Goodman furnace E6: Flame signal is too weak
E6 means the furnace is lighting and running, but the control can barely detect the flame. It is a warning ahead of a failure — the furnace still heats, and before long it will not.
Applies to: Goodman GMVC96, GMVM97, GCVC96, GCVM97 and Amana AMVC96, AMVM97 series gas furnaces with a two-character alphanumeric display.
What it means
Flame detection works by rectification: the control applies a small voltage to the flame sensor and reads the tiny current that flows through the flame itself, measured in microamps. E6 means that current is above zero but low enough for the control to flag it. That makes this an unusual and genuinely useful code — a predictive fault rather than a failure. The furnace is still working while it is displayed. Left alone, the signal keeps falling until it drops below the threshold, at which point the furnace can no longer prove flame, shuts the gas off, and eventually locks out with E0 instead.
Most common causes
- The flame sensor is coated with oxide or carbon, insulating it from the flame. This is the most common cause by a wide margin.
- The sensor is bent or has shifted so it sits only partly in the flame.
- Poor furnace grounding, since rectification needs a solid ground path.
- A weak or lazy burner flame caused by low gas pressure.
- Restricted combustion air, producing a flame that carries current poorly.
- A cracked ceramic insulator on the sensor, leaking signal to the cabinet.
- Corroded or loose wiring between the sensor and the board.
How to diagnose it
- Note that the furnace is probably still heating. This code often appears while everything seems fine, which is exactly when acting on it is cheapest.
- Check whether the furnace has started short-cycling or occasionally failing to stay lit. That is the signal falling further.
- Check when it was last serviced. A sensor uncleaned for several seasons is the usual explanation.
- Mention any other intermittent electrical oddities to the technician, since poor grounding causes this and several other faults together.
How to fix it
- Book a service call before the furnace fails rather than after. This is the rare code that gives warning, and the repair is usually inexpensive.
- Cleaning a flame sensor is technician work. It sits in the burner flame, in the circuit that decides whether gas keeps flowing, and refitting it wrongly recreates the failure it was meant to fix.
- Have grounding checked at the same visit if the sensor was cleaned recently and the code has come back.
- Low gas pressure needs correcting at the valve or the supply, which is also licensed work.
Notes
A flame sensor is a plain steel rod with a ceramic insulator and no moving parts, and cleaning it takes minutes. Worth knowing, because the alternative outcome is the same repair carried out on the coldest night of the year at emergency rates.