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:

    Checking the brake fluid level
    Front brake Front brake Minimum level mark Rear brake Rear brake Minimum level mark Insufficient brake fluid may allow air to enter the brake system, possibly causing it to become ineffective. Before riding, check that the brake fluid is above the minimum level mark an ...

    Air induction system
    1. Air induction system hose (air filter case to reed valve assembly) 2. Air induction system reed valve assembly 3. Air induction system hose (reed valve assembly to exhaust pipe) Checking the air induction system Air injection The air induction system burns unburned exhaust gases b ...

    Replacing the rear brake pads
    NOTE: When replacing the brake pads, it is not necessary to disconnect the brake hose or disassemble the brake caliper. 1. Remove: Brake pads Brake pad spring NOTE: To remove the inner brake pad "1", push down on the brake caliper bracket so that there is space to remove the brake pa ...

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