Lennox E117 Error Code — What It Means
E117 on a Lennox furnace indicates a poor ground has been detected by the integrated control. Lennox classifies this as a warning only, not a hard lockout. The code clears automatically about 30 seconds after the ground fault is corrected. The control has sensed an improper or unstable earth ground path in the furnace system, which can stem from missing equipment ground connections, loose or damaged harness wiring, or control board problems affecting the neutral and ground reference.
Common Causes
- Missing or improper equipment ground The furnace lacks a solid earth ground connection or the grounding conductor is broken or disconnected.
- Loose or damaged harness connections Miswired, corroded, or loose terminals in the harness disrupt the ground path or neutral reference seen by the control.
- No 120 V present at L1 and neutral Loss of line voltage at the integrated control points to an upstream supply or control board issue.
- Integrated control board fault A failing control board may not detect proper voltage even when the supply and ground are intact.
- Broken or open wiring in the harness Damaged conductors inside the wiring harness create intermittent or complete ground reference loss.
Step-by-Step Fix
- {‘lead’: ‘Verify equipment grounding’, ‘text’: ‘Inspect the furnace cabinet and confirm a continuous earth ground connection from the unit to the building ground system.’}
- {‘lead’: ‘Measure 120 V across L1 and neutral’, ‘text’: ‘Use a multimeter at the integrated control terminals to confirm line voltage is present.’}
- {‘lead’: ‘Inspect the harness if voltage is present’, ‘text’: ‘Examine all harness connectors, terminals, and wiring for loose pins, corrosion, open conductors, or physical damage.’}
- {‘lead’: ‘Troubleshoot the integrated control if voltage is absent’, ‘text’: ‘Trace back to the power supply circuit and test the control board for internal faults if no line voltage appears at the board.’}
- {‘lead’: ‘Repair or replace the faulty component’, ‘text’: ‘Secure loose ground or harness connections, replace damaged wiring, or install a new integrated control as needed.’}
- {‘lead’: ‘Restore power and monitor the code’, ‘text’: ‘Power up the furnace and confirm E117 clears within 30 seconds once the ground fault is corrected.’}
Parts Often Needed
| Part | Notes |
|---|---|
| Integrated control board | Amazon | Replace if line voltage is absent at the board or internal fault is confirmed. |
| Wiring harness | Amazon | Replace if conductors are damaged, terminals are loose, or opens exist in the harness. |
| Ground wire or grounding lug | Amazon | Install or repair if equipment ground is missing or disconnected. |
When to Call a Pro
Call a licensed HVAC technician if you are uncomfortable working with 120-volt AC line power, if you cannot confirm voltage readings at the integrated control, or if the fault persists after verifying grounding and harness connections. Ground and neutral faults can create safety hazards and require proper diagnostic equipment and knowledge of electrical codes. A technician will measure voltages, inspect all connections under power, and determine whether the control board or harness requires replacement.