Goodman GMVC960803BN Error Code EC4: Equipment Relay Module Missing
What Does Code EC4 Mean?
Error code EC4 on the Goodman GMVC960803BN indicates that the integrated control module has been configured to work with an external equipment relay module but cannot detect that module on the ComfortNet network. The equipment relay module is an accessory component that provides additional control relay outputs for connected HVAC equipment such as a heat pump, air conditioner, or other system components.
This code typically appears when the furnace was previously commissioned with an equipment relay module installed and that module is no longer present — for example, if it was removed during service, if it has failed and dropped off the network, or if there is a wiring problem preventing communication. It can also appear if the system was configured to expect this module but it was never installed.
A technician must determine whether the equipment relay module should be present based on the system configuration, verify its wiring, and either restore the connection to the existing module or install a replacement. If the module is intentionally absent and the system does not require it, the configuration may need to be updated to match the current installation.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Equipment relay module not installed or disconnected | Most common | ✗ Call a pro → |
| Faulty equipment relay module | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- EC4 is present — a technician must verify whether an equipment relay module is required for this system's configuration and either restore communication to it or install one
- The module was removed during service — it must be reinstalled and properly wired before EC4 will clear
✓ Verified against manufacturer service manual — March 2026