Jeep Wrangler/YJ 1987-1995 Repair Guide

Coolant Temperature Sensor (CTS)


The CTS is located in the intake manifold coolant jacket and provides an engine coolant temperature signal to the ECU. The ECU uses the coolant temperature signal to enrich the air fuel mixture when the engine is cold, compensate for fuel condensation in the intake manifold, control engine warm-up speed, increase the ignition advance when the engine is cold and cut off the EGR system when the engine is cold.


See Figure 1

The CTS is tested in the same manner as the MAT sensor, and should yield the same results. The only difference is the pin number of the test points.

  1. Unplug the wire harness connector from the sensor, then test the resistance of the sensor with a digital volt-ohmmeter. The resistance should be less than 1000 ohms with the engine warm. Refer to the chart to check the temperature-to-resistance values and replace the sensor if the resistance is not within the specified range.
  3. Test the resistance of the wire harness between ECU wire harness connector terminal 15 and the sensor connector terminal; also test the resistance between ECU wire harness connector terminal 32 and the sensor connector terminal. Repair the wire harness as necessary if an open circuit is indicated.

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Fig. Fig. 1: MAT sensor and CTS temperature-to-resistance-values


See Figure 2

  1. Detach the CTS electrical connector.
  3. Remove the CTS from the intake manifold, then immediately plug the hole to prevent coolant loss.
  5. Installation is the reverse of removal. Tighten the CTS to 21 ft. lbs. (28 Nm).

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Fig. Fig. 2: The coolant temperature sensor screws into the intake manifold