Speed Queen Washer-Extractor Error Code E d 66: Bus Voltage Reading
E d 66 on a CHM1792C washer-extractor is a voltage bus acquisition failure. The drive could not get a valid reading of its internal DC bus voltage, which it needs to run the motor safely. Switch power off to clear it and call us if it returns.
High: the drive cannot read its bus voltage and stops the machine.
- Code
- E d 66
- Maker
- Speed Queen
- Equipment
- Washers
- Applies to
- CHM1792C family washer-extractor (QN models, 20-100 lb) front-end control
What does Speed Queen error code E d 66 mean?
Inside the drive, the DC bus is the internal power line that supplies the motor circuit. The drive measures its voltage constantly, since that number tells it how much power it has available and whether conditions are safe. E d 66 appears when the drive cannot acquire a valid bus voltage reading at all (display text: E d 66). Without that measurement, the drive cannot run the motor safely and so it stops. This is different from E d 21, which means the voltage was measured and found too high. Here the measurement itself failed. Per the owner's manual, powering down clears it. The load stays in the drum while the code shows, until the machine is cleared. The manual lists a voltage reading circuit on the drive board that has failed, supply voltage so unstable that the drive cannot sample the bus, and a loose connector inside the drive wiring. A supply that wanders is a possibility a building electrician can also check.
Affected models and control systems
Speed Queen CHM1792C family washer-extractors (QN models, 20-100 lb) with the front-end control. Other washer-extractor families, such as CHM495R, list different codes.
Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.
What you may notice
- E d 66 on the display
- The machine stops at start or during a cycle
- The load stays wet in the drum
Possible causes
Listed in Speed Queen's documentation
- Voltage reading circuit on the drive board has failed
- Supply voltage so unstable the drive cannot sample the bus
- Loose connector inside the drive wiring
Other likely causes — what usually sits behind error code E d 66 on this control. A technician confirms which one it is before any part is replaced.
- Large equipment on the same feed starting up and dragging the voltage down
- A reading circuit part weakened by repeated voltage swings
Safe checks before calling for service
- Switching the machine off is the owner's manual reset for this code, so start there.
- Let the door lock release by itself.
- Make a note of whether the supply looked unstable, such as lights dimming.
- If the code returns, ask us to visit.
How a technician diagnoses error code E d 66
- Read E d 66 and note whether the building voltage dips when it appears.
- Measure supply voltage at the machine, loaded and unloaded.
- Inspect drive wiring connectors for looseness.
- Check the board for damaged parts in the voltage reading area.
- Replace the drive board once the supply and connectors test good.
- Measuring supply stability means live work at 208-240 V.
- A wandering building supply may need an electrician before the machine is blamed.
- The drive's reading circuit cannot be tested without its specification.
How error code E d 66 differs from similar codes
E d 21 means the bus voltage was measured too high; E d 66 means it could not be measured.
Technical reference
- Document
- Washer-Extractor Programming CHM1792C_SVG, Part No. F8641001ENR4, Error Codes Table 29 (pp. 100-107)
- Edition
- Part No. F8641001ENR4, January 2020
- Models / control
- CHM1792C family washer-extractor (QN models, 20-100 lb) front-end control
- Section
- Error Codes, Table 29, pp. 100-108 (PDF pages equal printed pages)
- Checked
- October 2026
We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.
Related Speed Queen washer error codes
Is E d 66 the same as an over voltage?
No. Over voltage is E d 21; E d 66 means the reading could not be taken.
Could dimming lights be related?
Yes. A shaky supply is one of the listed causes.
Will power-down clear it?
The display clears; the cause remains if it is hardware.
Need help with Speed Queen error code E d 66?
A technician confirms the cause on site and gives you the price in writing before any work starts.