Outside Air Temperature Display
The outside air temperature display system consists of an ambient sensor, CUSTOM CPU, and liquid crystal display installed in the combination meter. The ambient sensor is located on the radiator stay behind the front grille for efficient exposure to the outside air. It detects the outside air temperature by using a built-in thermistor, which varies its resistance according to changes in the ambient temperature, then sends the signal to the CUSTOM CPU. The thermistor can only detect an average temperature of the outside air and cannot respond to sharp changes in the temperature because its exterior is made of a plastic to increase the thermal capacity. See Fig 1 . As soon as the ignition switch is turned ON, the CUSTOM CPU will compare the temperature data that was sent from the ambient sensor to the temperature data stored in its memory from the time that the ignition switch was turned OFF. The CUSTOM CPU displays the lower temperature. However, if 60 minutes or more has elapsed between the last ignition switch turn OFF and the next turn ON, then the displayed temperature is a sensor-provided temperature. See Fig 2 and Fig 3 . The indicator can give a false reading under any of the following conditions:
- When there is too much sun
- While idling, running at low speeds in a traffic jam, or when the engine is immediately restarted after a shutdown
- When the actual outside temperature falls beyond the specified indicator range (-22° to 122°F / -30° to 50°C)
When the vehicles running slowly, the heat released from the engine compartment will raise the air temperature around the ambient sensor, which affects the temperature data sent to the CUSTOM CPU. The CPU then calculates the outside temperature by using vehicle speed data. For example, when the vehicle is running at a speed slower than 10 km/h, the CPU will use the temperature that was last detected during speeds exceeding 10 km/h rather than using the temperature being currently provided by the ambient sensor.