10 kΩ or higher
F42-13 (SG-2) - Body ground	Always	10 kΩ or higher

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY

REPAIR OR REPLACE HARNESS OR CONNECTOR

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