KTM 125 SX 2024 User Manual

21 TROUBLESHOOTING
128
Faults Possible cause Action
Engine overheats Too little coolant in cooling sys-
tem
– Check the cooling system for leakage.
– Check the coolant level. ( p. 102)
Too little air stream – Switch off engine when stationary.
Radiator fins very dirty – Clean the radiator fins.
Foam formation in cooling sys-
tem
– Drain the coolant. ( p. 102)
– Refill with coolant. ( p. 103)
Damaged cylinder head or
cylinder head gasket
– Check the cylinder head and cylinder
head gasket.
Bent radiator hose – Change the radiator hose.
Thermostat defective –
Check the thermostat.
Guideline
Opening temperature: 70 °C (158 °F)
Malfunction indicator lamp
lights up or flashes
Malfunction in the electronic
fuel injection
– Check the wiring for damage and the
electrical plug-in connections for corro-
sion and damage.
– Read out the fault memory using the
KTM diagnostics tool.
White smoke emission (steam
in exhaust gas)
Damaged cylinder head or
cylinder head gasket
– Check the cylinder head and cylinder
head gasket.
Gear oil exits at the vent hose Too much gear oil added – Check the gear oil level. ( p. 120)
Water in the gear oil Damaged radial shaft seal ring
or water pump
– Check the radial shaft seal ring and the
water pump.

KTM 125 SX 2024 Specifications

General

Displacement	124.8 cm³
Bore x Stroke	54 mm x 54.5 mm
Starter	Electric starter
Transmission	6-speed
Front Suspension	WP XACT-USD, Ø 48 mm
Rear Suspension	WP XACT Monoshock with linkage
Ground Clearance	375 mm
Seat Height	950 mm
Front Tire	80/100-21"
Rear Tire	100/90-19"
Engine Type	Single-cylinder, 2-stroke
Fuel System	Mikuni TMX 38
Front Brake	Disc brake, 260 mm
Rear Brake	Disc brake, 220 mm
Clutch	Wet, multi-disc clutch, Brembo hydraulics
Frame	Central double-cradle type in chrome-molybdenum steel