Engine Coolant Temperature Sensor

NOTE: Enter this test only when a Code 09 is displayed during self-test procedures (KOEO or KOER) or when directed here from another circuit test. To prevent unnecessary diagnosis, inspect coolant level, oil level, cooling fan, thermostat and airflow to radiator for obstruction before electronic testing. This test is intended to diagnose ECT circuit only.

CIRCUIT PIN IDENTIFICATION

Circuit	Breakout Box Pin No.	PCM Pin	Wire Color
ECT	7	2E	Red/Green
GND	46	3D	Black/Blue

1) Check System Integrity Visually check all wiring, connectors and components for evidence of damage, shorting or looseness. If a fault is found, repair as necessary. If no fault is found, go to next step.

2) Check ECT Sensor Resistance Run engine until engine coolant reaches temperatures specified. See RESISTANCE SPECIFICATIONS (ECT SENSOR) table. Monitor temperature at ECT sensor (near thermostat housing) using Rotunda Digital Thermometer (055-00100) or equivalent. Turn ignition off. Install breakout box, leaving PCM disconnected. Measure resistance between ECT and GND test terminals at breakout box. Compare readings with RESISTANCE SPECIFICATIONS (ECT SENSOR) table. If resistance is not as specified, go to next step. If resistance is as specified, ECT circuit is okay. If no other problem or code is found, replace PCM.

RESISTANCE SPECIFICATIONS

Temperature °F (°C)	Ohms
68 (20)	2200-2700
104 (40)	1000-1300
140 (60)	500-650
176 (80)	250-350

3) Check ECT Circuit Turn ignition off. With breakout box installed and PCM disconnected, disconnect ECT sensor connector. Measure and record resistance between ECT test pin at breakout box and ECT terminal at sensor connector. See Fig 2. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open wire between ECT sensor connector and PCM.

4) Ensure no continuity exists between ECT test pin at breakout box and ground or between ECT test pin at breakout box and SIG RTN test pin at breakout box. If continuity is present between ECT circuit and any other circuit, repair ECT wire between ECT sensor connector and PCM. If no continuity is present between ECT circuit and any other circuit go to step 6).

NOTE: A break in the step numbering sequence occurs at this point. No steps have been omitted.

6) Check Ground Circuit Ensure ignition is off and ECT sensor is disconnected. Measure resistance between ground and GND terminal at ECT sensor connector. If resistance is less than 5 ohms, replace ECT sensor. If resistance is 5 ohms or more, repair GND wire between ECT sensor connector and PCM.

Fig 1: Identifying ECT Sensor Circuit

Fig 2: Identifying ECT Connector Terminals