Mod Filter


for all your modding needs, recommended by Evilution

Safe Mode

Mod Description
If the car senses that it is getting too much boost, it can panic and put the car into safe mode to protect the engine. So what could cause a car to suddenly create too much boost?
Mod Details
PremiumYes Difficulty Mod ID912 Creditevilution For450 Fortwo451 Fortwo452 Roadster453 Fortwo/Forfour454 Forfour Link Copy to Clipboard

Over Boost

Over boost is when a turbo charged engine creates more boost than expected for the set parameters in the ECU. When this happens, to save the engine from damage, the ECU runs a restricted set of parameters called safe mode.

In safe mode, the wastegate arm is either left wide open so boost pressure cannot be created or the ECU runs restricted RPM, below the level at which the turbo would naturally create boost.

Excessive boost air could damage the pistons, the valves, head gasket, pipes to the engine and the turbo itself. If it didn’t enter safe mode, the car would have to do one of 2 things. Either run the engine lean to reduce power which is no good for the engine, or increase the fueling to keep the ratio correct. Increasing the fueling would increase the power the engine created which in turn would increase the boost even further.

So panicking like a little girl seems to be the best option for the engine.

More often than not, just turning the engine off and on again will reset the fault and allow you to drive properly. The nature of the fault depends how quickly (if at all) the error returns. The fault will either be hardware, sensor or software based although software is rarely the issue unless you have just had the car remapped.


The engine map in the ECU controls the air intake, boost pressure and the fueling. Depending on how you drive, it will use a small set of many available parameters. However, none of the parameters would normally create over-boost.

So if you have just had a remap and the car keeps dropping into safe mode then firstly ensure your air conditioning is off. Turn off all unnecessary electrical items (as long as it’s safe of course, don’t go into full stealth mode at night) and see if it continues to go into safe mode.

Some older (shit) remaps had a problem with the car using too much power which the battery couldn’t keep up with. This created a power shortage (brown out) so the sensors didn’t read correct figures. This fools the ECU into thinking that there is a fault and the car goes into safe mode. Go back to the (shit) remapper and have another remap loaded onto the ECU.

Brown Out – Really?

Yeah, it’s like a black out but not all the power is removed. Brown outs are bad news for electronics. It’s got nothing to do with the little bit of poo that pops out of you when your car suddenly goes into safe mode whilst you are hammering it down the motorway with another vehicle right up your arse.


Well, not so much of the plural. Normally it’s just the 1 sensor that causes the problem. Unsurprisingly enough, it’s the sensor that measures the boost air pressure. The MAP sensor.

The MAP (Mass Absolute/Air Pressure) sensor is a piezo film sensor that deflects when pressurised. The amount of deflection creates a varying voltage which the ECU can use to calculate the air pressure.

It’s not unusual for the MAP sensor to become faulty and either give off an incorrect reading or no reading at all. You can pick up pattern replacements off of eBay for £15. Fitting is 1 bolt and 1 connector. Easy.

There is also the possibility that a faulty AIT (Air Inlet Temperature) sensor could misread the air temperature, causing the engine to run fuel lean or fuel rich. This can lead to detonation which is picked up by the knock sensor. To combat engine dentonation (also called pinking), power is normally reduced by the ECU.

The same result can also occur if the knock sensor is faulty.


OK, now we are down to the engine parts. Normally a bit of a pain to get to, dirty, hot and hard to change. Unfortunately, more often than not, it is one of the following that is causing the issue.


The rest of the information held in this guide is locked to Supporter 6, Supporter 12, Supporter 12+, and Business members of Evilution only.

Use the buttons below to login or find out about becoming a premium member.