Toyota Avalon (XX50) 2019-2022 Service & Repair Manual: Ambient Temperature Display System

DESCRIPTION

The thermistor assembly is installed in front of the cooler condenser assembly to detect the ambient temperature, which is used to control the automatic air conditioning system. The thermistor assembly detects fluctuations in the ambient temperature and sends it as a signal to the combination meter assembly. This data is used for controlling the cabin temperature. The resistance of the thermistor assembly changes in accordance with the ambient temperature. As the temperature decreases, the resistance increases. As the temperature increases, the resistance decreases. The combination meter assembly applies voltage (5 V) to the thermistor assembly and detects voltage changes due to changes in the resistance of the thermistor assembly.

NOTICE:

The thermistor assembly detects the ambient temperature in its vicinity, not the ambient temperature around the vehicle. Depending on factors such as radiant heat from the engine room and the vehicle speed, the ambient temperature detected by the thermistor assembly may differ from the ambient temperature displayed on the multi-information display in the combination meter assembly. For example:

• When the vehicle is stopped or being driven at low speeds, the displayed ambient temperature will not be updated to a higher temperature to adjust for and minimize the influence of radiant heat from the engine room on the automatic air conditioning system control. When the vehicle is not being driven at low speeds, the adjustment is performed, but updating of the displayed ambient temperature to a higher temperature is delayed. The displayed ambient temperature will be updated to a lower temperature regardless of the vehicle speed.
• When the ambient temperature around the thermistor assembly suddenly changes due to any reason other than radiant heat from the engine room, such as when the vehicle enters or exits a garage or tunnel, the actual ambient temperature of the vehicle and the displayed ambient temperature may differ or changing of the displayed value may be delayed.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

• Before performing an inspection, move the vehicle to an area where all of the following conditions are met:
  • The ambient temperature changes little.
  • The ground temperature is low.
  • There are no heat sources, such as a stove, another vehicle with its engine running or an exhaust duct, near.
• Perform the following procedure with the engine switch on (IG). Do not start the engine.

PROCEDURE

(a) Check for DTCs.

B

GO TO DTC B1412

A

(a) Remove the thermistor assembly.

Click here

(b) Inspect the thermistor assembly.

Click here

NG

REPLACE THERMISTOR ASSEMBLY

OK

(a) Disconnect the G36 air conditioning amplifier assembly connector.

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

Standard Resistance:

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

(a) Disconnect the cable from the negative (-) battery terminal and wait for at least 90 seconds.

NOTICE:

After turning the engine switch off, waiting time may be required before disconnecting the cable from the negative (-) battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) battery terminal notices before proceeding with work.

Click here

HINT:

The air conditioning amplifier assembly stores the value of the last ambient temperature detected by the thermistor assembly before the engine switch was turned off for up to 1 hour after the engine switch is turned off. It is necessary to clear this value.

(b) Connect the cable to the negative (-) battery terminal.

(c) Measure and make a note of the ambient temperature near the thermistor assembly using a thermometer.

NOTICE:

• Perform the following procedure with the engine switch on (IG).
• Wait at least 6 minutes for the values of the thermistor assembly and thermometer to become stable before taking a measurement.
• Hold the thermometer 50 mm (1.97 in.) from the thermistor assembly with its sensing portion at the same height and perpendicular to the thermistor assembly.
• Hold the sensor only by its connector. Touching the sensing portion may change the resistance value.
• When measuring the ambient temperature with a thermometer, do not move the thermometer, touch the sensing portion or allow it to contact the vehicle body.

(d) Make a note of the ambient temperature displayed on the multi-information display in the combination meter assembly.

(e) Compare the value of the ambient temperature measured by the thermometer and the thermistor assembly.

OK:

The value of the ambient temperature measured by the thermometer and the thermistor assembly are almost the same.

OK

END

NG

REPLACE AIR CONDITIONING AMPLIFIER ASSEMBLY