UniMac Washer Error Code Eio 31: Door Lock Pulse Pin
Eio 31 on a UniMac QN washer-extractor means the I/O board found a hardware failure at the door lock solenoid pulse pin, so it may not be able to engage the lock at all. The control stops. Note whether the door would lock, power the machine down with the cabinet closed, and call us.
High: a door that cannot be locked means the machine stops and stays off until tested.
What does UniMac error code Eio 31 mean?
Eio 31 on UniMac QN washer-extractors such as the UCA020QN means the input and output board found a hardware failure at the door lock solenoid pulse pin. The pulse is the short burst the board sends to move the lock into position. The board checks the pin that produces it. If that pin fails its check, the board may not be able to engage the lock at all, and a washer must not run with a door that cannot be locked. The control therefore stops and holds the code. Like the other Eio codes, it comes from the board's own test and says nothing about the door panel. The manual lists a loose connector where the lock output leaves the I/O board, a lock solenoid coil or wire shorted and stressing the pulse output, and a failed pulse driver on the I/O board.
Affected models and control systems
Listed for the CHM1792C family of UniMac QN washer-extractors (20-100 lb), with the UCA020QN as the example model, on the input and output (I/O) board.
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
- Eio 31 on the display and the door will not latch
- No click from the lock at the start of a cycle
- Cycle refuses to start
- Code returns after a restart
Possible causes
Listed in UniMac's documentation
- Loose connector where the lock output leaves the I/O board
- Lock solenoid coil or wire shorted and stressing the pulse output
- Failed pulse driver on the I/O board
Other likely causes — what usually sits behind error code Eio 31 on this control. A technician confirms which one it is before any part is replaced.
- A lock plug backed partly out after the door area was serviced
- A pinched lock wire where it runs to the hinge side
- A pulse driver weakened by repeated lock cycles over years of daily use
Safe checks before calling for service
- Note the code Eio 31 and whether the door would lock at all.
- Power the machine down and keep the cabinet closed.
- Do not try to jam or hold the door shut.
- Call us to test the lock circuit.
- Mention any door noise or play you noticed.
How a technician diagnoses error code Eio 31
- Read the code and test whether the lock pulses when a cycle starts.
- Inspect the lock connector at the board and the harness along its path.
- Measure the lock coil resistance and check for a short to ground.
- Verify the pulse output at the board against the wiring diagram.
- Replace the lock or board only after the tests identify which one fails.
- A lock that cannot engage is a safety issue, so the repair should not be improvised.
- Checking the pulse output is done with a meter on a live board near 208-240 V circuits.
- Telling a shorted coil from a failed driver needs measurement of the circuit under power.
How error code Eio 31 differs from similar codes
Eio 31 is the pulse pin. Eio 30 is the disable pin, and Eio 32 is the relay pin.
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 washer error codes
Does Eio 31 mean the door is broken?
No. It is the board's pulse output that failed its check.
Can I hold the door closed and run?
No. Never hold or jam the door to run a cycle.
What if the code returns each time?
Then the lock circuit or board needs testing, which we do on a visit.
Need help with UniMac error code Eio 31?
A technician confirms the cause on site and gives you the price in writing before any work starts.