The engine is attached to the rest of the car via rubber engine mounts. As rubber is an electrical insulator, a separate earth strap is provided between the engine block and the car chassis to maintain electrical earth continuity.

The earth strap provided on all fortwos between 1998 and 2005 was a copper braid. This is fairly common on many other cars, not just smarts. However, over time, the copper begins to corrode and break down. Spurious engine electrical faults can be attributed to poor engine earthing.

There are a number of third party engine earth straps available from eBay and other online shops. In our opinion, these should be avoided as we have observed a number of cases where these straps have failed after a short period of time. Analysis of their fabrication has revealed factors such as poor crimping and low quality ring-crimps have contributed to failure. Others have been made from cables which are too stiff and are not forgiving enough to respond to the natural movement of the engine.

Smart's latest version of the engine strap includes a multistranded core (for flexibility) and insulated sheath. These cables retail at just under £6 from smart making them an obvious choice if your strap needs replacing.

Engine earth strap part number: Q000 3105 V005 0000 00

To replace the strap, you either need to raise the car or remove the rear panels. In the following picture, we noticed that a harsh winter and road salt had badly corroded the earth strap which was breaking up to the touch.

The old strap is held in place with an E10 bolt where it attached to the engine (gearbox bell housing).

The other end secures to the tridion just by the top intercooler.

Use a 10mm hex socket to remove it from the mounting stud.

Compare the old strap with the new one. For the new strap, the angled ring-crimp attaches to the tridion. The straight ring-crimp (by the label) attaches to the engine block.

Ensure that both ends of the strap are fully secured before starting the car.