Mercedes W205 C180 Engine Vibration and Ignition Faults

The engine fault light is often illuminated in vehicles with advanced engine technology such as the Mercedes-Benz W205 C180. This indicates that there may be a mechanical or electronic issue. A motor that starts to run rough, misfires in the cylinders and error codes P0354/P0300/P0304 on the OBD device are all signs of a serious situation.

Definition of Fault Codes

P035413 – Ignition Coil A Circuit Open Circuit (4th cylinder)

This code indicates that there is a continuous interruption or loss of signal in the coil circuit attached to cylinder 4. This is caused by:

• Contact in the coil socket is poor
• The wiring harness has a break or short circuit
• The ECU is unable to send the signal to coil

P030085: Random Cylinder Ignition Fault

This code indicates that there is an irregular firing of multiple cylinders. Causes:

• Fuel system pressure fluctuations
• Spark plugs, coils or injectors can cause problems
• Combustion chamber problems such as vacuum leaks or compression loss

P030485 – Continuous Ignition Failure in Cylinder 4

This code points directly to the cylinder number 4. This code indicates that the coil and spark plug have been replaced.

• Injector failure
• Wear on piston rings and valves
• Fuel distribution problems

Interventions Performed

• 4 spark plugs replaced
• Renewing 4th cylinder coil
• The fault was cleared, but it recurred

There are other points to be checked

Part/System	Explanation
Coil sockets and cables	Does the new coil receive a correct signal? The cable ends may have been damaged or loosening.
Fuel injector (4th cylinder)	The cylinder won’t fire if the injector is blocked, or if it doesn’t spray. You should check it with a testing device.
Test of cylinder compression	There may be an internal mechanical issue in the fourth cylinder, e.g. Even if the ignition is on, combustion may still not take place if there are valve leaks.
Fuel system changes: Recent updates	There may be a problem with the connection. It is possible that the pressure sensor has malfunctioned.

What should be done?

• It is important to read the fault codes again and record them.
• OBD Live Data should be used to check the injection and ignition timing for the 4th cylinder.
• A cable tester should be used to measure the coil socket and wiring harness.
• To see if it helps, swap the injector from the 4th to another cylinder.
• It is important to perform a compression test. If the compression is low, mechanical interventions are required.
• Check the ECU software. In rare instances, software-based errors can occur.

The cause of engine vibration can be more than just a component failure. It may also be the result of the interaction between multiple systems. A problem in a sensitive engine like the Mercedes W205 can cascade to affect other components. Therefore:

• Replace parts only if the fault code is present.
• The system should be analysed holistically, and backed up by live data.

Replacing just one part may not be enough

In most cases, ignition problems (P0300-P0354) on C180 W205 engines can be resolved by changing the coil or sparkplug. If the problem persists this is not enough. This is especially true if the problem persists on the same cylinder.

• Injector test
• Electrical system inspection
• Test of cylinder compression

The rules must be followed without exception.