Yamaha Error Code 12: Crankshaft Position Sensor: No Normal Signal

The ECU is not getting a usable signal from the crankshaft position sensor, so it cannot time the spark and fuel and the engine will usually not start or will cut out.

High risk

The engine can stop without warning, including while riding. Do not ride the bike until the cause is found.

What causes Yamaha error code 12

  • CommonLoose, dirty or corroded crankshaft position sensor connector
  • CommonWeak battery or a failing starter relay making cranking too slow
  • PossibleDamaged wiring between the sensor and the ECU
  • PossibleFailed crankshaft position sensor
  • RareSensor face damaged or the pickup rotor loose or out of position

How to check and fix it

Start at the top: the most likely and usually cheapest checks come first.

  1. Loose, dirty or corroded crankshaft position sensor connector. Find the sensor connector (follow the wire from the sensor on the engine to its plug in the harness), unplug it, look for green corrosion or pushed-back pins, then plug it back in firmly and see if the code returns.
  2. Weak battery or a failing starter relay making cranking too slow. Charge the battery fully and test it under load. If the engine cranks slowly, check the starter relay and battery terminals before replacing any sensor.
  3. Damaged wiring between the sensor and the ECU. Follow the sensor wires along the harness and look for chafing, melted insulation or pinched sections near the engine and frame. Check each wire for continuity end to end with a multimeter.
  4. Failed crankshaft position sensor. Measure the sensor's resistance at its connector and compare it with the value in the service information for your model. Replace the sensor only if it is out of range or physically damaged.
  5. Sensor face damaged or the pickup rotor loose or out of position. With the cover removed, look at the tip of the sensor for scoring and make sure the rotor it reads from is tight. A worn cam chain tensioner or loose parts inside the cover can grind the sensor.

Parts & tools you may need

  • Digital multimeter
  • Motorcycle battery charger
  • Electrical contact cleaner

FAQ

Will code 12 clear by itself?

On some models the warning may go out once the ECU sees a good signal again, but the fault can stay stored in the ECU's history and the cause is still there. If it does not go out, or keeps coming back, follow the checks above and have the bike checked by a dealer.

Can a bad battery really cause code 12?

Yes. If the engine turns over too slowly, the ECU may not see a clean signal from the sensor. Owners have cleared repeated code 12s by fixing the battery or starter relay.

Sources

Last updated: