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ABS Speed Sensor
Air Flow Meter / Sensor
Air Intake Pressure Sensor
Alternator Current and Voltage
Amplifier Earth
Camshaft Sensor
Carbon Canister Solenoid Valve
Crankshaft sensor
Coolant Temperature sensor
Diesel Glow Plugs
Digital ECM to Ignition Amplifier Signal
Distributor Pickup
Dual Trace
Electronic Fuel Pump
Exhaust Gas Recirculation
Idle Speed Control Valve
Knock Sensor
Lambda Sensor
MAP Sensor
Relative Compression
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Coolant Temperature Sensor - Waveform Notes

The Coolant Temperature Sensor (CTS) will invariably be a two wire device with a voltage supply.

The sensor itself has the ability to alter its resistance with engine temperature change. The majority of sensors have a Negative Temperature Coefficient (NTC) which results in the resistance of the component decreasing as the temperature increases.

The resistance change will therefore alter the voltage seen at the sensor and can be monitored for any discrepancies across its operational range. As the temperature increases the resistance decreases and the voltage will also be seen to drop.

The rate of voltage change is usually linear with no sudden changes to the voltage.

NOTE :- The Vauxhall Simtec system has a point at which the voltage alters dramatically during the warm up period, this is described in the Coolant Temperature Sensor (Vauxhall) waveform page.

Technical Information

The sensors are manufacturer specific and the outputs will vary dramatically although they may look identical. Any poor connections on this circuit will introduce an extra resistance in series and will falsify the readings that the ECM sees, reading the resistance at the ECM's multi-plug will confirm this.

Here is a typical coolant temperature sensor.