Rough engine running and noises when starting or switching off the engine are in some cases too quickly associated with a possible dual-mass flywheel (DMF) defect. Often though the cause of these faults can be found in an unexpected place – in the vehicle electrical system. In this workshop tip we look at this issue and show you that, for instance, dirty ground stubs may be the cause of a fault with the vehicle electrical system.

Corroded contact surface

Cause study

If the contact surfaces are soiled with oxidation or corrosion, the contact resistance of the contacts is increased. This leads to a drop in voltage, which may cause faults with electronic components or cause the vehicle electrical system to fail.

If, for instance, you have a fault with the ignition system, this becomes apparent with noises such as rattling or chattering from the area of the dual-mass flywheel (DMF), the clutch or the transmission. The engine may also take longer to start as a result or the engine may run rough. As part of troubleshooting, the electric contacts should be checked and cleaned where necessary. These contact surfaces are, however, often difficult to access, which makes cleaning more difficult.

Procedure for cleaning the contact surfaces

The cleaning is performed using web rings, which are selected based on the particular surface and size of the contact surface. The set also includes an adapter for cleaning battery contacts.

Note: The pictures used in this workshop tip and the procedure described for cleaning the electric contact surfaces are examples and may vary depending on the vehicle manufacturer and vehicle model.

How-to-guide

Step 1
SACHS cleaning tool
  • Assemble the cleaning tool.
SACHS battery contact cleaner
  • Loosen the battery terminal clamp and remove it from the battery terminal. Observe the vehicle manufacturer specifications.
  • Check the battery terminals for corrosion and soiling.
  • If necessary, clean the battery terminals with the battery contact cleaner.
Battery terminal cleaned
  • Keep cleaned battery terminals dry and free from grease and do not preserve with lubricants.
Clean battery terminal clamp
  • Check the battery terminal clamps for corrosion and soiling.
  • If necessary, clean the battery terminal clamp with the battery contact cleaner.
Battery terminal clamp cleaned
  • Keep cleaned battery terminal clamp dry and free from grease and do not preserve with lubricants.
Clean the electric contact surfaces
  • Loosen screw connections of the electric contact.
  • Check the electric contact surfaces for corrosion, oxidation and soiling.
  • If necessary, clean electric contact surfaces with the appropriate adapter, hook-and-loop pad and web ring.

Note: Use the gray web ring for lighter soiling and coated surfaces (e.g., cable eyes). Use the red web ring for heavier soiling and uncoated surfaces (e.g., grounding point to the body).

Electric contact surface cleaned
  • Keep cleaned electric contact surfaces dry and free from grease.
  • Tighten the screw connections of the electric contact to the tightening torque specified by the vehicle manufacturer.
  • Connect the battery terminals and tighten them to the specified tightening torque. Observe the vehicle manufacturer specifications.

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