Yamaha Error Code 42: Speed Sensor: No Normal Signal

The ECU is not receiving a normal signal from the vehicle speed sensor, so the speedometer often stops working and the engine warning light (check engine light) comes on.

Medium risk

The engine usually keeps running, but the speedometer may read zero. Get it fixed soon and keep a close eye on your speed in the meantime.

What causes Yamaha error code 42

  • CommonBroken or rusted speedometer drive (gear or cable) at the wheel
  • CommonDamaged speed sensor
  • PossibleMissing or damaged sensor rotor (the part the sensor reads)
  • PossibleDamaged wiring or loose connector to the speed sensor
  • RareFaulty neutral, gear or clutch switch on models that use them in this check

How to check and fix it

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

  1. Broken or rusted speedometer drive (gear or cable) at the wheel. Find which wheel your model reads speed from (scooters often use the front wheel, many motorcycles use the rear wheel or the transmission). Lift that wheel and turn it by hand. If the speedometer does not move, check any speedometer gear for rust or broken teeth and any drive cable for a break.
  2. Damaged speed sensor. Inspect the sensor body and its tip for cracks or impact damage. Replace it if it is broken or if a test with a known good sensor clears the code.
  3. Missing or damaged sensor rotor (the part the sensor reads). Look at the magnetic ring or toothed rotor that the sensor reads (on the wheel, brake disc or sprocket side, depending on the model) and make sure it is present, clean and not cracked. It can be left out or damaged when the wheel or brake disc is serviced.
  4. Damaged wiring or loose connector to the speed sensor. Follow the sensor wire from the sensor to its connector and look for cuts or pinching, especially where it moves with the fork, swingarm or steering. Clean the connector pins and check each wire for continuity.
  5. Faulty neutral, gear or clutch switch on models that use them in this check. On some models this code also covers the neutral or gear position switch. If the speed sensor checks out, test those switches and their wiring.

Parts & tools you may need

  • Speedometer cable
  • Molybdenum grease
  • Digital multimeter

FAQ

My bike has a digital speedometer. Can a cable still be the problem?

Yes. Some scooters show speed on a digital display but still get it from a mechanical drive at the wheel. Check how your model is built before replacing electrical parts.

How do I read code 42 from a flashing check engine light?

Many Yamaha models that flash their codes show tens as long (slow) flashes and ones as short (fast) flashes, which would make this code four long flashes followed by two short (fast) flashes. Patterns can differ between models, so check the information for your bike.

Sources

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