UniMac Washer-Extractor Error Code E d 66: Bus Voltage Reading Missing
E d 66 means the drive board on a UniMac QN washer-extractor could not read the DC bus voltage feeding the motor. Take the washer off power, wait, and try once. If it happens again, call us with the time E d 66 showed.
High: without a bus reading the drive cannot protect itself or the motor, so the cycle stops.
- Code
- E d 66
- Maker
- UniMac
- Equipment
- Industrial laundry
- Applies to
- CHM1792C family washer-extractor (QN models, 20-100 lb) front-end control
What does UniMac error code E d 66 mean?
A UniMac QN washer-extractor such as the UCA020QN reports E d 66 when its drive board fails to acquire a bus voltage reading. The bus is the DC voltage inside the drive from which the motor is powered. The drive reads it constantly, since the motor can be controlled and protected only if that number is known. When the reading cannot be taken, the drive has nothing to judge by and stops the cycle.
Notice that the code says nothing about the voltage being too high or too low. It says the number could not be read. That points to the sensing circuit rather than to the power itself. A failed bus voltage sensing circuit on the drive board is the leading cause. A loose or corroded connector on the board can interrupt the reading. Unstable supply voltage may disturb it. A board that cannot read bus voltage needs replacing.
Power cycling clears the display, but the underlying board problem can come back.
Affected models and control systems
E d 66 is listed for the CHM1792C family washer-extractors, the QN models from 20 to 100 lb, with the front-end control and drive board; the manual's example model is the UCA020QN.
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
- The display shows E d 66 and the cycle stops
- The code clears after a power-down but returns
- No drum movement while the code is up
- Other drive codes may appear in the same week
Possible causes
Listed in UniMac's documentation
- A failed bus voltage sensing circuit on the drive board
- A loose or corroded connector on the drive board
- Unstable supply voltage that disturbs the bus voltage reading
- A drive board that cannot read bus voltage and needs replacing
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.
- Voltage divider resistor on the drive board drifted out of tolerance
- Chemical vapor corrosion on the sensing connector pins
- Brief supply dips at start-up while the bus is charging
- Ground wire to the drive board loose, giving a floating reading
Safe checks before calling for service
- Following the maker's operator step, take the washer off power to clear the message.
- Give it a moment, then power up and try once.
- Do not open panels.
- If it happens again, call us with the time E d 66 showed.
How a technician diagnoses error code E d 66
- Read the code and check whether E d 21 or other bus codes preceded it.
- Measure incoming supply voltage at start-up and during a cycle.
- Inspect the drive board connectors for corrosion and looseness.
- Compare the actual bus voltage with what the drive reports, if the board allows it.
- Replace the drive board when the reading is missing on a stable supply.
- Checking bus voltage means measuring a high DC voltage that stays live after power is removed.
- The sensing circuit is on the drive board and cannot be reached without opening it.
- A new board must match the machine's configuration.
How error code E d 66 differs from similar codes
E d 66 is a missing bus voltage reading, while E d 21 is a bus voltage that was read and found too high.
Technical reference
- Document
- Washer-Extractor Programming CHM1792C_SVG, Part No. F8641001ENR4, Error Codes Table 29 (pp. 100-107)
- Maker documentation
- UniMac owner support
- 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 UniMac industrial laundry error codes
Is the voltage too high or too low?
Neither. The code only says the drive could not read the bus voltage.
Will restarting solve it?
It clears the display, and the washer may run for a while. A problem in the sensing circuit tends to return.
Can I watch for a pattern?
Yes. Noting the time and cycle step each time helps us find whether it follows supply dips.
Need help with UniMac error code E d 66?
A technician confirms the cause on site and gives you the price in writing before any work starts.