Factors Affecting Accuracy - OHC Temperature Display
The temperature display operates through the use of a thermometer sensor (15A022) mounted behind the front bumper/grille. The display can be changed from English to metric units.
The data from the temperature sensor must be processed and adjusted so that engine heat does not affect the displayed temperature. When the ignition is first turned on, the module checks to see if the ignition has been off for more than two hours. If it has, the currently sensed temperature is displayed. If the ignition has not been off for two hours and the sensed temperature is higher than it was when the vehicle was turned off, the old temperature will be displayed. If the ignition has not been off for two hours and the sensed temperature is lower than it was when the vehicle was turned off, the currently sensed temperature is displayed. To update the temperature, the module looks at several different factors, as listed below.
- If ignition has been on for less than five minutes, and was previously off for longer than two hours, the engine is cold and does not affect the temperature sensor. Therefore, the current sensor data is used.
Engine Warm, Updated Temperature Cooler
- If ignition has been on for longer than five minutes or if the ignition was off for less than two hours, the engine compartment may be warm from the heat of the engine. The current sensor data is used only if it is less than the stored temperature reading from before.
Engine Warm, Updated Temperature Warmer
- If the sensor data indicates a higher temperature, the module looks at the vehicle speed to determine whether engine heat is causing erroneous readings. A "high speed counter" is used to determine this. The counter is incremented when the speed is greater than 53 km/h (33 mph) and decremented when the speed is between 16-53 km/h (10-33 mph). If the speed is less than 16 km/h (10 mph), the counter is reset, and the displayed temperature is not updated from its last reading. If the counter is greater than two minutes, the currently sensed temperature is displayed. If the high-speed counter has counted less than two minutes, the temperature is allowed to increase only one degree per minute.
- If the temperature sensor is short- or open-circuited, the display will read SC or OC, respectively, instead of a temperature. If the temperature drops below 3.3°C (38°F) or is below 3.3° C (38°F) upon power-up, the display will alternate between displaying "ICE" and the temperature. The display will alternate every two seconds for a time of one minute.
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