Yamaha YZF-R125 Service Manual: Checking the speed sensor

1. Check:

Speed sensor output voltage Out of specification → Replace.


a. Connect the pocket tester (DC 20 V) to the speed sensor coupler (wire harness end) as shown.


  • Positive tester probe gray "1"
  • Negative tester probe gray/black "2"

Checking the speed sensor


b. Set the main switch to "ON".

c. Elevate the front wheel and slowly rotate it.

d. Measure the voltage of gray and gray/black.

With each full rotation of the front wheel, the voltage reading should cycle from 0 V to 5.0 V to 0 V to 5.0 V.

    Checking the fuel sender
    1. Drain the fuel from the fuel tank. 2. Check: Fuel sender resistance Out of specification → Replace the fuel sender. a. Connect the pocket tester ( × 10) to the fuel sender c ...

    Checking the radiator fan motor
    1. Check: Radiator fan motor Faulty/rough movement → Replace. a. Disconnect the radiator fan motor coupler from the wire harness. b. Connect the battery (DC 12 V) as shown. Posi ...

    Other materials:

    Circuit diagram
    4. Main fuse 5. Main switch 9. Battery 14.Neutral switch 25.ECU (engine control unit) 31.Fuel sender 34.Rear brake light switch 35.Front brake light switch 37.Tail/brake light 38.Rear right turn signal light 39.Rear left turn signal light 40.Front right turn signal light 41.Front lef ...

    Installing the drive chain
    1. Lubricate: Drive chain Master link 2. Install: Drive sprocket Drive sprocket retainer bolts 3. Install: Master link O-rings Master link plate Master link clip "1" CAUTION: The closed end of the master link clip must face in the direction of drive ch ...

    Indicator and warning lights
    Indicator and warning lights Neutral indicator light"" Turn signal indicator light"" High beam indicator light"" Engine trouble warning light"" Coolant temperature warning light"" Turn signal indicator light"" This indicator light flashes when the turn signal switch is pushed t ...

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