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:

    Front wheel
    To remove the front wheel WARNING To avoid injury, securely support the vehicle so there is no danger of it falling over. Loosen the front wheel axle pinch bolt, then the wheel axle and the brake caliper bolts. Front wheel axle pinch bolt Lift the front wheel of ...

    Faulty front fork legs
    Leaking oil - Bent, damaged or rusty inner tube - Cracked or damaged outer tube - Improperly installed oil seal - Damaged oil seal lip - Incorrect oil level (high) - Loose damper rod assembly bolt - Damaged damper rod assembly bolt copper washer - Cracked or damaged front fork cap O-ring M ...

    Assembling the main axle and drive axle
    1. Install: Toothed washer "1" Circlip "2" NOTE: Be sure to install the circlip so that its sharp edge "a" is facing away from the toothed washer and gear. Be sure the circlip ends "b" are positioned at the axle spline groove "c". 2. Install: 2nd pinion gear "1" NO ...

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