The purpose of this test is to evaluate the voltage output of an Engine Coolant Temperature (ECT) sensor as the engine coolant changes from cold to warm.
Waveform with filter applied
This known good waveform has the following characteristics:
The second example shows the same waveform with a filter added to clean up the image.
The function of the ECT sensor is to provide a measure of the engine’s coolant temperature. The signal is used by the Engine Control Module (ECM) as part of the engine load sensing apparatus. It is therefore partly responsible for the determination of fuelling, timing and engine speed requirements.
ECT sensors are manufacturer specific; despite having similar external appearances, their outputs can vary dramatically.
The majority of ECT sensors have Negative Temperature Coefficients (NTCs), meaning their internal resistance decreases as the sensing element temperature increases. Therefore, in the example above, the voltage measured across the ECT sensor drops as its resistance decreases. A Positive Temperature Coefficient (PTC) sensor will have the opposite behaviour.
The temperature sensor circuits are highly resistance sensitive, requiring a good circuit with clean connectors and no extraneous resistances: any poor/corroded connections will falsify the signal at the ECM, causing the engine to operate out of tolerance.
Selection of component-related Diagnostic Trouble Codes (DTCs):
P0115 - Engine Coolant Temperature (ECT) Sensor Circuit
P0116 - Engine Coolant Temperature (ECT) Sensor Performance
P0117 - Engine Coolant Temperature (ECT) Sensor Circuit Low Voltage
P0118 - Engine Coolant Temperature (ECT) Sensor Circuit High Voltage
P0119 - Engine Coolant Temperature Circuit Intermittent
P0125 - Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control
P1114 - Engine Coolant Temperature (ECT) Sensor Circuit Intermittent Low Voltage
P1115 - Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage
P1116 - ECT Signal Unstable or Intermittent
P1117 - Engine Coolant Temp. Signal Out-Of-Range Low
P1118 - Engine Coolant Temp. Signal Out-Of-Range High
P1119 - ECT Signal Out-Of-Range With TFT Sensor
P1258 - Engine Coolant Overtemperature - above 268°F - Protection Mode Active
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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