Yamaha PW error 79: DC/DC converter abnormal current detected
The controller has detected abnormal DC current flowing through the internal DC/DC converter that supplies the display and auxiliary circuits. Motor assist is cut, walk assist is disabled, and the bike will not operate normally until the fault clears. Speed and torque readings drop out as long as the code is active.
| Drive system | Yamaha PW series (PW-X3, PW-S2, PW-ST, PWseries CE - also Giant SyncDrive) |
| Severity | Dealer needed |
| Keep riding? | Do not keep riding |
| Typical cost | Expect a dealer diagnostic around €40-80, a replacement DC/DC harness connector at roughly €20-60, and a full controller assembly at €250-450 including fitting. |
Likely causes
- Corroded or wet external DC/DC connector at the controller or display harness
- Damaged wiring between the controller and display (chafed insulation, pinched loom at the head tube)
- Failed display drawing abnormal load on the 5V/12V rail
- Internal controller DC/DC converter fault (regulator IC failure)
- Water ingress into the controller housing or connector block
- Short circuit in a connected accessory such as a light cable or USB port
How to fix Yamaha PW error 79
- Stop riding and power off the system; remove the battery before inspecting any connector.
- Unplug and inspect the external DC/DC connector between the display and controller for moisture, green corrosion, or bent pins, then reconnect it firmly.
- Trace the display harness along the frame and check for chafing, pinch points, or damaged insulation, especially at the head tube and under the down tube cover.
- Refit the battery, switch the display on, and ride briefly to see if code 79 returns.
- If 79 reappears, leave the system off and book the bike in at an authorised Yamaha or Giant SyncDrive service dealer.
- The dealer will test the DC/DC converter output on a diagnostic and replace either the external DC/DC connector or the full controller assembly.
Warranty: A genuine DC/DC converter or controller fault inside the two-year warranty period is normally covered, but water ingress, crash damage, and connectors corroded through poor maintenance are treated as owner fault.
Typical cost: Expect a dealer diagnostic around €40-80, a replacement DC/DC harness connector at roughly €20-60, and a full controller assembly at €250-450 including fitting.
Frequently asked
Can I reset yamaha error 79?
Yes. Switch the display off, wait five seconds, then power the system back on. If the controller no longer detects abnormal DC current at start-up, the code clears and assist returns. If it comes back straight away, the fault is still present and a dealer must trace it.
Is it safe to keep riding with this code active?
No. Motor assist is cut and the system can shut down again mid-ride, leaving you without power on a hill or at a junction. The fault points to an electrical problem in the converter circuit, and continuing to ride risks further damage to the controller.
How much will the repair cost and is it covered by warranty?
A dealer diagnostic runs €40-80, a new DC/DC connector €20-60, and a controller assembly €250-450 fitted. Inside the two-year warranty a genuine component fault is covered; water damage or crash damage is not.
Related Yamaha PW codes
Manuals and video
Official source: cdn2.yamaha-motor.eu
Not an official Yamaha PW document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.