SW1 L4-1.9L SOHC VIN 8 (1996)
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
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.
