Troubleshooting Tips

From DucatiWiki

Troubleshooting table for various components on the 02-03 ST4s

This assumes that you are working with a machine that is familiar to you and has been working well up to this point. All general maintenance has been kept up to date. (dharhay)

Component	Location	Symptom	Remedy
TPS	Horiz cyl throttle body	High idle rpm at rest	Shaft rust prevents full retract of butterfly, clean and reassemble
H2O Temp Sensor - Instrument	LH engine Vert. Cyl. just above & to left of engine mount	Erratic temp reading	Replace
H2O Temp Sensor - Control	LH engine Horiz. Cyl. just above coolant hose	Poor running due to excess fuel	Replace
Oil Pressure Sending Unit	RH engine side case near dipstick	Oil light comes on	Check and replace
Ambient Air Temperature Sensor	Under front fairing on LH side	No known cases of malfunction	N/A
Engine Crank Position Sensor	LH engine side case behind coolant hose	Erratic tach, wont run	Check resistance of sensor, if high replace. Chg gap to .1mm
Starter Relay 1	RH engine in front of battery box	Does not engage	Replace
		Does not disengage	Remove power, Replace
Fuel pump/ Coil/ Injector Relay	Under seat	Fuel pump not on/ No spark/ No injector/ erratic behavior	Replace
Main (ECU/ display) Relay	Under front fairing on LH side	No start & no display	Replace
Turn signal flasher relay	Under front fairing on LH side	Turn signals no flash	Replace
Fan Relay	Under seat	No fan	Replace
Headlight Relay2 3	Under front fairing on LH side	No headlight	Replace (check bulbs too)
Battery4	Behind RH lower fairing	Starting issues, ECU shutdown	Charge or Replace
Side stand Bypass Switch	On top of side stand pivot point	Erratic starting	Replace
Sparkplug5	At top of both cyls	Slow starting, Fouled and no start	Check, Clean, Replace
Fuel Filter	Inside Tank	Low power at higher rpm	Replace. (check for split fuel lines)

¹ Models older than 2003 had a connector that could come off. Remedy: wire tie it on. Yamaha relay a common replacement.

² Relays can be replaced with alternate units for reliability. Greenwich Electronics AR4-012-A21S; Design Tech Engineering LLC; PO Box 293; Beaver Dam WI 53916; www.dotnet.com/~pyrodan/relay.htm

³ Ducati Designs headlight kit make this a spare.

⁴ For good battery performance keep it attached to a Batterytender or equal when not riding.

⁵ The stock Champion plugs can be replaced with NGK DCPR8E for better starts, lower cost