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Fujitsu code 51: indoor unit fan motor error

By How House Works EditorialBased on Fujitsu manualsChecked against sources Updated

Fujitsu display

51

“Indoor unit fan motor error (Indoor unit)”

KPAS, KPBS, KNAS, KMAS, KZAS, KTAS, ASLH, LZBS, LZAS, LMAS, LPAS · KPAS/KPBS service p. 03-2; KNAS service p. 03-2; KMAS service p. 03-2; KZAS service p. 03-2; KTAS service p. 03-2; ASLH service p. 03-2; LZBS service p. 03-2; LZAS service p. 03-2; LMAS service p. 03-2; LPAS service p. 03-2
Technician

OPERATION 5 / TIMER 1. Set when the indoor fan runs below 1/3 of its target speed for more than 56 seconds (KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-43). KNAS prints it without “(Indoor unit)”. KPAS installation manual: “Indoor unit fan motor error” (KPAS Installation Manual, p. En-16).

What it means

Code 51 is an indoor unit fan motor error. In the installation manuals’ lamp tables it is five OPERATION blinks and one TIMER blink, repeated, while ECONOMY blinks fast KPAS Installation Manual, p. En-16; LZBS Installation Manual, p. En-11; RLS3 Installation Manual, p. En-11.

The indoor unit’s main PCB sets it when the fan’s actual speed stays below 1/3 of the target speed for more than 56 seconds. The causes listed are a fan rotation failure, an open fan motor winding, motor protection after the temperature around the motor rises, a failed main PCB and a failed fan motor KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-43. The RLS3 Service Instructions print the same 1/3 and 56-second rule p. 02-10.

On KPAS and KPBS units the mobile app table splits it into 51.1, “Indoor unit fan motor 1 lock error”, and 51.2, “Indoor unit fan motor 1 rotation speed error” KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-8.

Check these first

Fujitsu’s owner’s manuals give no owner fix for this code. The steps are the same as for any code; the manuals’ wording is on the code 11 page.

  1. Check that it is an error code: OPERATION and TIMER blink while ECONOMY blinks fast KPAS Operation Manual, p. En-13.
  2. Read the code with Service check if your remote has it KPAS Operation Manual, pp. En-13–En-14.
  3. Stop the unit, turn off its breaker and consult authorized service personnel, as the manuals require for this lamp pattern RLS3 Operation Manual, p. En-10; KPAS Operation Manual, p. En-12. This is separate from their rule against using the breaker for everyday on and off KPAS Operation Manual, p. En-2.
  4. Give them the code KPAS Operation Manual, p. En-14.

The owner’s manuals do not ask you to turn the indoor fan by hand; that check is in the service manual KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-43.

When to call a licensed technician

The KPAS/KPBS service manual’s checks for 51, in order KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-43:

  • With operation off, turn the fan by hand to see whether it is caught, has come off or the motor is locked. Replace the fan or bearing if it is abnormal.
  • Check for excessive heat around the motor from nearby equipment. Restart once the temperature has come down.
  • Check the indoor fan motor and replace it if it is abnormal.
  • If none of these improves the symptom, replace the main PCB.

Fujitsu warns of electric shock and sets a waiting time after power-off before electrical components are touched: 5 minutes in the service manual, 10 minutes in the KPAS installation manual KPAS/KPBS Service Manual SR_AS142ES_09, p. 02-1; KPAS Installation Manual, p. En-2.

Notes for different models

  • The other K-series service manuals have their own sections for 51 KNAS Service Manual SR_AS159ES_02, pp. 03-41–03-42; KMAS Service Manual SR_AS134ES_03, p. 03-39; KZAS Service Manual SR_AS137ES_03, p. 03-40; KTAS Service Manual SR_AS147ES_04, p. 03-41; ASLH Service Manual SR_AS143ES_03, p. 03-33, and so do the L-series ones LZBS Service Manual SR_AS048EF_02, p. 03-20; LZAS Service Manual SR_AS024EF_09, p. 03-20; LMAS Service Manual SR_AS058EF_04, p. 03-13; LPAS Service Manual SR_AS050EF_03, p. 03-13.
  • RLS3-era tables call it “Indoor unit fan motor error” RLS3 Service Manual, p. 7, and their service instructions have a section for it RLS3Y Service Instruction, p. 02-14; RLB Service Instructions, p. 02-10; RLS2 Service Instructions, p. 02-10; RLFW1 Service Instruction, p. 02-10.
  • Two other K-series codes name the indoor unit’s motor: 33, “Indoor unit motor electricity consumption detection error”, and 39, “Indoor unit power supply error for fan motor” KPAS/KPBS Service Manual SR_AS142ES_09, p. 03-2. Installation manual lists add 59 and 5A for a second and third indoor fan motor, which no service manual table used here includes KPAS Installation Manual, p. En-16.

Related Fujitsu codes

  • 33 “Indoor unit motor electricity consumption detection error (Indoor unit)”
  • 39 “Indoor unit power supply error for fan motor (Indoor unit)”

See also

Other ductless mini-splits: Daikin, Mitsubishi Electric, MrCool

All Fujitsu codes

Fujitsu is a trademark of its owner. How House Works is not affiliated with or endorsed by Fujitsu.

Sources

  1. GENERAL Inc.. KPAS/KPBS Service Manual SR_AS142ES_09. Document code SR_AS142ES_09, page stamp 2026.06.18; covers ASUH09–36KPAS/KPBS and AOUH09–36KPAS1. The 2026 revision. It adds code 45, which the earlier revision SR_AS142ES_04 does not list.. Accessed Oct 12, 2026.
  2. Fujitsu General America / GENERAL HVAC Solutions America (document portal). KPAS Installation Manual. PART No. 9387603408-01; KP series; no publication date printed. Accessed Oct 12, 2026.
  3. Fujitsu General America / GENERAL HVAC Solutions America (document portal). KPAS Operation Manual. PART No. 9387602548-01; KP series; no publication date printed. Accessed Oct 12, 2026.
  4. Fujitsu General Limited. KNAS Service Manual SR_AS159ES_02. Document code SR_AS159ES_02, page stamp 2025.10.08; covers ASUH09–24KNAS and AOUH09–24KNAS1. Accessed Oct 12, 2026.
  5. Fujitsu General Limited. KMAS Service Manual SR_AS134ES_03. Document code SR_AS134ES_03, page stamp 2024.11.11; covers ASUH09/12KMAS and AOUH09/12KMAS1. Accessed Oct 12, 2026.
  6. Fujitsu General Limited. KZAS Service Manual SR_AS137ES_03. Document code SR_AS137ES_03, page stamp 2025.01.09; covers ASUH09–24KZAS and AOUH09–24KZAH1. Accessed Oct 12, 2026.
  7. Fujitsu General Limited. KTAS Service Manual SR_AS147ES_04. Document code SR_AS147ES_04, page stamp 2025.07.30; titled Service Manual for Cold Climate Region; covers ASUH09/12/15KTAS and KTAB with AOUH09/12/15KTAP1. Accessed Oct 12, 2026.
  8. Fujitsu General Limited. ASLH Service Manual SR_AS143ES_03. Document code SR_AS143ES_03, page stamp 2024.11.11; covers ASLH09/12KNAS and AOLH09/12KNAS1, 115 V. Its code table prints blink counts only, with no wired remote controller code column.. Accessed Oct 12, 2026.
  9. Fujitsu General Limited. LZBS Service Manual SR_AS048EF_02. Document code SR_AS048EF_02, page stamp 2022.10.14; covers ASUG09–15LZBS and AOUG09–15LZAS1. Accessed Oct 12, 2026.
  10. Fujitsu General America / GENERAL HVAC Solutions America (document portal). LZBS Installation Manual. PART No. 9387603187; no publication date printed. Accessed Oct 12, 2026.
  11. Fujitsu General Limited. LZAS Service Manual SR_AS024EF_09. Document code SR_AS024EF_09, page stamp 2022.10.12; covers ASUG09–15LZAS and AOUG09–15LZAS1. Accessed Oct 12, 2026.
  12. Fujitsu General Limited. LMAS Service Manual SR_AS058EF_04. Document code SR_AS058EF_04, page stamp 2022.10.05; covers ASUH09/12LMAS and AOUH09/12LMAS1. Accessed Oct 12, 2026.
  13. Fujitsu General Limited. LPAS Service Manual SR_AS050EF_03. Document code SR_AS050EF_03, page stamp 2022.10.18; covers ASUH09/12LPAS and AOUH09/12LPAS1. Accessed Oct 12, 2026.
  14. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS3 Service Manual. No document code printed; the error table page is stamped 2015.01.06; covers ASU9/12RLS3 and AOU9/12RLS3. Accessed Oct 12, 2026.
  15. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS3 Service Instructions. No document code or date printed; covers ASU9/12/15RLS3 and AOU9/12/15RLS3. Accessed Oct 12, 2026.
  16. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS3 Installation Manual. PART No. 9320456016; no publication date printed. Accessed Oct 12, 2026.
  17. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS3 Operation Manual. PART No. 9320455026; no publication date printed. Accessed Oct 12, 2026.
  18. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS3Y Service Instruction. No document code or date printed; covers ASU9/12/15RLS3Y and AOU9/12/15RLS3. The cover is stamped “TENTATIVE”.. Accessed Oct 12, 2026.
  19. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLB Service Instructions. No document code or date printed; covers ASU18/24RLB and AOU18/24RLB. Accessed Oct 12, 2026.
  20. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLS2 Service Instructions. No document code or date printed; covers ASU9/12/15RLS2 and AOU9/12/15RLS2. Accessed Oct 12, 2026.
  21. Fujitsu General America / GENERAL HVAC Solutions America (document portal). RLFW1 Service Instruction. No document code or date printed; covers ASU9/12RLF1 and AOU9/12RLFW1. Accessed Oct 12, 2026.