2004 Daihatsu Copen 0.7L Petrol · BN04 BPF

The signature feature of the Copen is its electric hydraulic folding hardtop, but age, weather exposure, and neglected lubrication create troublesome faults. The mechanism relies on an electric hydraulic pump in the boot, four hydraulic rams, and multiple microswitches that report roof and boot lid positions to the roof control ECU. Fluid leaks from aging ram seals, pump motor wear, or misadjusted microswitches cause the roof sequence to stall halfway, leave boot lids unlatched, or fail to operate entirely. Repairs require specialist diagnosis, microswitch realignment, or hydraulic ram rebuilds.

Because the Copen was developed primarily for the Japanese domestic market where winter salt is rarely spread, factory corrosion protection and underbody sealing were inadequate for British winters. Road spray and wet road grit thrown up by the rear wheels pack tightly into the double-skinned rear wheel arch lip and sill seams. Corrosion begins invisibly inside the seams before bursting through as bubbling paint along the top trailing edge of the rear arch, the outer sill seams, and the boot floor edges. Repair requires cutting out rusted inner and outer skin sections and fabricating fresh metal.

The 659cc JB-DET four-cylinder engine is a miniature engineering marvel that revs past 8,000 rpm, but its tiny IHI turbocharger spins at extraordinary rotational speeds. The engine holds only 2.5 litres of motor oil and requires strict 3,000-mile or 6-month oil renewal. When budget-conscious owners stretch servicing intervals, degraded engine oil carbonises in the narrow turbo oil feed banjo pipe, starving the floating journal bearings. This leads to excessive shaft play, compressor wheel rubbing, smoke under boost, and sudden turbocharger destruction.