General Description
Temperature - Resistance Chart For Sensors:
The engine coolant temperature sensor is mounted in a coolant passage located in the cylinder head. The engine coolant temperature sensor is a thermistor-type sensor. A thermistor resists the flow of electricity similar to a resistor. However, the resistance of a thermistor increases as the temperature drops. For example, at a low air temperature a thermistor produces a high resistance of 93k ohms at -40°C (-40°F), while a high temperature causes low resistance of 65 ohms at 140°C (248°F).
The engine coolant temperature sensor is a two-wire sensor that receives a reference signal voltage from the PCM to sensor pin A and a sensor reference ground from the PCM to sensor pin B.
The PCM supplies the 5-volt reference signal to the engine coolant temperature sensor through a current-limiting resistor located inside the PCM. The signal received by the PCM indicates the temperature of the engine coolant, which is an indication of engine operating temperature. This sensor input is used by the PCM for fuel control, ignition timing, EGR operation, canister purge control, idle speed control, and Closed Loop fuel control. The coolant gage and the low coolant/hot lamp are controlled by the signal from the ECT sensor.
Engine Cooling Fan Control - The PCM controls operation of the engine cooling fan based on coolant temperature, air conditioning state and vehicle speed. If the coolant rises above 106°C (223°F) or if the air conditioning compressor is turned On, the PCM will supply a ground to the engine coolant fan relay, energizing the relay and engine cooling fan. The PCM will shut-off the cooling fan under the following conditions: Vehicle exceeds 97 km/h (70 mph) for three minutes. When the PCM stops receiving an A/C request signal, it will run the cooling fan for one minute, then de-energize the relay turning off the cooling fan. The A/C request signal can be removed by the operator turning the A/C switch to Off, or by the A/C high or low pressure switches opening the A/C request circuit from the A/C control head to the PCM. The cooling fan is turned On, after a initialization delay, when any of the following conditions are present: An ECT failure has been detected (DTCs P0117, P0118, P0125, P0217, P1114, P1115, and P1620). When coolant temperature exceeds 106°C (223°F) or vehicle is turned Off and ECT temperature is 110°C (230°F) or greater, the cooling fan will be turned On.
Hot/Low Coolant Telltale - The hot/low coolant telltale is one bulb used to indicate if there is a cooling system or transaxle over temperature condition failure. The hot/low coolant telltale will flash if the coolant in the bottle falls below a specified level which probably doesn't indicate an overheating problem. The light will illuminate on solid if the ECT senses engine coolant above 118°C (244°F). The light will also illuminate if the PCM calculates transaxle oil temperature to be above 140°C (284°F) or transaxle actuator temperature above 160°C (320°F) based on the transaxle oil temperature sensor and actuator ON-time. If the coolant temperature is above 118°C (244°F) and the level in the bottle is below a specified level the hot light will stay on solid.
The chart shown lists the resistances of the inlet air temperature sensor and coolant temperature sensor as compared to temperature. The sensor resistances are identical for the IAT and ECT.