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:

    Assembling the front wheel
    1. Install: Wheel bearings Oil seal a. Install the new wheel bearings and oil seal in the reverse order of disassembly. CAUTION:Do not contact the wheel bearing inner race "1" or balls "2". Contact should be made only with the outer race "3". NOTE: Use a socket " ...

    Removing the front brake caliper
    NOTE: Before disassembling the brake caliper, drain the brake fluid from the entire brake system. 1. Remove: Brake hose union bolt "1" Copper washers "2" Brake hose "3" NOTE: Put the end of the brake hose into a container and pump out the brake fluid carefully. ...

    Engine break-in
    There is never a more important period in the life of your engine than the period between 0 and 1000 km (600 mi). For this reason, you should read the following material carefully. Since the engine is brand new, do not put an excessive load on it for the first 1000 km (600 mi). The vari ...

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