1906 — Undervoltage Fault

Code 1906 falls in Generac's 1900-1916 fault range and represents an UNDERVOLTAGE fault: the generator is not producing proper output voltage. This can appear as a prolonged undervoltage condition or a sudden voltage loss while the unit is running. Generac attributes this range to fuel supply/selection, excitation circuitry, firmware, or voltage-production issues, and notes that advanced diagnosis by an authorized dealer is usually required.

Fuel supply or fuel selection issue: On dual-fuel units, an incorrect fuel selector setting or inadequate fuel supply/pressure can prevent the engine from running at the speed needed for proper voltage. Excitation circuit fault: A problem in the exciter/AVR circuitry that builds alternator output. Controller firmware issue: Generac lists firmware as one of the documented causes for this fault range.

Limited use only. This is rated a serious-severity fault.

If this is a dual-fuel unit, confirm the fuel selector is set to the fuel you're actually running and that supply/pressure is adequate — this is the one owner-checkable item in Generac's documented cause list. Clear the fault from the controller and run the unit through a manual exercise cycle to see if 1906 returns. If it returns, this points to excitation circuitry, firmware, or the alternator's voltage-production path — Generac states advanced diagnosis by an authorized dealer is usually required. Do not attempt exciter, AVR, or stator-level repair yourself; these are high-voltage components.