IsItAGoodCar
Reliability Guide

Common Problems with the
2003 Daihatsu Copen

The Copen debuted in the UK featuring an aluminium electric hydraulic folding hardtop and a high-revving 659cc JB-DET four-cylinder turbocharged engine producing 68bhp.

What changed for 2003

  • •UK market launch with right-hand drive, Active Top electric folding roof, and 659cc JB-DET turbo engine
  • •Standard specification including heated leather seats, 15-inch alloy wheels, and Momo leather steering wheel

Common MOT watch-outs

  • !Rear wheel arch seam and sill corrosion from British winter road salt
  • !Excessive emissions or smoke caused by turbocharger seal wear on neglected engines
4
Known Issues
2
Serious
1
Moderate
1
Minor

All Known Issues

Rear Wheel Arch Trailing Edge and Sill Seam Corrosion

SeriousBodywork & Rust

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.

Est. Repair Cost: £550–£1,500
Warning Signs:

Paint blistering and bubbling along the rear wheel arch lips, especially near the rear bumper junction, Brown rust staining visible along the inner sill seams when opening the doors, MOT inspection failure for corrosion within prescribed structural areas of the body shell

What to Inspect:
  • Feel behind the inner return lip of both rear wheel arches for packed damp silt and flaking metal
  • Inspect underneath the car along the sill jacking points with a bright inspection torch
  • Lift the boot floor carpets to examine the seams around the rear suspension turrets and spare wheel well
Verified by IsItAGoodCar Research TeamUpdated

Turbocharger Bearing Wear and Oil Starvation (0.66L JB-DET)

SeriousEngine

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.

Est. Repair Cost: £700–£1,300
Warning Signs:

Noticeable puff of blue oil smoke from the dual exhaust tailpipes upon initial acceleration or boost build-up, High-pitched siren whine or scraping metallic sound when accelerating through the turbo boost threshold, Loss of acceleration power accompanied by oil pooling in the intercooler pipework

What to Inspect:
  • Scrutinise the service documentation for unambiguous proof of frequent oil changes every 3,000 miles
  • Remove the air intake pipe to check the turbocharger compressor shaft for radial and axial play
  • Check the exhaust tailpipes for greasy oily residue rather than a light dry carbon haze
Verified by IsItAGoodCar Research TeamUpdated

Active Top Hydraulic Folding Roof Mechanism and Sensor Failure

ModerateBodywork & Rust

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.

Est. Repair Cost: £350–£1,100
Warning Signs:

The folding roof pauses midway through the retracting or closing cycle and refuses to move, Continuous roof warning buzzer sounding while driving despite roof appearing latched, Hydraulic fluid residue staining the boot carpet near the pump and reservoir assembly

What to Inspect:
  • Operate the roof through several complete cycles with the engine idling, timing the sequence to ensure it takes approximately 20 seconds
  • Verify that the boot divider pull-screen is seated firmly in its safety interlock microswitch clip
  • Inspect the hydraulic fluid reservoir in the boot compartment for correct oil level and clarity
Verified by IsItAGoodCar Research TeamUpdated

Exhaust Mid-Pipe Baffle Weld Cracking and Silencer Corrosion

MinorExhaust & Emissions

The original factory exhaust on the Copen is built from mild steel with chrome tips. A well-known structural weakness occurs just behind the driver's door, where the pipe connects to the centre baffle box; vibration and heat cycling cause the weld to crack and blow. In addition, the twin chrome exhaust tailpipe trims tend to corrode and fall off. Because genuine Daihatsu replacement exhaust sections are scarce and costly, most UK owners fit a bespoke aftermarket stainless steel exhaust system.

Est. Repair Cost: £150–£380
Warning Signs:

Blowing or buzzing exhaust note resonating directly below the driver's seat during acceleration, Missing or severely rusted chrome exhaust tips on the rear silencer outlets, Faint exhaust smell entering the cabin when stopped with the roof lowered

What to Inspect:
  • Look underneath the car just behind the driver's door to inspect the baffle weld joint for black soot blow-by
  • Check whether an aftermarket stainless steel exhaust system has already been installed by a previous keeper
  • Gently wiggle the rear exhaust tips when cold to ensure internal silencer baffles are not rusted loose
Verified by IsItAGoodCar Research TeamUpdated

Buying Tips for 2003 Daihatsu Copen

  • Verify that the previous owner ran the car on high-octane 97/98 RON fuel to prevent knock-sensor timing pull
  • Inspect the turbo oil feed and return pipes for baked oil residues and exterior weeping
2004–2005
Check a 2003 Daihatsu Copen by Registration