Coolant temperature sensor - GM/Vauxhall/Opel Simtec

The purpose of this test is to evaluate the correct operation of a Coolant Temperature Sensor (CTS) responding to a change in coolant temperature during the engine warming phase. 

Connection guidance

Connection for diagnostic work will vary dependent on application.

Technicians should whenever possible gain access to the test circuit without damage to seals and insulation. If this is not possible then make sure appropriate repairs are completed.

General connection advice

PicoScope offers a range of options within the test kits.

Dependent on difficulty of access, choose from

  1. Breakout leads.
  2. Back-pinning probes.

Testing Sensors and Actuators (to include relevant circuit/connectors):

  • When testing a sensor, it is desirable to gain access at the control unit.
  • When testing an actuator, it is desirable to gain access at the actuator.

How to perform the test

  1. Connect PicoScope Channel A to the 5V supply for the coolant sensor.
     
  2. A good earth is required connecting to the battery negative terminal will check out the earth circuit.
     
  3. Start the engine and run at idle.
     
  4. Minimise the help page and with the example waveform on your screen PicoScope has already selected suitable scales for you to capture a waveform.
     
  5. Select GO or press the space bar to see live data.

Example waveform

Waveform notes

You can see in the Example Waveform that the sensor is a Negative Temperature Coefficient type (NTC), the voltage falls as the coolant temperature increases.

At a voltage relative to 40 to 50°C the Engine Control Module (ECM) increases the sensor supply voltage. The voltage then continues to fall as coolant temperature rises. The manufacturer states that this gives a finer control.

Further guidance

Technical Information

The CTS 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. 

Generic DTC’s Coolant Temperature Sensor.

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

GT016-4

Disclaimer
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.

Suitable accessories

  • Premium 6-way breakout lead set

    £269.00

  • 2 Pin AMP connector breakout lead

    £30.00

  • Back-pinning Probe Set

    £40.00

  • Flexible Back-pinning Probe

    £3.00

  • Large Dolphin/Gator Clips

    £10.00

  • Premium Test Lead: BNC to 4 mm, 3 m

    £47.00

  • Premium Test Leads: Set of four leads 3 m (TA125 - TA128)

    £179.00

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Guided test: Vauxhall Simtec