What Does Trane RTU Error Code 91 Mean?
Error Code 91 on many Trane rooftop units indicates a communication failure between the main controller and a connected module or sensor network.
When active, the unit may:
- Show module offline errors
- Disable cooling or heating stages
- Operate in limited fallback mode
Common Causes
- Loose or damaged communication wiring
- Incorrect module addressing
- Failed communication board
- Electrical interference
- Grounding issues
Troubleshooting Steps
- Inspect communication wiring for polarity and continuity
- Verify unique module addresses
- Power cycle affected modules
- Check termination resistors if applicable
Replace control modules only after verifying wiring and addressing.
FAQ
Does this mean the RTU has failed?
No. Most cases involve wiring or configuration issues.