Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
1991 Jaguar XJ-6 L6-4.0LSECTION Description and Operation
The coolant temperature sensor, located on the thermostat housing, is a negative temperature coefficient (NTC) thermistor. NTC means that the resistance of the thermistor decreases as the sensed temperature increases. Pin 1 of the sensor is connected to ground through the ECM. The ECM applies 5 volts to pin 2 of the sensor and monitors the voltage across the sensor pins. The theoretical full voltage range is from 5 to 0 volts representing maximum cold to maximum hot.
The ECM converts the monitored voltage into a digital number that relates to an engine coolant temperature. The temperature signal is then used for a number of functions:
- Cranking enrichment.
- Warm-up enrichment.
- Acceleration enrichment.
- Air injection.
- Idle speed control.
- Enable EGR.
- Evaporative canister purge.
NOTE: Other sensor inputs are required for the initiation of most of the above listed ECM functions.
The ECM converts the monitored voltage into a digital number that relates to an engine coolant temperature. The temperature signal is then used for a number of functions:
- Cranking enrichment.
- Warm-up enrichment.
- Acceleration enrichment.
- Air injection.
- Idle speed control.
- Enable EGR.
- Evaporative canister purge.
NOTE: Other sensor inputs are required for the initiation of most of the above listed ECM functions.
Temperature Versus Resistance And Voltage:
RENDER: 1.0x
NO RELATED
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.