The purpose of this test is to evaluate the correct operation of an Electronic Coolant Temperature (ECT) sensor responding to a change in coolant temperature during the engine warming phase.
This known good waveform has the following characteristics:
The sensor is a Negative Temperature Coefficient type (NTC), where the output voltage falls as the coolant temperature increases.
At a voltage in the range 40-50°C the Engine Control Module (ECM) increases the sensor supply voltage. The voltage then continues to fall as coolant temperature rises.
The ECT is a small two pin sensor its function is to provide a voltage relative to coolant temperature back to the ECM. It is this signal that determines the engine warm up, enrichment and fast idle duration.
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.
The General Motors Simtec Sensor on this vehicle has a different voltage characteristic to that on the majority of vehicle systems.
The GM/Vauxhall/Opel Vectra 1.6 litre engine uses this sensor and therefore has a distinctive waveform when viewed on the oscilloscope. The manufacturer states that this gives a finer control.
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
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