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Independent Mercedes Specialists


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Mercedes Common Faults​

Check engine light on? Engine running rough?  Here you will find some answers to the most frequently diagnosed Mercedes problems brought into TWG.  We do not recommend you assume that the answer here directly relates to your car.  Accurate diagnosis of a problem typically saves you money.  And, you should know that often third parties will misdiagnose a car for what appears to be similar problems or related diagnostic codes. Also ever heard the saying “a little knowledge is dangerous” its true! to much Googling can cost you extra money if you assume your problems are related. Here are some common issues we have experienced at TWG Sport.

Gearbox problems

If your transmission is stuck in gear and your gearbox check light is on

1.    Pull over and turn the car off. Remove the key.

2.    Do not press the Throttle pedal or any other buttons on the car.

3.    Wait 20 seconds.

4.    Start the car and drive to see if it is out of limp mode the gearbox check light may be still on.

Your transmission may be back to normal but there may be underlying issues that you need to address. If you ignore them, the car will start going into the limp mode more frequently. Don’t forget that first warning! You need to find the reason your transmission is going into limp mode or not shifting..

The 5-speed transmission that was used between 1995 up to 2008 can have some common issues including oil leaking from gearbox pan electrical plug seal. Therefore any signs or issues you should check your gearbox oil a workshop dipstick may be required.

If your problem repeats the gearbox may require a new valve block including electrical switchboard.

The vehicle must be connected to a Mercedes Star Diagnosis to confirm any issues.

Engine has poor performance at high rev range

The air mass meter could be at fault, an air mass meter is also referred to as a mass air flow sensor (MAF). An air mass is essentially a device meant to measure the flow of air into the engine. This sensor is required for the engine control unit (ECU) to balance as well as deliver the accurate fuel to the engine. Inside the sensor is a wire coil that’s heated up to a constant temperature once air is passed by the wire it changes the resistance od the current supplied to the engine control unit. Overtime the wire coil gets contaminated giving the wrong reading resulting in poor performance and rough idle. An old trick of the trade is to unplug the MAF and see if the performance improves because this will direct the engine into limp home giving a default fuel supply. The vehicle must be connected to a Mercedes Star Diagnosis to confirm any issues.

Mercedes SBC warning Service due

The Sensotronic Brake Control (SBC) ABS Pump has a service life (also known as a life expectancy) programmed into the control module which works off the number of brake actuations and time. Once this time limit has been reached, the Sensotronic Brake Control (SBC) light may illuminate on the dash or a brake related warning may appear on the trip computer. Once this happens, the Sensotronic Brake Control (SBC) system is de-activated and the hydraulic braking function mode is activated. Safety Note when changing brake components on the SBC system the brake pump is live and must be put into sleep mode before any work is carried out.

When the Sensotronic Brake Control (SBC) ABS pump fails the best option is to replace the unit with new but there are reconditioned units available once fitted require re-programing.

V6 Diesel Engine warning light on poor performance

The vehicle must be connected to a Mercedes Star Diagnosis to confirm any issues.

Any turbo related Engine fault codes-Read Often the assumption is made that the turbo is at fault. This can cause unnecessary maintenance to be performed. In many cases the cause is an oil leak directed onto the turbo actuator valve fitted underneath the manifold, the manifold leaks oil through the gaps in the swirl flaps the remedy is to replace the manifold and the actuator not the Turbo.

Mercedes Timing Chains

The Mercedes Petrol and Diesel  engines are  fitted with single row chains are prone to excessive timing chain wear and premature failure. Rattling noise from the front of the engine is indicative of the condition. Timing chain failure may call for engine rebuild.  The issue applies to all applications and power variants of the engine produced from 01.01.2003 to 01.03.2011. The most seriously affected units which require the most extensive repairs were produced from 01.01.2007 to 01.01.2011.

Any rattles turn of the engine and recover to TWG we have seen many of these engine’s survive just with a replacement chain kit price about £1500 not 4k to 5k! what other garages may charge.

Mercedes Blocked DPF


The electronic indicator lights, the vehicle has no more power and extremely high fuel consumption? The diesel particulate filter has only a limited capacity to store particulates. From a certain amount of soot, the soot particles must be burned in a regeneration process to CO2 and ashes. Different reasons can mean the regeneration process does not start and in consequence the DPF gets clogged with soot particles.

Possible causes:

  • Defective or not fully functioning injectors
  • Sooty or coked EGR valve
  • Different qualities of fuel or Bio fuels
  • Short distance driving profile


Particulate filters can be cleaned in an installed condition, rapidly, simply and significantly more economically than replacing them.

  • Used when regeneration is no longer possible
  • Cleaning to almost new condition possible
  • No expensive new installation
  • Cleaning without disassembly of the particulate filter
  • Non-flammable
  • Neutral ash and metal-free formulation
  • Evaporates completely

Compatible with other materials

An overloaded DPF: That is expensive.

For replacement of the part customers have to pay a lot of money. For a new diesel particulate filter between £600 and £4000 would be charged. In addition a prolonged stay in the workshop and a rental car has to be organised. TWG Solution: Cleaning instead of replacement.