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This is a good waveform |
| Vehicle: |
Vauxhall |
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Coolant Temperature Sensor – Vauxhall Waveform Notes
In this particular instance we are observing the relationship between the signal from the Crank Angle Sensor (CAS) and the Camshaft Sensor or Cylinder Identification sensor (CID).
The Coolant Temperature Sensor (CTS) on this particular vehicle has completely different voltage characteristic to that on an a conventional system. On the conventional CTS, the voltage will be seen to drop as the engine temperature increases. When cold the voltage will be approximately 3 to 4 volts, once normal operating temperature is achieved this voltage will be around 1 volt. The quoted voltages are however manufacturer specific. Most temperature sensors will have a Negative Temperature Coefficient (NTC) so the voltage decreases with an increase in engine temperature. Positive Temperature Coefficient (PTC) sensors will have an increasing voltage as the temperature rises.
The CTS used in the Multec system on the Vauxhall Vectra 1.6 Lt. engine has a distinctive waveform when viewed on the oscilloscope. The voltage seen at the CTS will display a conventional voltage reduction, until the engine reaches 40 - 50 °C at which point the voltage rises dramatically due to internal switching inside the Electronic Control Module (ECM). The reason for the voltage change is that at higher operating temperatures (50 °C plus), the ECM is now able to offer finer control with the increased voltage.
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