In modern engines, the coolant temperature sensor and, in a few cases, the oil temperature sensor performs a very important task. It provides the controller with information such as whether the engine has already reached normal operating temperature or is just warming up. The information provided by the coolant (oil) temperature sensor determines how the injection system is controlled. Therefore, it is very important that the fluid (oil) temperature sensor circuit works properly. It is very common for mechanics to check only the resistance of the sensor itself for the corresponding temperatures. This is an insufficient check, because in some cases, despite a functioning temperature sensor, the controller receives a falsified signal. This may be due to excessive resistance or short circuits in the sensor circuit or even failure of the controller itself. A very helpful instrument for diagnosing the circuit of coolant, oil, air temperature sensors, as well as CO controllers and potentiometer sensors is the SCR-3V sensor simulator from DeltaTech Electronics. This new and original solution from this company makes it possible to simultaneously simulate and observe the voltage signal in the sensor circuit with a single device. This is functional and very important because in sensor circuits the most important parameter is the voltage, not the resistance of the sensor itself. The table shows the most common dependencies of resistance and voltage as a function of temperature.
| Temperature (degree C) | Resistance (Ohm) | Voltage (Volt) |
|---|---|---|
| 0 | 4600 to 6600 | 4.00 to 4.50 |
| 10 | 4000 | 3.75 to 4.00 |
| 20 | 2200 to 2800 | 3.00 to 3.50 |
| 30 | 1300 | 3,25 |
| 40 | 1000 to 1200 | 2,50 to 3,00 |
| 50 | 1000 | 2,50 |
| 60 | 800 | 2.00 to 2.50 |
| 80 | 270 to 380 | 1.00 to 1.30 |
| 110 | 180 to 200 | 0,50 |
| Circuit break | – | 5,00 |
| Short circuit to ground | – | 0 |
By simulating the temperature, for example, from lowest to highest, along with simultaneous measurement of injection times and analysis of the exhaust gas, we can accurately check the performance of the injection system. At the same time, we don’t have to waste time waiting for the engine to cool down, for example. To simulate, for example, a temperature sensor, perform the following steps: – locate the temperature sensor and disconnect the wires, – connect the ends of the simulator to the wires disconnected from the sensor, – set the resistance value on the simulator corresponding to a cold engine (according to the factory data), – start the engine – it should run at increased speed (as with a cold engine). If the engine is warm, we can change the resistance (voltage) value from that corresponding to a cold engine, e.g. 6000 Ohms (4…4.5V) to that corresponding to a heated engine, e.g. 300 Ohms (1…1.5V). The engine should respond by raising the RPM for the “cold engine” simulation and lowering it to normal idle speed for the “heated engine” simulation. – Turn off the engine, disconnect the simulator terminals, connect the cables to the temperature sensor. If the engine does not respond to the temperature simulation as specified by the manufacturer, it means that the temperature sensor circuit is faulty or the controller is defective. The most common, and correct, response to simulating a cold engine is to raise the RPM and enrich the air-fuel mixture, while simulating a normal operating temperature should cause the engine to shift to the factory-set RPM and mixture composition values (if the engine is actually at operating temperature, of course). Another unquestionable advantage of the SCR-3V simulator is the ability to ascertain the malfunction of a particular sensor before deciding whether to replace it. The SCR-3V simulator is available even to small auto repair shops due to its uncomplicated operation and very affordable price.
23% VAT should be added to the quoted price.
