BMW Engine Malfunction Reduced Power

BMW Engine Malfunction Reduced Power Problem

BMW Engine Malfunction Reduced Power is a common problem among many BMW models including 335i, 535i, 745i, X1, X3, X5.  In this guide, you will learn about common problems that cause BMW engine malfunction and how to diagnose the problem yourself.

BMW Engine Malfunction Reduced Power message comes on when the engine computer (DME module) in your car detects a problem. When the BMW engine malfunction message pops up on your iDrive the check engine light (service engine soon) will also come on. The color of the check engine light can help you get an idea of how serious the problem is. 

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Symptoms

In addition to typical BMW Engine Malfunction message on the iDrive screen, BMW owners may notice the following symptoms as well. 

  • Reduced Engine Power
  • Increased emissions
  • Reduced Output
  • Transmission in limp home mode ( in some cases)
  • Drivetrain malfunction and engine light
  • Reduced engine message coming up during acceleration

Common Causes

Here is a list of common problems that cause BMW Engine Malfunction Reduced Power message. 

Valvetronic

Most BMW engines are equipped with Valvetronic. It variates the amount of intake valve lift, eliminating the need for a throttle plate. Although this is a quite complex system, it is quite durable. If it fails, you might have poor throttle response and lack of power. Usual failure points are an electric motor and an eccentric shaft position sensor.
Codes: 2A61, 2A63, 2A67, 2A6F, 2A70

 

Vanos

Vanos is operated by oil-powered actuators. It is a very simple and robust system. In most cases, it will fail if there is an oil sludge buildup within the vanos solenoids. This is a result of too long oil change intervals. Luckily, faulty Vanos solenoids are an easy and cheap thing to fix.  In addition to the "BMW engine malfunction reduced power" message you will also notice engine noise such as tapping or knocking noises (VANOS area). Usually after starting a cold engine or at idle for the first few seconds.
Codes: 2A82, 2A87

bmw engine malfunction reduced power x6 due to vanos

Oxygen Sensor

BMW engine control uses readings from upstream O2 sensors to achieve optimal engine performance. Upstream O2 sensors can get fouled by excessive fuel or oil consumption. Furthermore, a damaged wiring or a loose connector is also possible. Whatever the reason, it will affect the engine performance, and you will get a yellow 1/2 'check engine' light.
Codes: 2C9C, 2C9C or P0171 to P0174

BMW oxygen sensor engine malfunction sign

Ignition Coils

Ignition coils can fail from a number of reasons. It will result in a misfire, causing the engine to shake and judder under acceleration. Misfire is very damaging to your catalytic converter, so don't drive your BMW with a misfire. Ignition coils are easy to replace, so it's a good idea to have one spare ignition coil. A loose connector to the ignition coil can cause  BMW engine malfunction yellow light to come on. 
Codes: P0300 to P0306

bmw engine malfunction yellow light due to loose ignition coil

Timing Chain

Timing chain-related problems can trigger a 'check engine' light. Although timing chains are supposed be a life-long item, they can get exclusively stretched with time. Tensioner or plastic guides can fail, too. Timing that has jumped two or three teeth will cause engine rattle, a yellow 1/2 'check engine' light and Vanos related codes. Red 1/2 'check engine' light will indicate a bigger timing jump. In either case, turn off the engine immediately and do not restart it. 

bmw engine malfunction reduced power 535i

Battery

A weak battery can cause BMW Engine Malfunction Reduced Power message on the iDrive screen. BMW are very senstive to the voltage and if the battery is old, it may hold a proper charge. If your battery is over 7 years old it is time to change it to avoid other electrical issues. A bad alternator regulator can cause similar symptoms as well. 

bmw engine malfunction reduced power m3

Guide: How to replace BMW battery. 

High-Pressure Fuel Pump (HPFP)

Newer bimmers, starting from E90 335i, have engines with high-pressure fuel injection. This is a delicate system which can be damaged by a low-quality fuel.  High-pressure fuel pump and injectors are the usual failure points. Symptoms include engine hard starting with long cranking, rough idle and a yellow 1/2 'check engine' light. In most cases, power output and acceleration are heavily affected. You must check and replace the faulty pump or injectors as soon as possible.
Codes: 2FBA, 2FBF, 29DC, 29E2

Turbo

If you have a turbocharged BMW that feels down and power and sluggish on acceleration, it is highly possible that you have a boost leak.  This can be caused by something simple as a broken vacuum line. Boost solenoids that operate the turbochargers can fail. You should also check the charge piping that connects the turbo with intercooler and intake manifold. These are rubber hoses that can break or simply slip off. Lastly, a stuck open wastegate or a leaking blow-off valve will also cause low boost issues.
Codes: 30FF for a boost leak

How to diagnose BMW Engine Malfunction Reduced Power

BMW cars are very complex and precise piece of engineering. A generic OBD2 reader just won't do the trick.

Scanner used: TopDon ArtiDiag 

Alternatives: Foxwell for BMW , Carly for BMW

To diagnose BMW Engine Malfunction you will need a BMW Specific Scanner that is able to read manufacturer specific fault codes. Pay attention to fault codes from the DME module and also perform a full system scan. 

BMW Engine Malfunction Light Meaning

The classic yellow 'check engine' light will be on when there is a problem with the engine or emission control system. In most cases, this will not affect engine operation. You shouldn't experience any lack of power and changes driveability. Have in mind that models for the US market usually have 'Service engine soon' light instead. If there are no other symptoms, you can safely use your BMW until you have a chance to fix the problem.
Half Yellow 1/2 'check engine' light indicates an engine related problem that will affect the power output. It comes with 'Engine fault! Reduced power' message on your iDrive display. It can be caused by the failure of various sensors or solenoids. The engine ECU will cut down the power output to protect the engine. You might also have some driveability issues. Yet, even with this fault, your BMW will still get you home. Drive moderately and don't push the engine. Avoid unnecessary driving until you have fixed the problem.
Red 'check engine' light indicated a serious issue. It means that something is seriously wrong with your engine. If you get this type of 'check engine' light, there is only one correct course of action. Stop the car, turn off the engine and call a tow truck. Don't be tempted in restarting your BMW to see if the fault will go away. This can easily destroy the engine.

Frequently Asked Questions

My BMW has a big yellow check light and says 'Engine fault! Reduced power'. What should I do?

If you have this warning, it means there is a serious problem with your engine. It is still OK to drive to your destination, but you should adjust your driving style to 'moderate'.  A good idea is to pull over at a safe place and take a look under the hood. Fix the problem as soon as possible. This message can come up on an E60 E70 E90 E92 E65 F10 etc. 

What does 'drive moderately' really mean?

As the engine is not operating perfectly, you should not put it under hard load. Avoid harsh accelerations and high engine speeds. Drive gently. Additionally, pay attention to any signs of abnormal operation. Unusual exhaust smoke, engine judder or high engine temperatures are causes for concern. 

My BMW has a 'check engine' light, but I can't read any fault codes?

Some OBD2 readers are capable of reading only the mandatory powertrain codes (Pxxxx). As BMW is more complex than most cars, it has many  manufacturer specific codes.  For a good engine insight, you will need a scan tool capable of reading this kind of codes.

Additional Resources

  1. N55 Engine Failsafe - FC 120308
    Boost Pressure Control, Plausibility:  Pressure Too Low Stored in DME Fault Memory 
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