JACK C4 / E4 Overlock Machine Error Codes: Complete Guide

Quick Answer

JACK’s E4 and E4S overlock machines run on the “C4” control box, and it shows its own error codes separate from JACK’s lockstitch machines. JACK’s official operation manual documents 11 codes — E1 through E7, plus EA, Eb, EC, and Ed. JACK’s own official maintenance videos also reference a newer, expanded numbered series (Error 01 through at least Error 26) used on updated C4 boards. This guide covers both, sourced directly from JACK’s official C4/E4 operation manual and JACK Technology’s own “Quickservice” maintenance video series.

What Is the JACK C4 Control Box?

C4 is the control box fitted to JACK’s E4 and E4S power-saving overlock (serger) machines — a different product line entirely from the F4/F5/F6 direct-drive lockstitch range and the A4/K4 auto-trimmer range. Because it runs a four- or five-thread overlock stitch rather than a single-needle lockstitch, its control box watches a different set of motor and sensor conditions, which is why its error codes don’t match either of JACK’s other schemes.

If your machine is a JACK E4 or E4S overlock and its panel shows a code, it almost certainly belongs to the list below rather than the F4/F5/F6 or A4/K4 guides.

JACK C4/E4 Error Code Chart (Official Manual)

Newer C4 Boards: The Extended Error 01–26 Series

JACK’s own official “Quickservice” maintenance video series (published by JACK Technology Co., Ltd) documents additional numbered fault codes on updated C4 control boards, beyond what’s in the original operation manual above. These appear on newer C4 boards as straight numbers rather than letter-plus-digit codes:

If your C4 machine is showing a numbered code above that isn’t a simple restart-and-recheck fix, treat it the same way you would the equivalent lettered code — check plugs and connections first, then the power supply, and call a technician for anything that keeps recurring after that.

JACK C4/E4 Error Codes Explained One by One

E1 — Motor Stuck

E1 means the control box tried to drive the motor and met more resistance than expected. Turn the looper shaft or hand wheel by hand first to check for a mechanical jam — thread wrapped around a looper is the most common cause on an overlock machine. If it turns freely, reduce the load, check the motor plug, and restart.

E2 — Motor Controller Abnormal

E2 shows up when the motor draws more current than expected for a sustained stretch, usually from fabric that’s too heavy for the setup or a machine overdue for lubrication. Power off, wait a few minutes, and restart. Check oil level and fabric weight if it recurs.

E3 — Parameter Save Abnormal

E3 points to the control box failing to save its parameter settings correctly. Restart the machine, or hold the reset button for 3 seconds to force a reset. Contact your dealer if the fault doesn’t clear after a reset.

E4 — Motor Hall Signal Abnormal

E4 means the motor’s Hall sensor signal has gone abnormal — inspect the 10-core connector cable and the Hall sensor wiring for looseness or damage before restarting. JACK’s own official maintenance video for the E4 machine covers exactly this fault.

E5 — Needle Position Signal Abnormal

E5 points to the needle-position sensor rather than the main drive motor. Rotate the hand wheel by hand, restart the machine, and check that the positioner connector is fully seated. If your machine doesn’t need precise needle positioning, this function can be disabled by a technician.

E6 — Speed Governor Abnormal

E6 means the control box isn’t getting a recognizable signal from the speed governor (pedal/speed controller). Check the plug connection and inspect the coder wire for damage; replace the governor if reseating doesn’t help.

E7 — Current Detection Circuit Fault

E7 points to the control box’s own current-sensing circuitry. Clean the circuit board of dust and lint, check that the power voltage is stable, and restart. This is a board-level fault rather than something fixable by cleaning a plug alone.

EA, Eb, EC & Ed — Over-Current, Voltage, and Brake Faults

These four are all power-supply and braking-circuit protections: EA is a hardware over-current trip, Eb is system over-voltage, EC is system under-voltage, and Ed is a brake resistor protection fault. For Eb and EC, cut power immediately and check that your supply matches the rated 220V rather than continuing to restart the machine repeatedly.

A Different Family: JACK JK-T781E Bartack/Pattern Machines

If your machine is a JACK electronic pattern or bartack machine (the JK-T781E series), it uses yet another distinct control system, with its own six documented codes: E1 (power module error / abnormal over-current or over-voltage), E3 (stepper motor communication abnormal), E6 (stepper motor sensing abnormal), E7 (loose plug, position signal fault, blocked head, or heavy fabric), E9 (positioning signal abnormal), and E11 (needle signal can’t output at startup — often a faulty positioner inside the control box). These share some letter-codes with the C4/E4 overlock scheme above, but the meanings are different machine-to-machine, so match the code to your actual model family before troubleshooting.

Maintenance Tips to Prevent Repeat Faults

• Clean thread lint and dust out of the looper area regularly — overlock machines accumulate lint far faster than lockstitch machines, and it’s a common trigger for E1/E2-type faults
• Reseat the motor, Hall sensor, and positioner plugs during routine servicing
• Keep the machine oiled on schedule to avoid overload-type faults
• Use a voltage stabilizer if your mains supply fluctuates, to cut down on repeat Eb/EC trips

Genuine Spare Parts for JACK Overlock Fixes

We stock the control boards and sensors behind most of the faults above:

• Direct Drive Servo Motor Control Board — for board-level E7/EA/Eb/EC faults
• JACK Wire Connector — fixes intermittent E1/E4 connection faults
• JACK Wheel Sensor — fixes recurring E5 needle-position faults

Frequently Asked Questions About JACK C4/E4 Overlock Error Codes

What does E1 mean on a JACK overlock machine?

E1 on a JACK C4/E4 overlock means the motor is stuck or under heavier load than expected. Check for thread jams in the loopers first, then reduce load and check the motor plug.

Is the JACK overlock E4 code the same as the JACK F4 lockstitch E4 code?

They’re conceptually similar — both point to an abnormal motor Hall signal — but they run on different control boxes (C4 for overlock, F-series for lockstitch), so the wiring and parts you check are specific to your machine type.

My JACK overlock control box shows a numbered code like “Error 09” instead of a letter code — what does that mean?

Newer C4 control boards display an expanded numbered series documented in JACK’s own official maintenance videos — Error 09, for example, means an abnormal pedal connection. Check the corresponding numbered table above.

Related guides: JACK F4/F5/F6 Error Codes Guide | JACK A4/K4/A5 Error Codes Guide | JACK vs Juki Buying Guide

Written by Aashu, owner of Stitch Partner. We source genuine JACK spare parts every week — this guide is cross-checked against JACK’s own C4/E4 operation manual and JACK Technology’s official maintenance video series.