In modern engines, the coolant temperature sensor, and in a few cases, the oil temperature sensor, perform a very important task. They provide information and inform whether the engine has reached the normal operating temperature or it is just warming up to the controller. The information provided by the coolant temperature sensor (oil) determines the way, the injection system is controlled. Therefore, it is very important that the fluid (oil) temperature sensor circuit works properly. It is a common practice that mechanics check only the sensor resistance to the respective temperatures. It is not enough as in some cases, despite the fact that the sensor controller is working properly, the signal provided to the controller is distorted. This may result from the fact that the resistance is too high or there is a sensor short circuit or even the controller itself is damaged.
The SCR-3V DeltaTech Electronics sensor simulator makes a very useful instrument for diagnosing the temperature sensor circuit of the coolant, oil, air and CO controls and potentiometric sensors. This new and original solution provided by this company allows the simultaneous simulation and observation of the voltage signal in the sensor circuit by means of a single device. It is functional and very important because voltage is the most important parameter of the sensor circuit and not only the sensor resistance itself. The table presents the most common dependence of resistance and voltage in relation to the temperature function.
|Temperature (degree C)||Resistance (Ohm)||Voltage (V)|
|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|
|40||1000 to 1200||2,50 to 3,00|
|60||800||2,00 to 2,50|
|80||270 to 380||1,00 to 1,30|
|110||180 to 200||0,50|
|Break in the circuit||–||5,00|
|Short to ground||–||0|
While conducting the temperature simulation, e.g. from lowest to highest, together with simultaneous measurement of the injection times and exhaust gas analysis, it is possible to test the injection system thoroughly. We do not have to waste time, as it has been so far and wait for the engine to cool down.
To simulate the simulation e.g. of a temperature sensor, follow these steps:
- locate the temperature sensor and disconnect the sensor wires,
- connect the simulator endings to the wires disconnected from the sensor,
- set the simulator to the resistance value corresponding to the cold engine (according to the factory specifications),
- start the engine – it should work at a higher speed (as if the engine was cold.) If the engine is warm, the resistance value (voltage) can be changed from the one corresponding to a cold engine, for example 6000 ohms (4th .. 4.5 V) to the value corresponding to a warm engine e.g. 300 Ohm (1st .. 1.5 V). The engine shall respond by increasing the speed typical of the “cold engine” simulation and by reducing it to a normal idle speed typical of the “warm engine” simulation,
- turn off the engine, disconnect the simulator endings, and connect the cables to the temperature sensor.
If the engine does not respond to the temperature simulation in the way specified by the manufacturer, it means that the temperature sensor circuit is out of order or the controller is damaged. The most common and proper reaction to the “cold engine” simulation is increasing the speed and enriching the fuel-air mixture, whereas the simulation of normal operating temperature should cause the motor to move to the idle speed value and the mixture composition set by the factory (provided the engine is really set to the operating temperature).
Another unquestionable advantage of the SCR-3V simulator is the possibility of confirming the failure of a given sensor before deciding on its replacement.
The SCR-3V simulator due to its uncomplicated operation and a very reasonable price is available even for small garages.