Trane furnace IdL, Xt1, Xt2, aRF and the other status codes: Normal operation — the display is not showing a fault

This display shows something at all times, not only when there is a fault. Most of what it shows means the furnace is working. Codes beginning with E are faults; these are not.

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

Unlike a single blinking LED, this display is a running status readout. It reports what the furnace is doing right now, and during normal heating it cycles through several values in turn. Trane's published list of normal indications is: IdL for idle with no thermostat demand, Xt1 for first stage heating, Xt2 for second stage heating, aRF for airflow shown as the value times ten so 080 means 800 CFM, C0F for continuous fan, CL1 and CL2 for first and second stage cooling, Xp1 and Xp2 for first and second stage heat pump, and dFt for defrost mode. During a normal first stage heat call the display alternates between Xt1, aRF and the airflow figure — three different readings in sequence, none of them a fault. Someone who opens the panel mid-cycle and writes down whatever the display happened to be showing will often be recording normal operation.

Most common causes

The furnace is running. These indications appear during normal operation by design.
During a simultaneous call for first and second stage heat, Trane notes the display reads Xt2 although the control processes the first stage call first.
The menu system uses further abbreviations — err for the active alarm menu, L6F for the last six faults, Cr for the code release number — which are menu labels rather than status or faults.

How to diagnose it

Check whether the code begins with E. If it does not, it is not a fault.
If the display is cycling between several values, that is normal running rather than a fault sequence.
To look for actual faults, use the L6F menu, which holds the last six. That is the reliable way to see what has gone wrong rather than what is happening now.
aRF followed by a number is an airflow reading, not a code. Multiply by ten for CFM.

How to fix it

Nothing. These indications mean the furnace is operating.
If the furnace is genuinely not heating while showing a status code, use the L6F fault history rather than reading the live display.

Notes

To clear the stored fault list, hold the Option button on the L6F menu for five seconds — three dashes appear three times to confirm. Worth knowing before clearing it, because the history is often the most useful diagnostic information the furnace holds.

All codes for this manufacturer

Trane and American Standard furnace flash codes — every code, with what differs between models.

Sources

Trane Installer's Guide 18-CE01D1-1E-EN — S9V2 two-stage condensing variable speed furnaces, Integrated Furnace Control Display Codes and Fault Code Recovery

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.