The purpose of this test is to evaluate the correct operation of a Coolant Temperature Sensor (CTS) responding to a change in coolant temperature from cold to warm.
The Example Waveform shows a gradual voltage reduction as engine coolant temperature rises.
The second example shows the same waveform with a filter added to clean up the image.
NOTE; the starting voltage is dependant on coolant temperature at the beginning of the test.
The Coolant Temperature Sensor (CTS) is a small two pin sensor whose job is to report the engine temperature back to the ECM. It is this signal that determines the engine warm up, enrichment and fast idle duration.
NTC sensors are predominantly made from a sintered semi-conductor material which will decrease electrical resistance in reaction to temperature rise. When installed into an engine cooling system it will provide an accurate voltage change as the coolant heats up.
The ECM is therefore provided with a signal which will allow accurate control throughout the operating temperature range.
Coolant temperature sensors are manufacturer specific and although the units may look identical the outputs vary dramatically.
All temperature sensors are resistance sensitive. Which means they require a clean circuit. Any poor/corroded connections will introduce an extra resistance in series and will falsify the readings that the ECM sees. Even though the sensor input may be within ECM parameters, not recording any faults, the engine will not operate as designed.
This help topic is subject to changes without notification. The information within is carefully checked and considered to be correct. This information is an example of our investigations and findings and is not a definitive procedure. Pico Technology accepts no responsibility for inaccuracies. Each vehicle may be different and require unique test settings.
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