Goodman GMVM970803BN Error Code b6: Blower Over/Under Voltage Trip or Over Temperature Trip

What Does Code b6 Mean?

The variable-speed ECM blower in the GMVM970803BN monitors the 115 VAC line power feeding it and the temperature inside its own power module. If the incoming voltage swings above or below the acceptable range on the furnace rating plate (typically 115 VAC plus or minus 10 percent), or if the power module runs too hot, the motor protects itself by shutting down. The Integrated Control Module reports this as a b6 and the furnace stops.

On this board it is important to read b6 apart from the other blower codes. A b3 is the motor limiting its output while still running, and a b4 is a high-current or lost-rotor trip; a b6 is specifically a voltage or power-module-temperature protection event. It is also not the same as a heat-exchanger overheating code: the over-temperature here is inside the blower motor's own power electronics, whereas the primary high-limit trip from an overheated heat exchanger is an E3 on this furnace. Because the voltage side of b6 often originates in the home's electrical supply rather than the furnace, it frequently needs an electrician as well as an HVAC technician.

The voltage half of this code commonly traces to utility fluctuations, an undersized or shared circuit that sags under load, or loose and corroded connections at the breaker panel or furnace disconnect. The over-temperature half traces to a hot, poorly ventilated blower compartment or a motor forced to overwork against restricted airflow. Both require measurement and electrical work, so this is not a homeowner repair.

What You'll Notice

• The furnace stops running and delivers no heat
• The dual 7-segment display shows b6
• The ComfortNet thermostat shows a Call for Service icon and scrolls Check Furnace
• The shutdowns may coincide with lights dimming or other large appliances cycling on
• The problem may appear during the coldest weather when the system and the home's electrical load are highest

Common Causes

How This Is Diagnosed

A technician (or electrician) first measures the line voltage at the furnace disconnect while the unit is under load and compares it to the rating plate range. Voltage that sags low or spikes high points to the electrical supply, so they check the breaker, disconnect, and wiring connections for loose or corroded contacts that cause voltage drop, and look at whether the furnace shares an overloaded circuit.

If the voltage stays within range, attention shifts to the over-temperature side: the technician checks that the blower compartment has adequate ventilation and clearance, and whether restricted airflow is forcing the motor to overwork and overheat its power module. This isolates whether the root cause is the home's power supply or a thermal condition around the motor. The description here is informational; the measurements and any wiring corrections are technician and electrician work.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The b6 shutdowns coincide with flickering lights or other appliances affecting the furnace, suggesting a home electrical-supply problem
• The code recurs during very cold weather or high electrical load in the house
• The blower compartment or utility space runs hot or is poorly ventilated
• The furnace was recently worked on electrically or is on a shared or undersized circuit

✓ Verified against manufacturer service manual — March 2026