The coolant temperature sensor is a thermistor; a temperature controlled variable resistor with a range of -40°-265°F (5°-129°C) mounted in the engine coolant stream. The PCM uses the temperature input to adjust the fuel mixture slightly richer and raise the idle speed, until normal operating temperatures are reached. On all models, this sensor is also used to control the cooling (radiator) fan operation.
The PCM supplies 5.0 volts to the coolant temperature sensor. The sensor provides an input voltage to the PCM. As coolant temperature varies, the sensor resistance changes resulting in different input voltage to the PCM.
When the engine is cold, the PCM will demand slightly richer air/fuel mixtures and higher idle speeds until normal operating temperatures are reached.
See Figures 1 and 2
Before testing any electrical component, inspect the wiring and connectors for damage. Also wiggle the connectors to ensure a that they are firmly engaged.
- Make certain that the engine is cool (i.e. has not been run for a couple of hours).
- Unplug the engine wiring harness electrical connector from the coolant temperature sensor.
- Connect an ohmmeter between the terminals A and B of the sensor.
- At room temperature (70° F) the ohmmeter should read approximately 7000-13,000 ohms.
- If the resistance readings are not within specifications, replace the sensor with a new one.
- Attach the engine wiring harness electrical connector to the coolant temperature sensor, then turn the engine ON (without starting the engine).
- Backprobe the sensor's tan/black tracer wire to ground with a voltmeter. Refer to the accompanying wiring illustration. Then start the engine.
Watch the voltage of the sensor until the engine coolant reaches normal operating temperature.
- If the voltage does not change, or changes in erratic jumps the sensor is defective and will need replacing.
- If the voltage changes gradually and in a smooth manner, continue to the next step.
- Once the coolant temperature has reached normal operating temperature, turn the engine OFF but keep the ignition ON .
- Unplug the engine wiring harness electrical connector from the coolant temperature sensor again.
- Connect the ohmmeter between the terminals of the sensor. The sensor resistance should be between 700-1000 ohms at 200 ° F.
- If the sensor has not functioned as described in any of the various steps, replace the sensor with a new one.
- Make sure to retest once the new sensor has been installed to rule out the possibility of numerous problem spots.
REMOVAL & INSTALLATION
See Figures 3 and 4
The engine coolant temperature sensor is located next to the thermostat housing.
- Unplug the electrical connector from the coolant temperature sensor.
- Drain the coolant system until it is below the level of the sensor. Make certain to drain the fluid into a large, clean vessel so that it may be used later.
- Unscrew the sensor from the thermostat housing or intake manifold (next to the thermostat housing).
- Start the sensor into its hole slowly, making sure that the threads are not crossthreading. Screw the sensor as far as possible by hand.
- Tighten the sensor to 21 ft. lbs. (28 Nm).
- Connect the coolant temperature sensor's electrical plug to the wiring harness.
- Remove the shop towels from the pulleys and drive belts.
- Refill and bleed the coolant system. For more details, Refer to General Information & Maintenance .
- Start the vehicle and check for coolant leaks.