2004 Audi A2 1.4L Diesel · HD04 ECV

The A2's 75bhp 1.4 16v MPI petrol (AWW/AUA/AXP family) is one of the toughest small engines of its era, but Autocar's used guide singles out the coil pack as its recurring fault. Owners on the A2 Owners' Club forum describe exactly the same chase: a cylinder drops out, a diagnostic reads misfire on one cylinder, and a new Bosch coil pack (plus plugs and often leads) clears it. Failure usually shows first when damp gets into the pack area; a neglected misfire will overheat the catalytic converter, turning a £150 fix into a four-figure one.

Autocar names the temperamental dual-mass flywheel as the headline weakness of the 89-90bhp 1.4 TDI (ATL/BHC) engine, alongside a variable-vane turbo that is prone to carbon build-up from UK short-trip use. A2OC members confirm the pattern: a TDi 90 at around 93,000 miles develops a rattle that is a dying DMF, and the correct fix is a Luk clutch-and-flywheel set (the OEM supplier), labour included usually costing more than the car is worth. The earlier 75bhp TDI with fixed flywheel sidesteps this entirely.

The A2 carries its 12V battery in a well under the boot floor. Autocar's used buying guide warns to check for water in the battery compartment caused by tired seals in the rear bumper, and the A2OC's pinned how-to thread identifies the exact culprits: the bumper vents and their flimsy seals, which dislodge after even a light shunt or a bumper replacement, letting water sheet into the bay - members call it the 'fishtank'. Drowned batteries, corroded earth points and tail-light circuit faults follow; the permanent fix is a bumper-off refit with new seals, and repeated partial repairs rarely hold.