Sensor Information Rover 820 Models
Lucas Hotwire Multipoint EFI
All values measured on 1990 Model 820Si.
The sensor fitted to Rover cars using the MEMS ECU and also the Honda 2.5 & 2.7 litre V6 appears to have similar electrical characteriestics.
Coolant Temperature Sensor (CTS) for ECU.
(information provided for general guidance only)
Location: On thermostat housing.
Description: Sensor plug has plug with two blade connections.
Operation: Thermistor, resistance falls as temperature increases.
| Temperature Degrees C | CTS Resistance Ohms |
| 5 | 5500 |
| 10 | 4000 |
| 15 | 3300 |
| 20 | 2500 |
| 25 | 2000 |
| 30 | 1700 |
| 40 | 1200 |
| 50 | 1000 |
| 60 | 800 |
| 70 | 600 |
| 80 | 400 |
| 85+ | 25 |
Other Useful Checks:
If engine is fully warmed up and the ECU operating correctly in a closed loop mode the engine note normally changes if the CTS is disconnected. This is a good general diagnostic test of the sensor ECU and idle stepper motor.
A 5500 ohm potentiometer in series with a 220 Ohm resistor can be used to simulate the output from the CTS. Or the sensor can simply be substituted by an 220 ohm resistor for testing purposes which would simulate a sensor at normal running temperature.