Safety First: Always ensure the ignition is OFF when testing for resistance. Never probe connectors with excessive force, as this can spread the terminals and cause poor connections in the future.
Safety First: Always ensure the ignition is OFF when testing for resistance. Never probe connectors with excessive force, as this can spread the terminals and cause poor connections in the future.
The pick up coil (also known as the crank position sensor) is critical for your bike's ignition timing. If it fails, your Yamaha YZF-R125 may experience "no spark" conditions or intermittent stalling. Use this guide to diagnose a faulty sensor using a digital multimeter.
Testing Procedure
To check the health of the coil, you need to measure its internal resistance. This can be done at two points:
At the Sensor Solder Joints:
If you have the stator cover removed, test directly between the White wire and the Pink wire at the solder connections on the coil itself.
At the Wiring Connector:
Locate the connector block leading from the stator to the main harness. Testing here is often easier and confirms that the wiring between the sensor and the plug is intact.
To check the health of the coil, you need to measure its internal resistance. This can be done at two points:
At the Sensor Solder Joints: If you have the stator cover removed, test directly between the White wire and the Pink wire at the solder connections on the coil itself.
At the Wiring Connector: Locate the connector block leading from the stator to the main harness. Testing here is often easier and confirms that the wiring between the sensor and the plug is intact.
What to Look For
Resistance Values: Set your multimeter to the Ohms (Ω) setting. A healthy coil should show a specific resistance range (typically 248–372 ohms for this model, but always verify with your workshop manual).
Open Circuit: If the meter reads "1" or "OL", the internal winding is broken, and the coil must be replaced.
Short to Ground: Check for continuity between either wire and the engine casing. There should be no continuity (infinite resistance).
Resistance Values: Set your multimeter to the Ohms (Ω) setting. A healthy coil should show a specific resistance range (typically 248–372 ohms for this model, but always verify with your workshop manual).
Open Circuit: If the meter reads "1" or "OL", the internal winding is broken, and the coil must be replaced.
Short to Ground: Check for continuity between either wire and the engine casing. There should be no continuity (infinite resistance).
Symptoms of Failure
Engine cranks but will not start (no spark).
Intermittent cutting out once the engine gets hot.
Erratic RPM readings or backfiring.
If your resistance readings are out of spec, the pick up coil is likely faulty. Since these are often sold as part of the stator assembly, you may need to replace the entire unit or source a high-quality aftermarket sensor.
Engine cranks but will not start (no spark).
Intermittent cutting out once the engine gets hot.
Erratic RPM readings or backfiring.
If your resistance readings are out of spec, the pick up coil is likely faulty. Since these are often sold as part of the stator assembly, you may need to replace the entire unit or source a high-quality aftermarket sensor.
test between the white wire and the pink at the solder connections of pick up coil this will test coil
ill then do the same test but at the wiring connector block results should be the same or very similar and will let you know wiring is correct to connector .
Another video on this here
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