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Trane / American Standard S9X1 / S9X2 / S9B1 Furnace Codes
Covers the single-stage S9X1 and S9B1 and the two-stage S9X2. American Standard sells matching models; check the label on the unit.
| Code | Meaning | What to check |
|---|---|---|
| E01 | Loss of IRQ or other internal failure (internal IFC error). | Replace the integrated furnace control. |
| E2.1 | Retries exceeded: flame never sensed. One-hour lockout after 3 tries. | Gas supply, igniter, gas valve, flame sensor. How to fix → |
| E2.2 | Recycles exceeded: flame sensed then lost. One-hour lockout after 10 times. | Flame sensor, ground, gas pressure, pressure switch dropping out. How to fix → |
| E2.3 | 1st-stage gas valve not energized when it should be, 10 times. | Gas valve wiring and the circuit through the limits and pressure switch. How to fix → |
| E3.1 | 1st-stage pressure switch closed when it should be open (shorted). | Stuck switch or wiring short. How to fix → |
| E3.2 | 1st-stage pressure switch open when it should be closed. | Vent or intake blockage, condensate, hoses, inducer. How to fix → |
| E3.3 | 2nd-stage pressure switch closed when it should be open (S9X2 only). | How to fix → |
| E3.4 | 2nd-stage pressure switch open when it should be closed (S9X2 only). | How to fix → |
| E04 | Open limit: main thermal limit, rollout switch or reverse airflow switch. | Airflow first; rollout needs a vent and heat exchanger check. How to fix → |
| E05 | Flame detected when it should not be present. | Gas valve leaking through or flame sense circuit short. How to fix → |
| E6.1 | Line voltage polarity reversed. | Swap hot and neutral at the furnace. How to fix → |
| E6.2 | Bad grounding: incoming or chassis ground not sensed. | Verify the ground to the furnace and control. How to fix → |
| E6.3 | Igniter relay fault or igniter open. | Igniter and its wiring; replace the control if the relay is stuck. How to fix → |
| E7.1 | 1st-stage gas valve energized when it should be off (24 V present when it shouldn't be). | Gas valve wiring; external 24 V fed into the valve circuit. |
| E08 | Flame current low but still strong enough to operate. | Below about 0.5 microamps DC: clean the flame sensor, check ground. How to fix → |
| E09 | Open inducer limit switch or condensate pressure switch. | Condensate not draining freely: trap, drain line, hoses. |
| E11 | Gas valve circuit fault: valve not energized when it should be, or internal gas valve relay failure. | Gas valve wiring; replace the control if the wiring is good. |
| E12 | Open fuse (onboard 5 A fuse open or missing). | Short in the 24 VAC wiring. How to fix → |
How to read the codes
- The active error shows on the IFC display. The control's menu also includes a fault history.
- Codes with a decimal (for example E2.1) are sub-codes of the same fault family: 2.x ignition, 3.x pressure switch, 6.x power and igniter.
- Pressure switch codes 3.3 and 3.4 apply only to the two-stage S9X2.
Codes point to a circuit, not a part. Test before replacing anything, and never jumper a limit, rollout or pressure switch to keep a furnace running. Gas and line-voltage work is for trained technicians.
Source: Trane S9X1/S9X2/S9B1 Installation, Operation and Maintenance, FNR-SVX002A-EN (02/2026), Table 43 Error Codes and troubleshooting. The "meaning" column follows the manufacturer's wording; "what to check" is our field summary. Always go by the label on the furnace you're working on.
Related
- How to read furnace LED flash codes
- Furnace pressure switch troubleshooting
- Flame sensor microamps and cleaning
Other brands
- Lennox Merit ML180UH (80% single-stage)
- Carrier 58CVA / 58CVX (80% variable-speed two-stage)
- Rheem / Ruud R96V / 96MDV (96% two-stage communicating)
- Goodman / Amana GR9S80 / GD9S80 (80% single-stage)
- Lennox SL280UHV (80% two-stage variable speed)
- Goodman / Amana / Daikin GM9S96 / GC9S96 / GM9S92 (96% and 92% condensing, single-stage)
- Carrier 59TP6C two-stage condensing with InteliSense (Performance series)
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