The coolant temperature sensor is located on the left side of the cylinder block, just below the exhaust manifold. The CTS provides an engine coolant temperature input to the ECU, which will then enrich the air/fuel mixture delivered by the injectors when the engine coolant is cold. Based on the CTS signal, the ECU will also control engine warmup idle speed, increase ignition advance and inhibit EGR operation when the coolant is cold.
See Figure 1
Disconnect the wire harness connector from the CTS and measure the resistance of the sensor with a high input impedance (digital) volt-ohmmeter. The resistance should be less than 1000 ohms with the engine warm. Refer to the resistance chart and replace the sensor if it is not within the range of resistance specified in the chart. Measure the resistance of the wire harness between ECU wire harness connector terminal D-3 and the sensor connector terminal, and terminal C-10 to the sensor connector terminal and repair the wire harness if an open circuit is indicated.