Daihatsu Boon: common faults & what to check

Which Daihatsu Boon are you looking at?

2 generation variants documented. Pick the shape you recognise: the faults, the servicing and the timeline below all narrow to it. Free, no account needed.

Engine not documented

2 variants documented

2000–2005M1002000–2005M100Engine not documented for this generationEngine not documentedDocumented issues5 knownSee faults & what to checkPhoto: order_242 from Chile via Wikimedia Commons, CC BY-SA 2.0.

2005–2015M3002005–2015M300Engine not documented for this generationEngine not documentedDocumented issues8 knownSee faults & what to checkPhoto: Tokumeigakarinoaoshima via Wikimedia Commons, CC BY-SA 4.0.

Now narrow it to the engine

A 1.8 and a 2.4 of the same car do not fail the same way, so the faults below narrow to the engine as well as the year. Free, no account needed.

Start your free check on this Daihatsu Boon

No plate needed. You get the risk score, the buyer's checklist and the guided inspection for the exact car you picked above — not the whole nameplate.

The checks worth doing on a Daihatsu Boon before you hand over any money. Every documented fault is listed below, each with its own page.

• Serious issue

  Establish timing belt replacement history before purchase — if unknown, treat as overdue and factor replacement into the purchase price.

  See why

  EJ-DE and K3-VE Timing Belt Failure (Interference Engine — Engine Destruction Risk)

  Both M101 (EJ-DE 1.0L) and M300 (K3-VE 1.3L) Sirion engines use rubber timing belts in interference configurations. If the belt snaps, pistons contact valves causing catastrophic and irreparable engine damage. The EJ-DE has documented failures at lower mileages than expected when service history is absent. Belt replacement is due every 90,000 km or 6 years. The majority of imported Sirions arrive in NZ/AU with no documented belt history. This is the highest-risk pre-purchase check on any Sirion.

  What you would notice

  • Sudden engine stoppage while driving with no warning (belt snapped)
  • Engine cranks but does not fire (belt skipped or broken)
  • Ticking or slapping from the timing belt area before failure
  • Total loss of compression across all cylinders after belt failure

  Typically $600–$8,000 to put right.

• Serious issue

  Cold-start the engine and listen for chain rattle before oil pressure builds.

  See why

  K3-VE Timing Chain Stretch and Guide Failure

  The M300 Sirion shares the K3-VE 1.3L engine with the Terios J102 and inherits the same chain-guide cracking and chain-stretch fault. Oil sludge buildup accelerated by infrequent servicing destroys the tensioner hydraulics, allowing the chain to jump a tooth and cause severe valve-to-piston contact in the worst cases. Lower-mileage M300 units that have been well-serviced are generally unaffected.

  What you would notice

  • Rattling from the top front of the engine on cold start
  • Misfires and rough running at idle or under acceleration
  • Camshaft position sensor fault codes (P0016/P0017)
  • Engine oil with a dark, gritty appearance

  Typically $900–$2,400 to put right.

• Serious issue

  Check the coolant reservoir for oil contamination or brown scum.

  See why

  EJ-DE Head Gasket Failure Following Overheating

  The EJ-DE 1.0L three-cylinder aluminium engine in the M100 Sirion is intolerant of overheating. The cylinder head warps at relatively low overheat temperatures, allowing combustion gases to enter the coolant circuit. This is worsened by the small coolant capacity and the plastic coolant reservoir cap which fails to hold pressure when aged, allowing the system to boil at lower temperatures. Many M100 units in the NZ used market have a history of at least one overheating event.

  What you would notice

  • White smoke from the exhaust particularly on startup or under load
  • Coolant loss without visible external leak
  • Bubbling in the coolant overflow reservoir
  • Milky or foamy residue under the oil filler cap

  Typically $800–$2,200 to put right.

• Costly issue

  Run a finger along the bottom hem of each door — bubbling paint indicates trapped moisture and rust behind the hem.

  See why

  Rear Sill and Door Bottom Edge Corrosion

  M100 and M300 Sirion bodies corrode predictably at the rear sill ends where road water is thrown by the rear tyres, and along the bottom edges of all four doors where the hemmed seam traps moisture. The rear quarter panel above the rear wheel arch also blisters. NZ-imported M300 units often show this rust pattern earlier than Australian-delivered vehicles owing to higher rainfall and coastal salt exposure. Rust in the door bottoms is largely cosmetic but untreated sill rot can spread to the structural floor pan.

  What you would notice

  • Paint bubbling along the bottom edges of doors
  • Rust staining or perforation on the rear sill ends behind the rear wheels
  • Blistering paint on the rear quarter panels above the wheel arch
  • Water ingress on interior carpet near the sills

  Typically $400–$2,500 to put right.

• Costly issue

  Test drive in light traffic with gentle throttle in the 20–60 km/h range.

  See why

  CVT Shudder and Clutch Pack Wear

  M300 Sirion models equipped with the Jatco CVT are prone to low-speed shudder documented consistently across Sirion owners in NZ and Australia. CVT fluid degradation over time breaks down the steel-belt friction material. Neglected services — fluid changes are due every 40,000 km — significantly accelerate wear. Full CVT replacement requires sourcing units from Japan, making repairs expensive.

  What you would notice

  • Vibration or shudder at 20–60 km/h under light acceleration
  • Lurching when pulling away from rest
  • CVT warning light or transmission slipping at highway speeds
  • Dark brown or burnt-smelling CVT fluid

  Typically $250–$4,500 to put right.

• Costly issue

  Remove oil filler cap and inspect interior for thick dark sludge or varnish coating.

  See why

  K3-VE2 VVT-i Actuator Sludge Blockage

  The K3-VE2 engine in the M300 Sirion incorporates Toyota-sourced VVT-i (Variable Valve Timing with intelligence) on the intake camshaft. The VVT-i actuator is an oil-pressure-driven phaser mounted on the cam sprocket that advances or retards valve timing. The oil galleries feeding the actuator are very fine-bore (approximately 1.5 mm). When engine oil service intervals exceed 7,500 km or low-quality oil is used, thermal degradation of the oil produces carbon and varnish deposits that partially block these galleries. Reduced oil pressure to the actuator causes it to stick in the retarded position or oscillate erratically. The M300 Sirion is frequently serviced at long intervals due to owners treating it as a disposable city car, making sludge-related VVT failure the most common engine complaint on this generation.

  What you would notice

  • Loud rattling or chain-like noise on cold start lasting 3–10 seconds
  • Rough idle and hesitation when engine is cold
  • Check engine light with VVT-i or camshaft position fault codes (P0011, P0014)
  • Reduced fuel economy and sluggish low-rpm response
  • Oil pressure warning light in severe sludge cases

  Typically $400–$2,200 to put right.

Daihatsu Boon service schedule

What falls due, and at what distance, for each generation of the Daihatsu Boon. These are the model’s intervals — the car’s own service book is the only thing that can tell you what has actually been done to it.

What these repairs cost on other cars

Some of the Daihatsu Boon’s documented faults are repairs other models share. Each page lists the documented NZ cost for every model it affects.

• Cambelt Replacement Cost
• Timing Chain Replacement Cost
• CVT Gearbox Repair Cost
• Head Gasket Repair Cost

Other Daihatsu models