Inside Line: Cambiare


Mercedes C-Class <2014

The Cambiare technical hotline has dealt with issues covering:

Diesel powered cars may experience the engine control unit going into ‘limp home’ mode due to a failure of the differential pressure sensor for the DPF. If no fault codes are recorded in the engine ECU, technicians should check the operation of this sensor as part of their diagnostics.

Technicians diagnosing oil leaks should bear in mind that some C classes have been recalled via VOSA to address a power steering leak at the pump. While the colour of the oil should steer them away from an engine oil leak, old PAS fluid combined with engine grime, may distract them.

Owners have also, reported problems with automatic gearboxes causing the car to feel like the engine is misfiring. Mercedes claim that the gearbox is sealed for life, disregarded this as part of a diagnosis routine.

Problems appear to be few and far between, with cars regularly achieving well over 200,000 miles. High mileage cars could benefit from the automatic transmission oil and filter being changed, as the symptoms may be caused by a slipping/locking torque converter.

Pre-cat lambda sensors make up 21 percent of the top ten Cambiare sales for the C Class. Poor running, hesitation, high fuel consumption and an illuminated EM light could be caused by a faulty pre-cat lambda sensor. These symptoms could also be caused by a split breather hose.

Hard starting and misfires could be caused by mushroom coils (making up 18 percent of Cambiare top sales) or dry coils (11 percent of Cambiare top sales).

High fuel consumption, hard hot-starting and poor performance could be caused by a faulty engine management temperature sensor, (making up 19 percent of Cambiare top sales). Fault codes relating to pre-cat lambda sensors may also be caused by the engine management system reacting to an incorrect signal from this sensor and increasing the fuel delivered by the injectors causing an over rich mixture.

Hard or non-starting, could be attributed to a faulty crank sensor, (12 percent of Cambiare top sales). Loss of power combined with an inability to restart the engine could be the result of an internal breakdown of the crankshaft sensor. Nearly 20,000 models built from Jan 2006 to the end of 2007 were recalled via VOSA to replace crankshaft sensors. Technicians diagnosing similar symptoms should start by looking here.

MAF sensors could be the cause of poor performance or hesitation if the crankcase breather system is functioning normally. (Seven percent of Cambiare top sales). Misfires and hesitation on the 1.8 and 2.0 Kompressor engines, can often be misdiagnosed as a failing mass air flow sensor, as the diagnostic trouble code will be associated with that part. The problem actually lies with ‘unmetered air’ entering the engine. The cause of the problem could be a split crankcase breather hose which sits below the air filter housing hidden from view.

Technicians looking to resolve ‘MAF sensor’ problems should check that there is no unmetered air entering the engine before replacing the sensor.

Brake light switches hold the same ranking as MAF sensors, and providing the bulb is in good condition, technicians should check the operation of the switch next as Cambiare’s technical hotline has taken some calls regarding this issue.

Post-cat lambda sensors take up the remainder of the top ten Cambiare sales at five percent. Fault codes relating to post-cat lambda sensors could be an indication that the catalytic converter is not functioning correctly, rather than failure of the sensor. Technicians should bear this in mind when diagnosing the cause of an illuminated EM light and lambda related fault code.

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