Yamaha Error Code 34: Ignition Coil (Cylinder #2): Primary Circuit Fault

The ECU reports a primary-circuit fault on the ignition coil it calls #2. On bikes where one coil fires two cylinders, such as the FZ6, that is the coil shared by cylinders #2 and #3, so two cylinders can drop out at once.

Medium risk

With one coil out, an inline-four may carry on with only two cylinders firing — noticeably down on power and vibrating. You can usually get home slowly, but do not plan a long ride until it is fixed.

What causes Yamaha error code 34

  • CommonSpade terminal inside the coil boot not pushed into its socket
  • CommonCoil #2 failing, often only once it is hot
  • PossibleHarness damage on the #2 coil feed
  • RareFailed ignition driver inside the ECU

How to check and fix it

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

  1. Spade terminal inside the coil boot not pushed into its socket. Peel back the rubber boot on coil #2's low-voltage lead. A terminal can sit inside the boot and look connected while never touching the coil's pin, which makes cylinders cut in and out as the bike vibrates. Push it fully home and confirm it grips.
  2. Coil #2 failing, often only once it is hot. Swap coil #2 with the coil for another cylinder pair. If the code changes to the other coil's number, the coil is at fault; if it stays at 34, look at the wiring and ECU instead. Resistance checks can miss a coil that only breaks down when warm.
  3. Harness damage on the #2 coil feed. Follow the coil #2 wires to the main harness and check each for continuity while flexing the harness, since a break may only open up with movement or heat.
  4. Failed ignition driver inside the ECU. If the coil swap and wiring checks all pass and 34 keeps coming back, the ECU's output for that coil may be damaged. One FZ6 owner found a burned part inside the ECU; this is the last thing to suspect, not the first.

Parts & tools you may need

  • Digital multimeter
  • Replacement ignition coil (check the part number matches your model and year)

FAQ

My FZ6 suddenly runs on two cylinders. Is that code 34?

It fits. On the FZ6 each coil fires a pair of cylinders, so losing the #2 coil takes out cylinders #2 and #3 together. Code 33 is the matching code for the #1 and #4 pair.

Could a shop have misdiagnosed code 34 as a bad coil?

It happens. One owner was quoted for new coils and then found the real problem was a coil terminal that had never been seated. Check the connection before paying for parts.

Sources

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