Cold Diesel and Gasoline Start in cold.

Greetings to this community!

I've been having problems with cold starts on both diesel and gasoline engines.
From what I understand, the ECU uses information from the engine coolant temperature sensor (NTC) and the intake air temperature sensor for cold starts. If I'm not mistaken, and I'm sure I'm missing something, this is true for newer systems.

In gasoline vehicles, the module injects more fuel, increasing the idle speed.

In diesels, it controls the glow plug relay timing to heat the combustion chambers (in addition to newer systems that preheat the diesel fuel).

If I disconnect these sensors on gasoline engines, I don't see the idle speed increase to induce a cold start; instead, the cooling fans come on (Opel Astra G Z16SE)

. And in diesels, which sensors inform the module to activate the glow plug relay? The coolant temperature sensor (NTC) is one, and what others are involved?

Could you please clarify and help me?
How to induce a cold start on a gasoline engine? Could I trick the ECU with resistors on the sensors? Although disconnecting them only activates the fan, creating infinite resistance.

And how to trick the diesel ECU into activating the glow plug relay? Because when the engine is hot, the ECU receives information from the hot engine and stops activating the relay. (There was a problem with Peugeot, and they bypassed the temperature sensor.) This is a comment that was made to me. I'm sure it will be useful.

Sorry for the long post.
Best regards and many thanks to everyone.

Hi piter112, regarding: "in gasoline vehicles the module injects more gasoline and the idle speed increases," this happened in older systems. Because the engine temperature parameter was missing, the module assumed the engine was cold, therefore enriching the mixture and significantly increasing the revolutions per minute (RPM). The electric fans don't turn on when the temperature sensor is disconnected because the ventilation function is controlled by a bulb that was usually located in the radiator.

Regarding: "if I disconnect these sensors in a gasoline engine, I don't see the idle speed increase to force a cold start; instead, the fans come on (Opel Astra G Z16SE)," this is the normal behavior of a modern system when it lacks the coolant temperature parameter. In these systems, the lost signal is replaced by a value derived from the other parameters. For example, air temperature, oil temperature, calculated load, time elapsed since start-up, throttle position, vehicle speed, gear position, atmospheric pressure, oxygen sensor, etc. From this, the module calculates a statistically most probable value for the lost signal, e.g., 80 degrees. While the control quality is degraded, it's not as much as in the previous case. Since the engine control module doesn't know the engine temperature, it activates the electric fans to prevent overheating, because in this case, the engine control unit (ECU) is responsible for the fan function and speed, primarily based on the coolant temperature.

Regarding: "Could you advise and help me
on how to induce a cold start in a gasoline engine? Could I trick the ECU with resistors on the sensors? Although disconnecting only activates the fan, creating infinite resistance, it can be done with a potentiometer or variable resistor connected to the temperature sensor connector. However, be careful with the resistive ranges, and any changes must be gradual.

In modern diesel engines, the combustion chamber preheating function is generally controlled by a preheating control module, which calculates the time based on information from other modules. The most important are the coolant temperature, intake air temperature, diesel temperature, barometric pressure, etc., all provided by the engine control module. However, there are other important parameters such as battery voltage, battery temperature, presence of other electrical consumers, etc., which can be provided by other modules, e.g., the BCM. I have also seen systems where it is..." The preheating function is controlled by the engine control module (ECM), or the engine management module (EMM), but it always uses the same information to calculate the time.
Therefore, if you want to trick the system, the newer the engine, the more difficult it generally is, although it's always possible, mainly due to the quality and quantity of information they have to calculate the most appropriate responses. In short, to simulate features like cold starts, you need to be clear about which module controls the function, what information it uses, and the channels through which it transmits that information. Best of luck.

Hi piter112, regarding: "in gasoline vehicles the module injects more gasoline and the idle speed increases," this happened in older systems. Because the engine temperature parameter was missing, the module assumed the engine was cold, therefore enriching the mixture and significantly increasing the revolutions per minute (RPM). The electric fans don't turn on when the temperature sensor is disconnected because the ventilation function is controlled by a bulb that was usually located in the radiator.

Regarding: "if I disconnect these sensors in a gasoline engine, I don't see the idle speed increase to force a cold start; instead, the fans come on (Opel Astra G Z16SE)," this is the normal behavior of a modern system when it lacks the coolant temperature parameter. In these systems, the lost signal is replaced by a value derived from the other parameters. For example, air temperature, oil temperature, calculated load, time elapsed since start-up, throttle position, vehicle speed, gear position, atmospheric pressure, oxygen sensor, etc. From this, the module calculates a statistically most probable value for the lost signal, e.g., 80 degrees. While the control quality is degraded, it's not as much as in the previous case. Since the engine control module doesn't know the engine temperature, it activates the electric fans to prevent overheating, because in this case, the engine control unit (ECU) is responsible for the fan function and speed, primarily based on the coolant temperature.

Regarding: "Could you advise and help me
on how to induce a cold start in a gasoline engine? Could I trick the ECU with resistors on the sensors? Although disconnecting them only activates the fan, creating "infinite resistance," it can be done with a potentiometer or variable resistor connected to the temperature sensor connector. However, be careful with the resistive ranges, and any changes must be gradual.

In modern diesel engines, the combustion chamber preheating function is generally controlled by a preheating control module, which calculates the time based on information from other modules. The most important are the coolant temperature, intake air temperature, diesel temperature, barometric pressure, etc., all provided by the engine control module. However, there are other important parameters such as battery voltage, battery temperature, presence of other electrical consumers, etc., which can be provided by other modules, e.g., the BSI. I have also seen systems where it is..." The preheating function is controlled by the engine control module, or the electronic control module (BSI) in Citroën vehicles, but it always uses the same information to calculate the time.
Therefore, if you want to trick the system, the newer the vehicle, the more difficult it is, although it's always possible, mainly due to the quality and quantity of information they have to calculate the most appropriate responses. In short, to simulate features like cold starts, you need to know which module controls the function, what information it uses, and the channels through which it transmits that information. Best of luck.