Trane furnace E3.3: Shorted pressure switch, second stage
E3.3 means the second stage pressure switch reads closed before the inducer starts. Like its first stage counterpart, it means the switch cannot prove draft and the furnace will not proceed.
Applies to: Trane and American Standard S9V2 two-stage condensing variable speed gas furnaces with a seven-segment integrated furnace control display, per Installer's Guide 18-CE01D1-1E-EN.
What it means
The second stage pressure switch exists to prove the higher draft that full firing rate requires, and the control checks it open at the same point in the sequence as the first stage switch. Finding it closed has the same meaning and the same consequence: an interlock that always reads closed is not an interlock. What differs from the open-circuit version of this fault is the symptom. An open second stage switch leaves a furnace that runs on low fire and never reaches full output — annoying but not dangerous. A shorted one stops the furnace at the pre-start check, so this presents as no heat rather than as poor heat.
Most common causes
- A failed second stage pressure switch with stuck or welded contacts.
- A short in the second stage switch wiring.
- A jumper left across the switch after earlier service.
- A switch of the wrong specification fitted previously.
- Moisture or corrosion bridging the contacts or the connector.
How to diagnose it
- Note whether the furnace does nothing at all on a heat call, which fits a pre-start check failing.
- Note recent service history, since a jumpered switch is a real cause.
- Check the Last 6 Faults menu for E3.1 alongside this — both switches shorted at once points at wiring rather than at two failed switches.
- Not a homeowner check.
How to fix it
- Technician work on a safety interlock.
- Wiring should be eliminated before the switch is replaced.
- Any jumper found must be removed and its reason established.
Notes
Two shorted switches reported together are far more likely to be one wiring fault than two coincidental component failures. The fault history menu is what makes that visible.
Related
All codes for this manufacturer
Trane and American Standard furnace flash codes — every code, with what differs between models.
What the fix costs
The paid repair here is the repair guide's pressure switch, $150–400 installed, with two cheaper outcomes worth ruling in first. A short in the second stage switch wiring costs diagnostic time rather than a part, and both stages' switches reading shorted together makes wiring nearly certain — one fault, not two coincidences. The most awkward outcome is the jumper found from earlier service: free to remove, but the reason someone bridged a safety switch has to be established, and that investigation is the real work of the visit.
DIY or call a pro
E3.3 offers the homeowner nothing to fix and one thing to notice: the furnace does nothing at all on a heat call, because this check fails before the inducer starts. That distinguishes it from its open-circuit sibling E3.4, where the furnace still runs on low fire. Report which behaviour you see — a dead-on-arrival heat call fits the shorted switch, a running-but-underpowered furnace does not, and confusing the two sends the diagnosis down the wrong stage. The switch itself is a draft-proving interlock; the cabinet stays closed.
The same fault on other brands
The shorted-switch class spans the industry — per the pressure switch hub, the same defeated interlock appears as Goodman E8, two red on the GMEC96-family board, three blinks on Rheem's *RC controls, and eleven flashes on the Allied -02 control. Those are all single codes for a single switch; a two-stage Trane reporting E3.3 rather than E3.1 is naming which of two switches to test.
What this looks like
From the outside, this usually shows up as the inducer spins up but the burners never fire — that walkthrough covers what to check in order, and when it stops being a homeowner job.