Cause
Heavy keyring wearing the ignition barrel
A heavy keyring wearing the ignition barrel and its switch. The weight hangs on the key all the time the vehicle is running, and over years it wears the barrel's tumblers and loads the switch behind it.
The symptoms are intermittent and follow movement: the engine cuts out over a bump, accessories drop out, or the key turns with unusual slop. A vehicle that stalls when the keys are knocked is describing this, and it was behind a very large safety recall for exactly that reason. It also wears the transponder's coupling, producing immobiliser faults on a key that reads fine when held still. Ask the owner to try a single key with nothing on the ring — a free test that separates barrel wear from an electrical fault.
Typically an easy fix. Often worth checking before paying anyone to look.
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Codes where this is a likely explanation first, rather than merely a possible one.
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