Safe Mode

[MNBoxster]

Originally Posted by CJ_Boxster

Safe mode on your car is called "Closed Loop Mode", when you have a CEL on, your car will go from Open Loop, to Closed Loop, and the ECU will run on its lower performance fuel map to lower the risk of damaging other components.

Hi,

Actually, this is not true. You have Open Loop and Closed Loop confused.

Open Loop mode simply means that the ECU does not monitor the O² and other sensors to adjust fuel delivery – it is not receiving or using ‘feedback’ from the engine sensors, therefore, it's really not a Loop at all, but that's what they call it nonetheless.

Closed Loop means the ECU (DME in Porsche parlance) monitors the O² and other sensor voltages and adjusts the fuel injector pulse width and Spark Timing accordingly to meet the sensed conditions using a number of target Maps designed for performance, load, etc.

In Open Loop mode, the 0² sensor is not controlling the mixture. Typically this occurs during warmup before the sensor is up to operating temperature, and also at WOT. In Open Loop the mixture is controlled by the ECU applying default maps. This is what happens in SAFE MODE (this is a misnomer, it is more accurately a Default Mode). The sensors input is outside of the pre-programmed parameters and the DME doesn't know what to do so it goes to it's default mode. This is more to maintain low emissions than any protective function, this usually results in less performance, but only to keep emissions as low as possible.

In Closed Loop the DME is reading the 0² sensors along with other sensors and using their signals to adjust Mixture and Spark. It's referred to as Closed Loop because it's a "feedback" system, where the ECU constantly reads the sensors, makes adjustments, checks the results, etc. hundreds or thousands of times a second.

If you are having issues which cause the car to stay in Open Loop operation, this probably does not have anything to do with starting, look for other coincidental causes here. Open Loop s/b one of the most start-friendly Fuel/Spark Maps. Hope this helps...

Happy Motoring!... Jim'99