Engine Codes First Inspection

Joseph Technical Support Specialist Commack, New York Posted   Latest   Edited  
Tech Tip
Driveability
2014 Mercedes-Benz C350 3.5L (M 276) 7-spd
Ghost Codes

This is just something as a preliminary check as ive come across this a couple of times already. 

When diagnosing engine codes or symptoms, take a look at the engine control module first. More specifically, at the contact pins

There may be oil present at the pins both on the engine control module side and the wiring harness side. This can lead to malfunctions. If this is something you have, strongly consider stopping here and fixing this before moving on to diagnosing codes and symptoms. You may be wasting time unless its an obvious issue like a ripped out wire or broken component. Generally , if you find oil at engine control module, it is coming from the camshaft adjustment solenoids on the front covers. Check the following :

O2 sensors 

Camshaft hall sensors 

Injectors

Thermostat 

Those are the commonly affected components 

Any and all contaminated components require replacement including the engine control module and the engine wiring harness 

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Dmitriy Analyst
Toronto, Ontario
Dmitriy
 

There is a school of diagnostic thought that promotes non-invasive methods first, as disturbing the wiring and connectors may temporarily fix the problem and make further progress impossible or inconclusive. This is even more of concern when diagnosing intermittent issues. With this in mind, under what conditions (e.g., combination of codes and observed failures) would you still recommend

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Julio Owner/Technician
Laurel, Maryland
Julio
 

Excellent point Dmitriy. In my opionin it would greatly depend on the vehicle and if this is a known issue. On certain Mercedes and BMWs with certain codes, I immediately check for this as they are known issues.

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