Generac Code 1902: Undervoltage and How to Clear It
1902 is an undervoltage alarm. You'll see it called "under speed" on forums and third-party code lists — that is wrong, and Generac's own code list settles it: 1900–1916 are Undervoltage, 1600–1603 are Underspeed, and the panel itself reads UNDERVOLTAGE. What Generac publishes for the number is what it publishes for the whole range: "The generator is not producing proper voltage. This could result from prolonged under voltage or sudden voltage loss." The owner-level checks are fuel selection, fuel jet position, propane above 30 % and a clear, dry air intake. If those are right, what follows is a voltage measurement on a running machine — a dealer's job, not yours.
| Code | 1902 (UNDERVOLTAGE) |
|---|---|
| Applies to | Guardian 10–26 kW and Next Generation 10–28 kW air-cooled (2017 and newer), Evolution / Evolution 2.0 controllers; Generac publishes 1900–1906 as one condition |
| Severity | Unit will not run |
| DIY | Check, then call — owner-level checks first, then a dealer |
| Last checked |
What code 1902 means
Generac does not publish a separate definition for 1902. Its support article for the 1900-series covers the numbers together — "The generator is not producing proper voltage. This could result from prolonged under voltage or sudden voltage loss" — and applies to Guardian 10–26 kW and Next Generation 10–28 kW units built from 2017 on. The sub-code exists to tell a technician which way the voltage went; it does not change anything an owner does.
So the practical content of a 1902 is this: the engine ran, and the controller did not see usable output. Generac's undervoltage article puts the causes in two groups: fuel supply or selection — a wrong fuel setting, a low tank, storm-time gas supply — and the electrical side, "circuitry, firmware, or voltage production." Its owner checks cover the first group. The second, it says, "typically requires advanced diagnosis by a Generac Independent Authorized Service Dealer."
This page exists for one reason beyond those checks: the number is routinely published elsewhere as an underspeed code, and acting on that sends you after the engine when the panel is reporting voltage. For the full family — what the range covers, where Generac's own pages disagree about it, and the complete owner procedure — see code 1900.
| Code | Display | Meaning (Generac wording) | Severity | DIY? |
|---|---|---|---|---|
| 1900–1906 | UNDERVOLTAGE | "The generator is not producing proper voltage. This could result from prolonged under voltage or sudden voltage loss." No separate definition is published for 1901, 1902 or 1906 | Unit will not run | Check, then call |
| 1600–1603 | UNDERSPEED | "Engine speed (RPM) is too slow" — a different family, a different article, a different first check | Unit will not run | Check, then call |
Older Nexus controllers (pre-2013) don't use numeric codes at all; they show UNDERVOLTAGE as a text alarm, and the checks on this page still apply.
How to clear Generac code 1902
1902 can be cleared once, after the fuel and air checks, with a MANUAL start and nothing connected. The owner's manual's whole entry for UNDERVOLTAGE is "Contact an IASD," and Generac's undervoltage article strongly recommends a dealer if it persists. Clear it a single time, and if 1902 comes back, stop. Each controller's key presses are on Generac lights and alarms.
Generac's undervoltage article covers 1902 inside the 1900 range and allows the owner one attempt: "You can attempt to clear the alarm and manually restart the unit," adding "Sometimes, clearing the alarm and attempting to restart the unit is all that is needed, as the alarm may be a one-time occurrence that does not indicate a persistent issue." Its warning for the restart: "Never start a generator while under load." The Quick Reference Guides are shorter still: UNDERVOLTAGE, "Contact an IASD." (Guardian A0001846499 Rev. C, p. 34; Next Generation A0004332577 Rev. C, p. 38).
Why code 1902 can appear during a storm
Generac names one cause for 1902 by number, and it is outside the generator: fuel supply during a big outage. When demand on the gas grid rises, or the grid is damaged, during a big outage, the unit can get less fuel than it needs. The article's advice is to call the gas company, not to clear the alarm repeatedly. On propane, the equivalent check is the tank level.
The undervoltage article's note, verbatim: "In extreme weather event circumstances, heavy load on the fuel supply grid may result in a decrease in available fuel to the unit, which may result in an error 1902." For an outage on natural gas it says: "During widespread outages and when operating on natural gas, contact your gas company to check on the stability of the natural gas grid," because "Increased demand or damage to the grid during significant outage events can impact grid supply." On propane it asks you to "verify fuel levels are above 30%."
Checks before calling about a 1902
- What else is in the alarm log? From MAIN MENU go to HISTORY → ALARM LOG, and write down every code with its time before you clear anything; the dealer will want the sequence.
- If the log shows 1100 first → work through the 1100 checks before anything below.
- Fuel selection and supply. The support article asks you to verify the fuel source selection (natural gas vs. propane) matches the installation, that the fuel jet is in the correct position, and that a propane tank is above 30 %.
- If propane is low → fill it and retest.
- If you suspect the selection or jet is wrong → dealer. Don't move the jet yourself.
- Air intake. Clear snow, leaves, and moisture from the intake and check the air filter (0J8478S for 14–26 kW, 0E9371AS for 10 kW). The support article's cold-weather note: "moisture can freeze in the air filter, preventing adequate airflow to the engine."
- Natural gas during a storm? Call the gas company about supply, per the section above.
- Clear and test. Clear the alarm once and run in MANUAL with no load.
- Still 1902? Stop. Generac: "If issues persist after performing the checks and attempting to restart, contacting a Generac IASD for diagnosis is strongly recommended."
Air filter numbers for a 1902 check
There's no owner-replaceable part for a genuine 1902; the electrical side is the dealer's. The air filter below is the one item Generac's owner checks touch, in its cold-weather note that moisture can freeze in the filter and starve the engine of air. The numbers are from the 10–26 kW owner's manual.
| Part | Part number | Fits | Where verified |
|---|---|---|---|
| Air filter | 0J8478S | 14–26 kW air-cooled | Owner's manual A0001846499 |
| Air filter | 0E9371AS | 10 kW air-cooled | Owner's manual A0001846499 |
When a 1902 needs a dealer
- 1902 returns after one clean reset with fuel and air confirmed.
- The generator runs but the house has no power, or the lights flicker and dim when it's running — that's the same undervoltage seen from inside.
- You see burn marks, a hot smell, or a tripped main breaker on the generator.
- The alarm log shows 1902 with any 2100-series (overload) or 1600-series (underspeed) codes.
- Generac support: 1-888-436-3722. Warranty repairs go through an Independent Authorized Service Dealer.
Undervoltage, underspeed and the 1900 range
1902 sits inside the 1900–1906 range, and its fuller procedure is on the 1900 page. 1600 Underspeed is a different alarm — Generac's list keeps 1600–1603 separate — though it shares fuel supply among its causes ("The unit is overloaded or has fuel supply issues"). A generator that runs but delivers no power to the house without any alarm is a transfer-switch question: runs but no power. How the red alarm light differs from the yellow warning light is covered on the lights and alarms page.
Not sure the generator can carry the load?Generator Wattage Calculator Running watts, the largest starting surge, and a generator class from manufacturer charts.Frequently asked questions
Is Generac 1902 "under speed"?
No. Generac's official code list assigns 1900–1916 to Undervoltage and 1600–1603 to Underspeed. The confusion comes from third-party code lists that mislabel it. The display on the unit says UNDERVOLTAGE.
Can a weak battery cause code 1902?
Generac does not list the battery among the causes for this family, and a battery weak enough to matter usually announces itself with its own codes — 2750, 2770 or an overcrank. Reading the BATTERY menu costs nothing while you are at the panel, and it is worth telling the dealer what it said, but do not expect a new battery to clear an undervoltage.
My generator threw 1902 during a storm and now starts fine. Do I still need service?
Generac allows that it may not: its article says an alarm "may be a one-time occurrence that does not indicate a persistent issue," and it names storm-time fuel supply as a cause of 1902 specifically. If it returns, or happens with fuel and air confirmed, Generac's advice is a dealer.
Why do other sites say 1902 is an underspeed code?
Because third-party code lists copy each other. Generac's own list assigns 1900–1916 to Undervoltage and 1600–1603 to Underspeed, and the display on the unit says UNDERVOLTAGE. If a page tells you to start with engine speed on a 1902, it is working from the wrong family.
Does Mobile Link report 1902?
Yes. The listed message for the whole 1900–1916 family is "The generator has experienced an undervoltage alarm. Please contact a dealer," and the status history shows the number if the unit is enrolled.