Hi, Scott it should be noted that the reasons your EFI light stays on constantly or flashes and your bike will or will not start and may turn over or not, these conditions will vary from bike to bike depending on the year, make, and model and you should always refer to your owners/service manual for proper diagnostic procedures. It should also be noted that any type of prior work done to the bike or an abnormal event occurrence IE: adding accessories, electrical curiosity/adventures, laying bike down/crashes, rainstorms/bike washings just before EFI light issues started can be significant hints/aids into tracking down the gremlin, also carry the appropriate jumper wire to access fault codes to reduce the risk of being stranded or towed, that being said the usual suspects are:
1. Faulty Fuel Pump, fuse or system relay switch.
2. Battery starting to fail due to old age/damage, perform a load test.
3. Discharged battery, check battery terminals for damage or corrosion, check the battery cables at "BOTH" ends for loose, corroded, or broken connectors, "INSIDE" and outside the cable harness, perform connector wiggle test and check cables with an ohmmeter if necessary.
4. Faulty switches/sensors: run/off, ignition, clutch lever, neutral, side stand, tip over, fuel, and or their connections.
5. Broken wire or worn insulation exposing wire to a ground situation especially inside wire harness at tight bends around fairing brackets, under dash panels, under fuel tanks over cylinder heads etc. Many harnesses are open on the ends that will allow water to enter and accumulate at v-bends.
Dielectric grease and contact cleaner are your best friends for wire/cable/harness connectors, look for corroded, broken, or loose pins/sockets.
For more information about your question and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
FI CODE FLASHING
Yamaha Fault Codes
Yamaha XC125 Service Manual
OEM parts for Yamaha
YAMAHA VITY XC125E Owner Manual
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