It has been noted that brake light switches have been the highest selling replacement parts among Cambiare’s top 10 sales for the E class. Technicians should check this ‘weak point’ in the system after they have checked for failed bulbs. A failing brake light switch may also be caused by cutting out and cruise control problems.
Crank sensors, the second highest selling engine electrical item, generally bring up a P0335 fault code on a code reader. Failure to start from hot or cold may be the result of a failing Crank sensor.
Poor hot or cold starting and/or poor running/high fuel consumption could also be caused by a faulty Engine Management Temperature Sensor, the third top seller. Failure of this sensor will cause the ECU to supply an incorrect signal to the fuel system, by inaccurately reading the engine temperature. This will cause the engine to run either too rich or too lean. It is advisable to read live data from the sensor and compare this reading to an actual temperature measurement, taken with a thermometer.
Misfires, poor running/starting could be the result of a failing camshaft sensor, the next in the top selling list. Technicians looking for a failing camshaft sensor will generally notice Diagnostic Trouble Code P0340. It must however be borne in mind that fault codes refer to the circuit involved and not just a single component. The fault may lie in a poor connection or broken wire, as much as a failed component.
Misfires could also be the result of a failing Mushroom coil. In case an oscilloscope is not readily available, the specific faulty coil can be located by swapping a coil from one cylinder to another to see if the misfire follows it. It is also recommended to replace all the coils at the same time as the failed one to maintain ignition performance. This will also prevent the possibility of a similar failure soon after, as the other coils will have done as much work as the failed one.
ABS sensors also have a place in the top 10 selling Cambiare parts for the E Class. A failed/failing ABS sensor will generally illuminate the ABS warning light on the dashboard, warning the driver that there is a potential problem with the circuit, and that the ABS system may not function correctly under heavy braking. Technicians are advised to carry out a continuity check of the ABS circuit along with a component test, as part of their diagnosis, before replacing the ABS sensor. It should also be borne in mind that once the sensor is replaced, the fault code gets removed only after the vehicle has been driven for some time, as the system has to notice a functioning sensor before it allows the code to be cleared. ABS faults are frequently ‘created’ in the workshop following wheel bearing replacement, as the sensor gets easily damaged if not removed as part of the bearing replacement or the bearing is fitted the wrong way around.