Goodman GMEC960803BN Error Code Red 9 Flashes: Grounding or Reversed Polarity
What Does Code Red 9 Flashes Mean?
Nine red flashes on the Goodman GMEC960803BN control board indicate that the 115-volt power supply to the furnace has reversed polarity or improper grounding. The control board checks that the hot wire (L1) measures approximately 115 volts to ground and that the neutral wire measures 0 volts to ground. If these readings are reversed, the furnace will not operate.
The most common cause is the hot and neutral wires being swapped at the furnace disconnect, the circuit breaker panel, or at an outlet if the furnace is cord-connected. This can happen after electrical work, a panel upgrade, or if the furnace was recently installed or moved.
Improper grounding — such as a missing, broken, or loose ground wire — can also trigger this code. The control board relies on a solid earth ground reference to accurately detect polarity. Without proper grounding, the voltage readings become unreliable and the board may flag a polarity error even if the hot and neutral are correctly wired.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| 115V hot and neutral wires reversed | Most common | ✗ Call a pro → |
| Missing or improper ground connection | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The furnace shows 9 red flashes and will not operate
- You suspect the electrical wiring was recently modified
- The furnace was recently installed or relocated
✓ Verified against manufacturer service manual — March 2026