How do you fix Goodman b6?

Replace a restrictive filter and open closed registers, which addresses the airflow contribution to overheating. Supply voltage problems need an electrician, not a heating technician — the furnace is reporting a fault it did not cause. Full steps and safety notes are on this page.

Goodman furnace b6: Blower motor over or under voltage trip, or over temperature trip

b6 means the motor shut down because its supply voltage went outside the acceptable range, or because it got too hot. Two of these three causes are outside the furnace entirely.

Applies to: Goodman GMVC96, GMVM97, GCVC96, GCVM97 and Amana AMVC96, AMVM97 series gas furnaces with a variable-speed ECM blower motor and a two-character display.

What it means

The motor's electronics monitor their own supply voltage and temperature and stop the motor if either goes out of bounds. That groups three quite different situations under one code. Over and under voltage are supply problems — the furnace is being fed electricity outside the range the motor tolerates, which is a house wiring or utility issue rather than a furnace fault. Over temperature is usually about airflow and ambient conditions around the motor. The practical value of knowing this is that two thirds of the causes are not the furnace's fault, and replacing furnace parts will not address them.

Most common causes

Supply voltage low, which can be a utility problem, an undersized circuit, or a loose connection.
Supply voltage high, less common but produced by some generator and utility conditions.
A loose or corroded connection in the furnace's high voltage supply, causing voltage to sag under load.
The motor overheating because airflow is restricted, so it is working hard and being cooled poorly.
High ambient temperature in the furnace space — a hot attic or a confined closet.
A failing motor control module misreading its own conditions.
Operating from a generator with poor voltage regulation.

How to diagnose it

Note whether other appliances in the house show voltage symptoms — lights dimming when large loads start is a useful clue.
Note whether the fault correlates with weather. Over temperature faults cluster in hot conditions, particularly in attic installations.
Note whether the furnace has been running on a generator, which is a common and easily forgotten cause.
Check the air filter and registers, since restricted airflow contributes to the over temperature half of this code.
Note whether the fault appeared after electrical work in the house.

How to fix it

Replace a restrictive filter and open closed registers, which addresses the airflow contribution to overheating.
Supply voltage problems need an electrician, not a heating technician — the furnace is reporting a fault it did not cause.
Have the furnace's high voltage connections checked for tightness if voltage sags under load.
Improve ventilation in the furnace space if ambient temperature is the issue, particularly in attic installations.
Do not have the motor replaced before the supply has been checked. A new motor in the same electrical conditions will trip in the same way.

Notes

This is the furnace code most likely to be reporting a problem elsewhere in the building. A technician who checks supply voltage before condemning the motor saves the cost of an expensive part that was never faulty.

All codes for this manufacturer

Goodman and Amana furnace fault codes — every code, with what differs between models.

Models this code appears on

From the manufacturer's per-model database. If your model is not listed, this code may not exist on your board, or it may mean something different — check the model page.

What the fix costs

Two of this code's three triggers put the money outside the furnace, which changes who you call before it changes what you pay. Supply voltage sagging or spiking is a house-wiring or utility matter — an electrician's visit, or a call to the power company if neighbours see it too — and the furnace side of it may cost nothing once the supply is corrected. Overtemperature usually traces to airflow starving the motor of its own cooling: filter and register fixes are free, duct questions are measured ones. Only a motor actually damaged by those conditions reaches the blower motor cost guide at $900–1,500+ for these variable-speed units — and a motor replaced without the voltage or airflow cause being found inherits the same environment that killed the first one.

DIY or call a pro?

The homeowner evidence here is unusually valuable: do lights dim when big appliances start, did the code follow a storm or a brownout, is the neighbourhood's power flaky? That history separates the electrician's version of b6 from the HVAC version before anyone rolls a truck. The filter check is yours as always, since a smothered motor runs hot. The measurements are not — verifying supply voltage at the furnace and motor temperature behaviour is instrument work on live equipment. One caution: repeated voltage trips are the furnace telling you its electrical diet is bad, and ignoring that can eventually cost board money too, not just motor money.

What this looks like

From the outside, this usually shows up as the blower runs when it should not — that walkthrough covers what to check in order, and when it stops being a homeowner job.

This can also show up as a new or worsening noise from the furnace — that page matches the sound to the likely cause.

Sources

Goodman Manufacturing — Diagnostic Code Identification System (model-specific fault code lookup)

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.