Jeep 56004815 Sensor-COOLANT Temperature

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The coolant temperature indicating system consists of a sending unit which is screwed into the cylinder head or manifold and a corresponding temperature gauge mounted in the instrument panel. When the coolant temperature of the engine is low the resistance of the sending unit is high and restricts the flow of current to the gauge. This causes the pointer to move only a short distance. As the temperature of the coolant increases, the resistance at the sending unit decreases and causes an increased flow of current and movement at the gauge. Do not apply 12 volt current directly to the temperature sender terminal at any time, as the voltage will damage the unit. Start the engine and allow it to run with a thermometer placed in the radiator neck until a minimum temperature of 180°F is read. The gauge in the instrument panel should indicate within the normal band of the reading scale. If the gauge does not indicate correctly, disconnect the gauge lead from the terminal at the sender unit. Connect the lead of a 12-volt test light or the positive lead of a voltmeter to the gauge lead that was disconnected. Connect the other test lead to an engine ground. With the ignition switch set to the On or Accessory position, a flashing light or fluctuating voltage should indicate that the instrument voltage regulator is operating and the gauge circuit is not grounded. If the light stays on or the voltage reading is steady, the instrument voltage regulator is bad. If no voltage is indicated by the voltmeter or test light, check for an open circuit in the system. If all of the above readings check out correctly yet the gauge does not work properly, the gauge sender needs replacement. The engine must be completely cool when this procedure is performed. Disconnect the wire from the unit. Use a wrench to remove the old unit and immediately install the new one. Because the unit threads into a coolant passage, there will be some coolant spillage. Check the level after the replacement has been installed.

The coolant temperature indicator system includes a dashboard light or gauge and a sending unit on the engine. Some vehicles have multiple sending units, but only one is used for the indicator. If the car has an electric cooling fan, avoid the fan blades as they can start unexpectedly. If overheating is indicated, check the coolant level, ensure secure wiring between the light/gauge and sending unit, and check all fuses. To test, ground the wire to the sending unit with the ignition on. Once the engine starts, the light should go out unless the engine overheats. If it doesn't, it could be a grounded wire, defective sending unit, or faulty ignition switch. Check the coolant type, as plain water may not activate the sending unit. If replacing the sending unit, unscrew it from the engine and install the replacement with sealant on the threads. Let the engine cool before removal and expect some coolant loss. Check the coolant level after replacement.

Information sensors provide data on engine conditions, aiding in fuel economy and emission reduction. The oxygen sensor in the exhaust manifold measures oxygen content in the exhaust, adjusting the fuel/air mixture. The knock sensor detects engine detonation, retarding ignition timing. The coolant temperature sensor monitors temperature for fuel/air mixture adjustments. The manifold absolute pressure sensor reads pressure changes to vary the air/fuel mixture. The manifold air temperature sensor measures air temperature for fuel/air adjustments. The crankshaft position sensor detects engine speed for ignition timing and fuel control. The vehicle speed sensor determines vehicle speed.

For the crankshaft reference sensor, unplug the electrical connector, loosen the retaining bolt, remove the sensor, and if reinstalling, remove the old spacer and install a new one.

Failure of the light to go out when the engine starts may be caused by a grounded wire, defective sending unit, or faulty ignition switch.

The throttle position sensor (TPS) helps the ECM determine fuel delivery based on the angle of the throttle valve. Its resistance is tested using an ohmmeter. The resistance should be progressive as you move the throttle. An inconsistent resistance reading may indicate a faulty TPS.