Freelander System Description and Operation
ENGINE MANAGEMENT SYSTEM - SIEMENS
18-4-22 DESCRIPTION AND OPERATION
ECT Sensor
The ECT sensor provides the ECM with a signal voltage that varies with coolant temperature, to enable the ECM to
adapt the fuelling quantity and ignition timing with changes of engine temperature.
The ECT sensor is located between the cylinder banks, between cylinders 3 and 6.
The ECT sensor consists of an encapsulated Negative Temperature Coefficient (NTC) thermistor which is in contact
with the engine coolant. As the coolant temperature increases the resistance across the sensor decreases and as the
coolant temperature decreases the sensor resistance increases. To determine the coolant temperature, the ECM
supplies the sensor with a regulated 5 volts power supply and monitors the return signal voltage. The ECM also
outputs the coolant temperature on the CAN system, to operate the coolant temperature gauge.
If the ECT signal is missing, or outside the acceptable range, the ECM assumes a default temperature reflecting a
part warm engine condition. This enables the engine to function, but with reduced driveability when cold and increased
emissions, resulting from an over rich mixture, when the engine reaches normal operating temperature. The ECM will
also switch on the cooling fans to prevent the engine and gearbox from overheating.
The following table shows engine coolant temperature values and the corresponding ECT sensor resistance values.
Engine coolant Temperature
°
C (
°
F)
Sensor Resistance k
Ω
- 40 (- 40)
75.501
- 30 (-22)
39.764
-20 (-4)
21.883
-10 (14)
12.452
0 (32)
7.353
10 (50)
4.482
20 (68)
2.814
30 (86)
1.814
40 (104)
1.199
50 (122)
0.8109
60 (140)
0.5601
70 (158)
0.3945
80 (176)
0.2829
90 (194)
0.2064
100 (212)
0.1529
110 (230)
0.1149
120 (248)
0.08761
130 (266)
0.06762
140 (284)
0.05281
150 (302)
0.04171