Yamaha PW error E8: Battery voltage abnormal

Yamaha PW series (PW-X3, PW-X2, PW-X, PW-ST, PW-TE, PW-SE, PW-CE) and Giant/Liv SyncDriveDealer neededRide with caution

E8 is shown when the battery voltage is outside the range the drive unit expects, either too low after deep discharge or inconsistent during load. Assist stops. A deeply discharged pack sometimes recovers with a full charge; a pack with a bad cell group does not. Also shown on Giant/Liv (SyncDrive) bikes, sometimes with a leading zero (E01) or as 'Er' followed by the number on older Yamaha displays.

Likely causes

Battery stored flat for a long time
Ageing pack with high internal resistance
Poor contact causing voltage drop under load
BMS fault

How to fix Yamaha PW error E8

Charge the battery fully with the original charger and watch that the charger finishes normally
Clean and reseat the battery
Power-cycle and test under load on a short ride
If E8 returns under load, dealer battery test

Go to a dealer if: Dealer with the Yamaha/Giant diagnostic tool (Yamaha PW diagnostic or Giant's RideControl/e-bike diagnostic software) is needed to read the fault log and test the component when the home checks do not clear the code.
Warranty: Component faults inside the drive unit, battery or display are covered by the bike brand's warranty via the dealer; damage from crashes, water ingress or tuning devices is not.
Typical cost: A full charge is free; a replacement battery is expensive.

Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.

Frequently asked

Can I reset E8 myself?

Sometimes, by fully charging the battery; if it returns it is a pack fault.

Can I keep riding with E8?

Pedal home unassisted; do not keep riding a pack that sags under load.

Is E8 covered by warranty?

Yes within the battery's warranty period for a genuine fault.

Related Yamaha PW codes

E6 · Battery communication error E7 · Battery abnormality

Not an official Yamaha PW document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.