Circuit Test ECT - Engine Coolant Temperature Sensor

WARNING: This page is about a different car, the 1994 Mercury Tracer and 1994 Ford Escort. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: ECT Sensor Circuit & Connector Terminal ID (1.8L ECT)

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
A/T
ECT	7	2E	Blue/White
SIG RTN	46	3D	Black/White
M/T
ECT	7	2Q	Blue/White
SIG RTN	46 & 49	2D	Black/White

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 using Rotunda Digital Thermometer (055-00100). Turn ignition off. Install breakout box, leaving PCM disconnected. Measure resistance between ECT and SIG RTN 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. Measure and record resistance between ground and ECT test pin at breakout box. If resistance between ECT test pin at breakout box and ECT terminal at ECT sensor connector is less than 5 ohms and resistance between ground and ECT test pin at breakout box is greater than 10,000 ohms, go to next step. If resistance is not as specified, repair ECT wire between ECT sensor connector and PCM.

4) Check SIG RTN Circuit Ensure ignition is off and ECT sensor is disconnected. With breakout box installed and PCM disconnected, measure resistance between SIG RTN test pin at breakout box and SIG RTN terminal at ECT sensor connector. If resistance is less than 5 ohms, replace ECT sensor. If resistance is 5 ohms or more, repair SIG RTN wire between ECT sensor connector and PCM.