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.
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HOMESERVICE MANUALSJEEP1999CHEROKEE 4WD L4-2.5L VIN PREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSCOOLANT TEMPERATURE SENSOR/SWITCH (FOR COMPUTER)DESCRIPTION AND OPERATION
1999 Jeep Cherokee 4WD L4-2.5L VIN P
Coolant Temperature Sensor/Switch (For Computer): Description and Operation
1999 Jeep Cherokee 4WD L4-2.5L VIN PSECTION Description and Operation
ENGINE COOLANT TEMPERATURE SENSOR-PCM INPUT
The engine coolant temperature sensor is installed in the thermostat housing and protrudes into the water jacket. The sensor provides an input voltage to the Powertrain Control Module (PCM) relating coolant temperature. The PCM uses this input along with inputs from other sensors to determine injector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor's resistance changes. The change in resistance results in a different input voltage to the PCM.
When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer airfuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.
Refer to Open Loop/Closed Loop Modes of Operation for more information.
Engine Coolant Temperature Sensor - Typical:
The engine coolant temperature sensor is installed in the thermostat housing and protrudes into the water jacket. The sensor provides an input voltage to the Powertrain Control Module (PCM) relating coolant temperature. The PCM uses this input along with inputs from other sensors to determine injector pulse width and ignition timing. As coolant temperature varies, the coolant temperature sensor's resistance changes. The change in resistance results in a different input voltage to the PCM.
When the engine is cold, the PCM will operate in Open Loop cycle. It will demand slightly richer airfuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached.
Refer to Open Loop/Closed Loop Modes of Operation for more information.
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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.