Trane Furnace Code E3.4
Soft lockout
The second-stage pressure switch will not close, so the furnace cannot go to high fire.
Manual wording: “Open Pressure Switch, 2nd Stage”
Documented for: Two-stage S8V2, S9V2 and S9V2-VS furnaces
Likely causes, most common first
- Open pressure switch, 2nd stage
- Restricted or blocked venting
- Draft inducer not reaching high-stage speed
- Pressure switch tubing problem
What you can safely check yourself
- Check the outdoor intake and exhaust terminations for blockage
- Check the condensate drain and trap for a clog (condensing models)
When to call a technician
If the venting is clear, the second-stage pressure switch or inducer needs a technician.
A Trane furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.
Sources
- Installer's Guide - Upflow/Horizontal and Downflow Gas-Fired, Direct/Non-Direct Vent, 2-Stage Condensing Variable Speed Furnaces (18-CE01D1-1E-EN) (Trane, S9V2B040U3PSAA through S9V2D120D5PSAA two-stage condensing variable-speed furnaces) · checked 2026-08-25
- Installation, Operation, and Maintenance - Gas-Fired 2-Stage Condensing Variable Speed Furnaces with Variable Speed Draft Inducer (FNR-SVX001B-EN) (Trane, S9V2B040U3VSBB through S9V2D120D5VSBB (S9V2-VS) two-stage condensing variable-speed furnaces) · checked 2026-08-25
- Installation, Operation, and Maintenance - Link Communicating or 24 Volt Gas-Fired 2 Stage Induced Draft Furnaces with Variable Speed Motor (FNR-SVX003A-EN) (Trane, S8V2A040M3PCB through S8V2D120M5PCB two-stage 80% induced draft furnaces (communicating or 24V)) · checked 2026-08-25