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Error code reference

Samsung Multifunction Printer Error Code #04-002

LSU motor does not operate or drive signal is abnormal.

Samsung codesSamsung multifunction printer codes

LSU motor does not operate or drive signal is abnormal.

First step from the service manual

After checking the LSU motor rotation noise, check the motor signal.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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  • Step-by-step tests with expected resistance, voltage, and continuity values
  • Wiring diagram references and connector pinouts from the OEM service manual
  • Verified part numbers when replacement is required
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What #04-002 means on a Samsung multifunction printer

Error code #04-002 on a Samsung multifunction printer indicates a failure in the LSU (Laser Scanning Unit) motor. The LSU motor drives the polygon mirror inside the laser scanning assembly, which is responsible for sweeping the laser beam across the photosensitive drum to form the latent image during printing. When this motor fails to reach its operating speed, stalls, or produces an abnormal drive signal, the printer's control board detects the fault and halts operation, throwing this code.

The diagnostic process begins by listening for LSU motor rotation noise during a print cycle. A functioning LSU motor produces a distinct high-pitched spin-up sound as the polygon mirror accelerates to speed. If no sound is present, the motor itself or its power supply circuit is likely at fault. If sound is present but the error still triggers, the issue shifts toward the motor feedback signal, meaning the control board is not receiving proper confirmation that the motor has reached target RPM. This signal is typically a Hall effect or FG (frequency generator) pulse that the main board monitors.

Common root causes include a seized or worn LSU motor, a faulty LSU motor driver circuit on the main board, a damaged harness connector between the LSU and the main board, or a defective LSU assembly as a whole. Because the LSU is a sealed optical and mechanical unit, internal motor failure usually requires replacing the entire LSU assembly rather than just the motor component.

Source: manufacturer service documentation.

Common causes of #04-002

  1. 01

    Seized or failed LSU polygon mirror motor

    Part replacement

    The motor inside the laser scanning unit has worn out or seized, preventing it from spinning. Listen during power-on for the absence of the normal high-pitched spin-up noise as a key indicator.

  2. 02

    Defective LSU assembly

    Part replacement

    The entire laser scanning unit may be faulty, either mechanically or electronically. Since the LSU motor is not a separately serviceable component in most configurations, a bad LSU unit requires full assembly replacement.

  3. 03

    Damaged or disconnected LSU harness connector

    Wiring / connection

    A loose, corroded, or physically damaged cable connector between the LSU and the main board can interrupt both the motor drive signal and the feedback signal. Inspect the connector and harness for visible damage or poor seating.

  4. 04

    Faulty LSU motor driver circuit on the main board

    Part replacement

    If the harness and LSU check out correctly, the motor driver circuitry on the main control board may be unable to supply the proper drive signal to the motor. This would require main board replacement.

  5. 05

    Intermittent motor signal due to contamination or vibration

    Wiring / connection

    Dust or debris inside the LSU can cause the polygon mirror motor to struggle or produce an erratic feedback signal even if the motor itself is not fully failed. Cleaning the exterior connectors and ensuring secure mounting may resolve marginal cases.

See the test procedure for each cause

Frequently asked questions about #04-002

What does #04-002 mean on a Samsung multifunction_printer?
Error #04-002 means the LSU (Laser Scanning Unit) motor is not operating correctly or its drive signal is abnormal. The LSU motor spins the polygon mirror that steers the laser beam during printing. When the control board cannot confirm that this motor is running at the correct speed, it triggers this fault and stops printing to prevent damage.
Can I fix Samsung error #04-002 myself?
Some basic checks are within reach for a technically inclined user, such as inspecting and reseating the LSU harness connector. However, if the LSU motor itself has failed or the LSU assembly needs replacement, this repair involves handling precision optical components and is best performed by a qualified technician. Improper handling of the LSU can cause additional print quality problems.
Will resetting the printer clear error #04-002?
A simple power cycle or factory reset will not clear error #04-002 if the underlying hardware fault is still present. The printer checks LSU motor operation during every startup sequence, so the error will return immediately if the motor or its signal circuit remains defective. The hardware issue must be resolved before the code will clear permanently.
Is it safe to continue using the printer with error #04-002?
The printer will typically refuse to print while this error is active, which is intentional. Attempting to force operation with a malfunctioning LSU motor could potentially cause additional damage to the laser scanning unit or related components. It is best to leave the printer powered down until the fault is diagnosed and repaired.
How much does it cost to repair Samsung error #04-002?
Repair costs depend on the root cause. If only the harness connector needs reseating or replacement, costs are minimal, typically in the range of $10 to $40 for parts. If the full LSU assembly requires replacement, parts and labor can range from $80 to $250 or more depending on the printer model. Main board replacement, if needed, can push total costs higher, sometimes making repair less economical than replacement for older units.

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