A 2-flash code on a Trane RTRM has many possible causes. Trane’s support article lists 22, including supply fan failure, zone sensor failure, frostat active, smoke detector active and communication failures with the RTOM, RTDM or RTVM. To narrow it down, take four DC voltage readings at RTRM connector J6 and read each one as High, Low or Pulsing.
What a 2-flash on the RTRM covers
The 2-flash code is not a single fault. Trane’s article “What can cause a 2 flash code on the RTRM” lists 22 conditions that can produce it. Many of the listed causes are devices, wiring or conditions outside the module, so replacing the RTRM first skips most of that list. The ones we have confirmed from the article include:
- Supply fan failure.
- Zone sensor failure.
- Manual compressor lockout.
- Outdoor coil sensor failure, on heat pumps.
- Defrost fault.
- Gas heat failure.
- Frostat active.
- Smoke detector active.
- Outdoor air sensor failure.
- Communication failure with the RTOM, RTDM or RTVM.
Some entries apply only to VAV units: the static transducer, high duct static and the discharge air sensor. If your unit is not a VAV unit, those do not apply to it. The full list of 22 is in Trane’s article, and you should work from that list for your unit rather than from this summary.
Several of these are conditions you can see or test without opening the controller. A frostat or a smoke detector that is active is a state of that device. A supply fan that has failed is a fan problem. A manual compressor lockout is a state you can look for. A sensor failure is a sensor, its wiring or its connection. Check these before you consider the controller.
How to pull fail codes at connector J6
Trane’s second article, “How do I retrieve fail codes from the RTRM when I have a 2 flash fault code,” describes a voltage method. You take four DC voltage readings at connector J6 and compare each against Trane’s table. The readings are taken between J6-6 and each of four other terminals:
- J6-6 to J6-7: heat.
- J6-6 to J6-8: cooling.
- J6-6 to J6-9: system status.
- J6-6 to J6-10: service alerts.
For each reading, you record whether the voltage is High, Low or Pulsing, and then look the combination up in Trane’s table. We do not reproduce the table or any voltage values here. Trane’s article is the authority for what each reading means, and a number copied into a different article loses its context. Open the Trane article, keep it next to the meter and read the table from there.
Trane labels the four readings by area: heat, cooling, system status and service alerts. Use the area to decide where to look first, and use Trane’s table for what the reading means in that area. Take all four readings in one pass and write them down before you change anything, so that you compare like with like.
Working through a 2-flash
- Confirm the code. Watch the RTRM LED over several cycles and confirm it is a 2-flash before you act on this article.
- Treat the J6 readings as live-voltage work. The readings are taken on a powered controller. Use a meter rated for the job and have a qualified technician take them.
- Take the four J6 readings. Use the terminal pairs above and write down High, Low or Pulsing for heat, cooling, system status and service alerts.
- Compare against Trane’s table. Read the combination from the Trane article. Do not rely on a table from a different source, since wording differs between publishers.
- Check the visible conditions first. Look at the supply fan, the frostat and the smoke detector, and ask whether the compressor was manually locked out.
- Check sensors and their wiring. For the zone sensor, outdoor air sensor and, on heat pumps, the outdoor coil sensor, check the connection and the wiring before you condemn the sensor.
- Check gas heat and defrost where they apply. Gas heat failure and defrost fault are both on Trane’s list. For gas heat, our ignition board flash codes article covers the ignition side.
- Check the communication modules. If the unit has an RTOM, RTDM or RTVM, confirm communication with the RTRM.
- Rule out the VAV-only items only if your unit is a VAV unit. Otherwise they do not apply.
- Replace the part that the evidence points to, and take the number from that part or your unit’s parts documentation.
Parts involved
Our Trane listings are mainly gas-heat and motor items, and most of the controller items on Trane’s list are not matched to a listing. We describe each row by its title or by the open collection, and we do not claim fit to a specific unit.
| Component | Role in this issue | Where to find it |
|---|---|---|
| RTRM, RTOM, RTDM, RTVM | The module itself, and the modules whose communication failures are on Trane’s list. Not matched to a listing; send the number from the module. | Request a quote |
| Zone, outdoor air and outdoor coil sensors | Sensor failures are on Trane’s list. Sensors and controls are listed under several brands, and none is matched to an RTRM sensor, so search by the number on the sensor. | Controls |
| Supply fan motor | Supply fan failure is on Trane’s list. We list Trane-brand blower motors, described only by title. Confirm by the number on your motor. | Trane X3804031101 Blower Motor 208-230V 50/60 Hz — Replacement |
| Gas heat components | Gas heat failure is on Trane’s list. Pressure switches and inducers for gas heat are listed under the Trane brand. | Trane Replacement Parts |
| Frostat, smoke detector | Both are named as active conditions. Not matched to listings; send the number from the device. | Contact us |
Scope: This article covers the Trane RTRM 2-flash code and the J6 fail-code method as described in the two Trane support articles under Sources. It applies to Trane equipment with an RTRM. It does not cover other Trane codes or other manufacturers’ rooftop controls, and residential furnace code tables do not apply. Check your unit’s own service literature for anything not covered here.
Before you order
Confirm your unit’s exact model and serial number from its nameplate before ordering. Search the part number in our site search, or browse the Trane replacement parts collection. If the number you need is not listed, use our request a quote page, or contact us at help@totalhvacparts.com and we will help confirm fit. Our OEM HVAC parts ordering checklist lists what to have on hand. For economizer-related flash codes, see the RTEM economizer flash codes article.
Frequently Asked Questions
What causes a 2 flash on a Trane RTRM?
Trane lists 22 possible causes, including supply fan failure, zone sensor failure, manual compressor lockout, frostat active, smoke detector active, gas heat failure and communication failures with the RTOM, RTDM or RTVM. Use the J6 voltage readings to narrow it down.
How do I read RTRM fail codes at J6?
Take four DC voltage readings between J6-6 and J6-7 (heat), J6-8 (cooling), J6-9 (system status) and J6-10 (service alerts). Read each as High, Low or Pulsing, then compare with the table in Trane’s support article.
Can an active frostat or smoke detector cause a 2 flash?
Yes. Trane lists both “frostat active” and “smoke detector active” among the causes. Check the state of each device before you suspect the controller.
Do the VAV-only causes apply to every unit?
No. Trane marks some causes as VAV only: the static transducer, high duct static and the discharge air sensor. If your unit is not a VAV unit, work through the other entries.
Sources
- Trane support, “What can cause a 2 flash code on the RTRM?” (22 listed causes)
- Trane support, “How do I retrieve fail codes from the RTRM when I have a 2 flash fault code?” (J6 voltage method and High, Low and Pulsing readings)
Taking readings at the RTRM involves energized control wiring and, in the unit, line-voltage components, rotating equipment and possibly gas heat. Service should be performed only by qualified personnel, following Trane’s service literature for your unit and your facility’s lockout/tagout procedures.