Engine power reduced


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What does the message “engine power reduced” mean?

In modern vehicles, the info message “engine power reduced” is a common problem, because newer vehicles have many sensors installed, in and on the engine. These usually have the task of measuring something and forwarding these measured values to the engine control unit. The engine control unit has to take various decisions, such as adjusting the injection quantity or the ignition.

In case there is an issue, the engine control unit may also calculate from faulty data transmitted by the sensors.

As a result, an error is stored in the error memory and the engine control lamp may light up. If the error is serious and can lead to damage to the engine, the engine control unit switches to a so-called emergency program or limp mode. In this emergency program, the power of the engine is usually reduced in order to protect the engine from further serious damage, as already mentioned.

Understanding the engine power reduced warning light

Engine power reduced

There is no specific warning lamp for a scenario when the engine power is reduced. However, if the engine control unit is in emergency operation mode, the check engine light turns up.

In most cases, vehicles with a multimedia system will also display a flashing error message that gives the driver a more detailed description of the error.

Troubleshooting of common causes when engine power reduced

This cannot be answered in general, because all possible errors can be responsible for the engine control unit deciding to switch to the emergency program or limp mode. But in general, it can be said that as soon as the engine control unit detects that an error is stored that could damage the engine, there is a reduced power warning.

Here you can see some examples of faults and systems that can lead to reduced engine performance:

Diesel particulate filter:

Since the diesel particulate filter is responsible for exhaust gas after-treatment, this is a very sensitive system that is also very strictly monitored by the engine control unit due to legal regulations.

If the engine control unit detects an error about the DPF, such as “diesel particulate filter heavily loaded” or “exhaust gas temperature sensor signal implausible”, an error is immediately stored inside the error memory and the car switches to emergency mode.

Exhaust gas recirculation:

Similar to the diesel particulate filter, the so-called “EGR system” is also responsible for exhaust gas after treatment. Therefore, the EGR is also subject to legal regulations. It is
often the case that the EGR valve is stuck or can no longer be adjusted as desired. As soon as the engine control unit notices that the measured values no longer match the target values, an error is stored and the emergency program is activated.


In the case of the turbocharger or the turbo system, the situation with reduced engine performance is somewhat different. If the turbocharger no longer works properly or if there is a leak in the system, the engine power is generally lower without the intervention of the engine control unit. This is related to the function of the turbocharger because it is used to achieve higher engine performance.

So if the turbocharger fails, there is power reduced due to the failure of the turbocharger.
But of course, it is also possible that only the boost pressure sensor, for example, is delivering a false signal. To prevent too much boost pressure from being generated in the charge air system, the engine control unit may reduce the engine output.

Glowing system:

A fault in the glow system or glow plugs does not directly lead to reduced engine performance. This is because the main task of the glow plug is to preheat the combustion chamber of a diesel engine to enable combustion. However, since the demands placed on the glow plugs in modern vehicles are becoming ever higher, the glow plugs continue to operate even while the engine is running, for example, to enable regeneration of the diesel particulate filter.
For this reason, a fault in the glow system usually results in consequential faults in the diesel particulate filter, which can lead to low engine power.

Catalytic converter:

As with the turbocharger, the catalytic converter itself can also lead to low engine performance. This is because if the catalytic converter comes loose from its metal housing and thus obstructs the flow of exhaust gas, lower engine performance can also be observed. In this case, the exhaust back pressure is too high. Often, no engine control lamp lights up in this case.

But also here, the lambda sensor can lead to reduced engine power.

Keep in mind, that every car has different software and modules built-in. Therefore specific features will vary with every model.

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