Seat Mii
Three-cylinder CNG engine with modified valve seat inserts for CNG operation and 11.5:1 compression ratio. Watch for corrosion on the CNG tank and shortened spark plug replacement intervals in gas mode. Bivalent petrol/CNG operation possible.
Fill up cheaply, drive normally
The Mii with CNG power and 50 kW is an economical choice for high-mileage drivers with access to a gas station. The driving feel matches the regular Mii: functional and dependable. Low running costs are the reason to buy, not driving pleasure.
Engine Weaknesses 4
The CNG pressure tank of the Seat Mii Ecofuel develops rust at the valve connections and gas lines. Missing wax protection is the cause. TÜV refuses inspection. Repair costs exceed vehicle value.
Symptoms: Visible rust on the gas tank, TÜV refusal, tank shutdown by workshop
CNG lines fitted with insufficient torque (recall 24DQ, model year 2018). Nut connections can work loose and lead to gas leaks.
Symptoms: Gas smell, CNG pressure drop, CNG system warning lamp
On the 1.0 CNG CPGA individual gas injectors can fail. A defective injector causes power loss and rough running in CNG mode.
Symptoms: Juddering in CNG mode, power loss, rough engine running, switching to petrol immediately improves running
CNG engines wear spark plugs faster than pure petrol engines. The 60,000 km change interval must be strictly observed, otherwise starting problems and elevated emissions result.
Symptoms: Poor cold-start behaviour, rough idle, elevated consumption
Vehicle Weaknesses 4
Worn steering and wishbone joints cause knocking noises at the front axle. A typical roadworthiness inspection complaint on older vehicles.
Leaks in the refrigerant circuit cause refrigerant loss. Additionally compressor failures and blocked condensate drain hoses are known, causing moisture inside the cabin.
Inadequate underbody corrosion protection leads to rust on the underbody of older vehicles. The exhaust system typically rusts through from the 5th year of operation.
The headlights on the Mii are prone to misalignment and are flagged more frequently at roadworthiness inspections. Defective low-beam headlights are a typical complaint.
Reports & Tests
The Mii passes the roadworthiness inspection without complaints more frequently than the class average, even at higher mileage. Typical weak points are defective rear lights and misaligned low-beam headlights; the exhaust system also attracts attention above average.
