Error Code C2559 is a Cyan TCR (Toner Concentration Ratio) Sensor Adjustment Failure error on Konica Minolta bizhub colour machines. Unlike the C255x density errors that trigger when the sensor reading is outside the normal range, C2559 fires when the machine attempts to run its automatic TCR adjustment routine — a calibration that establishes the correct baseline toner density — and the routine cannot complete successfully. The TCR sensor may be within range, but the adjustment process fails to reach an appropriate value, often due to a degraded developing or imaging unit that has lost the ability to hold correct toner concentration.

C2559 belongs to the C255x TCR sensor adjustment failure family:

• C2559 — Cyan TCR sensor adjustment failure
• C255A — Magenta TCR sensor adjustment failure
• C255B — Yellow TCR sensor adjustment failure
• C255C — Black TCR sensor adjustment failure

C2559 targets the cyan channel specifically. The adjustment routine reports that the machine cannot achieve stable TCR calibration, meaning the toner concentration cannot be adjusted to an appropriate value even though the machine has attempted the procedure the required number of times.

All Affected Models and Exact Component References

C2559 maps to different motor designations, connector paths, and board references depending on the model generation. Always confirm your model first before touching any component.

What Does Error Code C2559 Mean?

The bizhub’s ATDC (Automatic Toner Density Control) system relies on an automatic TCR adjustment routine that runs periodically during warm-up and auto‑stabilisation cycles. This routine functions similarly to a “calibration” for the cyan developer mix — it assesses the current toner‑to‑carrier ratio, then commands the toner supply motor to feed toner into the developing unit until the sensor reading reaches the correct target value. The adjustment routine is designed to maintain consistent colour density and compensate for varying environmental conditions or gradual developer wear.

C2559 fires when this adjustment routine cannot complete successfully. The machine attempts the calibration but cannot achieve a stable TCR reading within the expected range — either because the sensor response is erratic, the developer mix cannot hold the correct toner concentration, or the toner supply path is unable to deliver toner into the developer unit. When the adjustment fails, the machine halts cyan printing to prevent image quality degradation and potential damage to the developer.

On C353, C203‑family (and certain other legacy) models, C2559 can also be triggered by the machine detecting a TC ratio of 4% or less in the developing unit for a given number of consecutive sampling cycles, in addition to failed auto‑adjustment detection. This 4% threshold indicates the cyan toner concentration is dangerously low — a direct indicator that the developer is genuinely under‑toned.

The adjustment failure can be caused by:

• Worn or exhausted cyan imaging/developing unit: Carrier beads past their rated life lose their electrostatic charge capacity and can no longer hold toner properly —‑ the machine attempts to adjust the TCR level but the developer responds sluggishly or not at all. This is the most common cause of persistent C2559 on high‑page‑count machines
• Non‑genuine or incompatible cyan toner: Third‑party toner with incorrect particle size or magnetic/optical properties can prevent the TCR sensor from reading accurately during adjustment —‑ the automatic routine fails because the sensor cannot lock onto the correct target value
• Blocked cyan toner supply path or failed toner motor: Toner is not reaching the developer unit during the adjustment cycle —‑ the machine attempts to add toner but cannot raise the TCR reading enough to complete the adjustment
• Dirty or contaminated TCR sensor window (applicable models): A cyan toner film on the sensor window scatters the optical signal, producing erratic readings that prevent successful adjustment. Specific to C220/C280/C360, C300/C350/C352, C203/C253/C353, and C450/C351/C451 families
• Poor connector contact at FRB CN13/CN14 or cyan imaging unit harness: Intermittent TCR sensor signals cause the adjustment routine to fail intermittently —‑ the machine cannot maintain a stable sensor reading throughout the duration of the calibration cycle

For diagnosis, always first check the consumables status and toner brand, then verify the cyan imaging/developing unit is properly seated. Checking the live TCR reading in service mode confirms whether C2559 is related to a genuine adjustment failure (erratic/fluctuating readings) or an open‑circuit signal (zero reading), directing the entire repair approach.

Common Causes of Error Code C2559

• Worn‑out or end‑of‑life cyan imaging unit / developing unit — the most common cause on high‑page‑count machines. Carrier beads lose their toner‑holding capacity, and the automatic adjustment routine cannot achieve correct calibration even when toner supply is functioning. Always check the consumables counter first
• Cyan imaging unit / developing unit not fully seated — a unit that is slightly unseated has marginal connector contact. The TCR sensor signal becomes intermittent during adjustment, causing the routine to fail. Firmly reinserting the cyan unit resolves many C2559 cases without any parts replacement
• Third‑party or incompatible cyan toner cartridge — compatible toner with incorrect particle size or flow characteristics prevents the TCR sensor from reading accurately during automatic adjustment or causes false readings altogether. Third‑party toners are a documented cause of TCR adjustment failures on all bizhub models
• Empty, near‑empty or blocked cyan toner cartridge — the adjustment routine commands toner supply, but no incoming toner reaches the developer, causing the TCR reading to remain low and the adjustment to fail. Always rule this out by inspecting or replacing the cyan cartridge first
• Blocked cyan toner supply path or bridging — toner bridging (compacted toner blocking the auger path between the cartridge and the sub‑hopper) prevents toner from reaching the developer even when the cartridge is full and the motor is running correctly
• Dirty TCR sensor window (applicable models) — on models where the TCR sensor reads through a window on the imaging unit underside, a cyan toner film on this window produces erratic readings during calibration. Specific to C220/C280/C360, C300/C350/C352, C203/C253/C353, and C450/C351 families
• Failed cyan toner supply motor (M6, M7, M8, M9, M10, M14 per model) — the motor that feeds cyan toner from the cartridge into the developing unit has failed. Toner is not reaching the developer, so the adjustment routine cannot raise the TCR reading to the target level. Check motor operation in service mode
• Faulty FRB or FREYB relay board — the relay board processes cyan TCR signals (and cyan motor control on some models) between the developing unit and the main board. On C224/C284/C364 families and 8‑series models, a failed FRB can cause persistent C2559
• Blown ICP fuses on PRCB (C224/C284/C364 family) — ICP21, ICP40, ICP43, ICP44, ICP46 — inline circuit protectors on the PRCB feed cyan toner supply motor and TCR signal circuits. A blown ICP causes loss of motor power or sensor signal. Always test ICP continuity before replacing the board
• Blown PRCB ICP23 or ICP24 (C654/C754 only) — on these models, ICP23 and ICP24 feed the toner supply motor circuits for all channels. A blown ICP will prevent cyan toner supply, causing adjustment failure
• Faulty PRCB, MFPB, EXCB, CPUB or BASEB — last resort, after all other causes are confirmed and ruled out
• Corrupted NVRAM data — in rare cases, the TCR calibration baseline stored on the PRCB NVRAM becomes corrupted, causing the automatic adjustment routine to fail even with known‑good hardware. If all hardware checks pass but C2559 persists, consider NVRAM initialisation or board replacement

Step‑by‑Step Troubleshooting Procedure

Step 1 — Check the Cyan Toner Cartridge

Always inspect the cyan toner cartridge before any deeper diagnosis. A cartridge that is empty, blocked or incompatible is the simplest cause of C2559 and takes 60 seconds to rule out.

1. Open the toner cartridge access area and remove the cyan cartridge
2. Shake it gently — you should feel and hear toner moving inside. A completely weightless cartridge that produces no movement sound is empty. Even if it feels full, suspect bridging inside the cartridge
3. Check the cartridge outlet seal and toner exit port for blockages — a blocked outlet prevents toner flow even when toner is present inside the bottle
4. If a third‑party cartridge is installed: replace with a fresh genuine Konica Minolta cyan toner cartridge as the very first step. Compatible toners are a documented cause of TCR adjustment failures on all bizhub models
5. After replacing the cartridge (or confirming a known‑good genuine cartridge is installed), close the front door and let the machine run its automatic stabilisation / TCR adjustment cycle. Do not interrupt this cycle — the machine will attempt to clear the error and recalibrate automatically
6. If the error clears, run an ATDC adjustment, then print a few pages with strong cyan coverage (gradients, cyan‑rich test pages) to confirm the new toner has fed into the developer unit
7. If the error persists despite a known‑good genuine cyan cartridge, proceed to Step 2

Step 2 — Check Cyan Imaging Unit / Developing Unit Life (Consumables)

Worn or end‑of‑life cyan units are the most common cause of persistent C2559 on high‑page‑count machines. A unit that cannot hold correct toner concentration will fail the automatic adjustment routine repeatedly.

1. On the machine control panel, navigate to Counter → Consumables (or Utility → Device Status → Consumables, depending on model)
2. Locate the cyan imaging unit (IU/C) or cyan developing unit remaining life percentage
3. If the unit is at or beyond its rated yield (typically 120,000–200,000 pages): replace the cyan imaging unit or developing unit immediately — worn carrier beads cannot hold toner correctly and the adjustment routine will continue to fail. Do not attempt to “force” the adjustment.
4. If the unit is within its life but the error persists, proceed to Step 3
5. Never use a third‑party or refurbished IU/developer unit — the TCR readings and adjustment characteristics are tuned to genuine Konica Minolta developer formulations. Incompatible developer will cause C2559 and may damage the PRCB TCR input circuit

Step 3 — Reinstall the Cyan Imaging Unit or Developing Unit

A unit that is not fully seated is one of the most common and easiest‑to‑fix hardware causes of C2559 across all model families.

1. Power OFF the machine and unplug the power cord
2. Open the front cover
3. Remove the cyan imaging unit (or cyan developing unit on C220/C280/C360 and C224/C284/C364 families) completely
4. Inspect the multi‑pin connector on the back of the unit:
   • Look for cyan toner contamination on the contacts — clean gently with a dry cotton swab or electrical contact cleaner
   • Check for bent, backed‑out or corroded pins
   • On developing‑unit models, also inspect the TCR sensor spring contact for misalignment or corrosion
5. Reinstall the unit firmly and evenly — push until the connector fully engages and the front edge is flush with the machine frame. Confirm any locking mechanism is fully engaged
6. Reconnect power and power on
7. If C2559 clears, run an ATDC adjustment and a test print with strong cyan coverage
8. If the error persists, proceed to Step 4

Step 4 — Clean the Cyan TCR Sensor Window (Applicable Models Only)

On models where the TCR sensor reads through a window on the underside of the imaging unit, a cyan toner film on this window is a common, easily overlooked cause of failed adjustment routines. The contamination scatters the optical signal, producing erratic or false readings.

Applicable to: bizhub C220/C280/C360, C300/C350/C352, C203/C253/C353, C351/C450/C451/C550/C650

1. Remove the cyan imaging unit from the machine
2. Turn the unit over and locate the TCR sensor window on the underside — a small transparent window or opening near the developer roller area that allows the sensor to “see” the developer mix
3. Inspect the window under good lighting — look for a cyan toner film, smear, dust coating or any contamination
4. Clean the window gently with a soft, dry, lint‑free cloth or dry cotton swab. Do not apply liquids — moisture can damage the optical sensor
5. On C220/C280/C360 and C300/C352 specifically: also clean the TCR sensor LED — the emitter that illuminates the developer mix for the optical sensor reading. Clean it with a dry cotton swab
6. Reinstall the unit and power on — a clean sensor window can restore normal TCR readings immediately
7. If the error persists, proceed to Step 5

Step 5 — Check the TCR Reading in Service Mode

Viewing the live TCR sensor reading in service mode is the single most important diagnostic step. It instantly confirms whether C2559 is related to open‑circuit signal loss (connector fault), erratic sensor readings (dirty window or failing unit), or genuine under‑toning that the machine cannot correct.

1. Enter Service Mode and navigate to the developing unit or imaging unit sensor check / ATDC check section (the exact menu path varies by model generation)
2. Observe the live TCR reading for the cyan channel — note the numeric value and any fluctuation or instability
3. Interpret the reading:
   • Reading at or near 0% at cold start: The sensor or its connector is open‑circuit — a full loss of signal. This is always a connector or board fault. The developer concentration is almost certainly normal. Check all connectors in the cyan signal path (Step 6) and replace the imaging/developing unit if the connector is confirmed good
   • Reading consistently below the minimum threshold (4% or less) but above 0%: Genuine low‑density condition — toner starvation is real. Proceed to motor and supply path checks (Step 7). This will prevent any successful adjustment because the machine cannot raise the concentration to the target level even when commanded
   • Reading fluctuates widely or is unstable: Dirty sensor window, failing sensor, or poor connector contact. The adjustment routine cannot lock onto a stable reading. Clean window (Step 4), reseat connectors (Step 6), or replace unit
   • Reading within normal range: The sensor is currently reading correctly. C2559 may have been triggered by a transient condition (e.g., an interrupted adjustment cycle). Run an ATDC adjustment and monitor the machine
4. Run the ATDC adjustment after confirming the toner supply path is working correctly — this recalibrates the sensor baseline and may clear C2559 without further parts replacement
5. If the ATDC adjustment completes without error, print a cyan‑heavy test page to confirm correct density

Step 6 — Reseat All Connectors in the Cyan TCR Signal Path

Use the model‑specific connector references from the table above.

For bizhub C220 / C280 / C360 (FREYB path):

1. Power OFF and unplug the machine
2. Reseat: developing unit → FREYB CN6 (cyan channel connector)
3. Also reseat FREYB CN4, CN8, CN10 (other channel connectors — shared board)
4. Reseat: FREYB CN1 → PRCB CN4
5. Reseat: FREYB CN2 → PRCB CN5

For bizhub C224 / C284 / C364 family / C454 / C554 (FRB path):

1. Power OFF and unplug the machine
2. Reseat: developing unit → FRB CN13 (cyan channel connector) — CN13 = cyan, CN14 = black, CN15 = magenta, CN16 = yellow
3. Reseat: FRB CN1 → PRCB CN7
4. Reseat: FRB CN3 → PRCB CN9

For bizhub C258 / C308 / C368 (8‑series / MFPB path):

1. Reseat: developing unit → FRB CN14 (cyan channel connector on 8‑series)
2. Reseat: FRB CN1 → MFPB CN4E
3. Reseat: FRB CN3 → MFPB CN11E

For bizhub C650i / C550i / C450i:

1. Reseat: developing unit → FRB → EXCB → BASEB — follow full path
2. Check: FRB CN14 (cyan) → MFPB/EXCB connectors

For bizhub 750i:

1. Check connector between developing unit/C — relay CN251 — relay CN248 — EXCB CN6EX
2. Reseat: EXCB CN1EX → BASEB CN11E and EXCB CN2EX → BASEB CN12E

For bizhub C3320i / C3350i / C4050i / C4000i / C3300i (i‑series):

1. Check connector between imaging unit/C → relay CN5 → BASEB CN14E (C3320i/C3350i)
2. Or imaging unit/C → relay CN5 → EXCB CN14E (C4000i/C3300i)
3. Check CPUB for proper installation

Inspect all pins at every connector for bent contacts, toner contamination, and oxidation. Clean contaminated pins with electrical contact cleaner on a cotton swab — allow to dry completely before reconnecting.

Step 7 — Perform Toner Supply Motor Operation Checks in Service Mode

With the imaging/developing unit removed (to prevent toner ejection during the test), verify the cyan toner supply motors respond correctly to drive commands.

For bizhub C220 / C280 / C360 (FREYB):

1. Command M6 (cyan developing): signals at PRCB CN13-12 to 15
2. Command M9 (cyan toner supply): signals at PRCB CN12-13 to 16 (J-10)

For bizhub C224 / C284 / C364 family:

1. Command M10 (cyan toner bottle motor): PRCB CN14-17 to 20
2. Command M7 (cyan toner supply motor): PRCB CN14-9 to 12

For bizhub C258 / C308 / C368 (8‑series / MFPB):

1. Command M10 (cyan toner bottle motor): MFPB CN16E-1 to 4
2. Command M7 (cyan toner supply motor): MFPB CN16E-5 to 8

For bizhub C452 / C552 / C652:

1. Command M10 (cyan developing motor)
2. Command M14 (cyan supply motor)

For bizhub C450 / C451 / C550 / C650:

1. Command M9, M10, M11 (cyan control signals at PRCB CN16)

For bizhub C4000i / C3300i:

1. Command M4, M5: control signals at BASEB CN13E-1 to 4 (M4) and CN13E-5 to 8 (M5)

For bizhub 750i:

1. Command M10, M25, M7, M8, M9: control signals at EXCB CN11EX

Interpreting results:

• Motor runs immediately and smoothly: Motor and drive circuit are functional. Starvation is mechanical — blocked supply path, toner bridging, or failed drive coupling. Proceed to Step 8
• Motor does not respond but drive signal is confirmed present at connector: Motor has failed internally. Replace the motor (Step 9)
• No drive signal at motor connector in service mode: Check ICP continuity (Step 10) before replacing the board

Step 8 — Check and Clean the Cyan Sub‑Hopper / Toner Supply Path

If motors are running correctly but the adjustment still fails, the supply path is likely blocked.

1. Access the cyan sub‑hopper area — typically behind or below the cyan toner cartridge, accessible from the front or right‑side cover depending on the model
2. Inspect the sub‑hopper for toner bridging or clumping — compacted toner blocking the auger path prevents toner from reaching the developer. Break up any clumped toner with a toner‑safe tool and clear the supply path
3. Inspect the toner empty sensor (inside the sub‑hopper) for contamination — cyan toner buildup can trigger false empty readings, suppressing toner supply to the developer even when toner is present in the hopper. Clean gently with a dry cotton swab
4. Check the drive coupling between the cyan toner supply motor and the supply auger — a cracked or stripped coupling will cause the motor to run while no toner movement occurs. Replace the coupling if damaged
5. After clearing any blockage, reinstall the cyan unit and run a motor operation test to confirm toner movement can now occur

Step 9 — Replace the Cyan Imaging Unit or Developing Unit

Replace the cyan unit when:

• The connector is confirmed good, the TCR window is clean, motors are confirmed working, and the TCR reading remains below threshold (or erratic) and the ATDC adjustment repeatedly fails
• The imaging/developing unit page count is at or past its rated life (typically 120,000–200,000 pages) and the carrier beads are degraded
• The TCR sensor is confirmed failed on a developing‑unit model (direct sensor test shows no response or unstable readings)
• You have ruled out toner, connections, motor, supply path, and board — the unit is the only remaining variable

1. Order the correct cyan imaging unit or developing unit for your specific model — OEM only. Third‑party or refurbished units are a known cause of persistent adjustment failures and may not be compatible with the ATDC calibration routine
2. Power OFF and unplug the machine
3. Remove the old unit and install the replacement
4. Navigate to Service Mode → Counter and reset the Imaging Unit /C counter (or Developing Unit /C counter) to zero
5. Run the ATDC adjustment for the cyan channel immediately after installation
6. Run a gradation adjustment and colour calibration for all channels — a new cyan unit will affect overall colour balance across all four channels
7. Print a full‑colour test print and confirm cyan density is correct across the tonal range

Step 10 — Check PRCB ICP Fuses (When Motor No‑Drive Signal Present)

When the motor operation check shows no drive signal at the motor connector, check the inline circuit protectors before replacing the main board.

For bizhub C224 / C284 / C364 family: check ICP21, ICP40, ICP43, ICP44, ICP46 on the PRCB for continuity — these protect the cyan toner supply motor and TCR signal circuits

For bizhub C654 / C754: check PRCB ICP23 and ICP24 — these protect the toner supply motor circuits

Procedure:

1. Access the relevant board (PRCB for most models, FRB for some) and locate the ICP(s) — refer to the specific service manual for exact component locations
2. Test each ICP for continuity with a multimeter — no continuity confirms the ICP has blown
3. Before replacing the board, confirm the associated toner supply motor is not shorted — a shorted motor winding blows ICPs. Test motor winding resistance with a multimeter before installing a new board to prevent immediate re‑blowing
4. If an ICP is blown and the motor is confirmed good: replace the board

Step 11 — Replace the Cyan Toner Supply or Developing Motor

Replace the cyan toner supply motor when the operation check confirms the drive signal is present at the motor connector but the motor does not respond or responds erratically.

1. Confirm drive signal presence before ordering replacement — a motor that has no signal is a board or ICP issue (Step 10), not a motor issue
2. Power OFF and unplug the machine
3. Note the motor mounting orientation and coupling engagement before removing the old motor
4. Disconnect the harness, remove mounting screws, and extract the motor
5. Install the replacement, confirm the coupling fully engages with the drive gear, and reconnect the harness
6. Run the motor operation check in service mode to confirm the replacement motor responds correctly before reassembling covers

Step 12 — Replace the FRB / FREYB Relay Board (If Applicable)

Replace the FRB or FREYB relay board when all other checks pass but C2559 persists, particularly if multiple adjustment errors appear simultaneously (C2559 + C255A + C255B + C255C).

Applicable models:

• C224 / C284 / C364 family — FRB
• C258 / C308 / C368 / 8‑series — FRB

1. Before replacing, confirm no blown ICPs on the PRCB (primary board) — a blown ICP often points to a shorted FRB or motor
2. Test shorted motor windings before installing a new FRB — a shorted motor will blow the new board immediately
3. After replacement, run motor operation checks and ATDC adjustment

Step 13 — Replace the EXCB, CPUB or BASEB (i‑series / 8‑series / 750i / Latest Models)

On i‑series, 8‑series and latest generation models (C650i/C550i/C450i, C750i, C4050i/C3350i), C2559 can be caused by failure of the EXCB (Expansion Control Board), CPUB (CPU Board) or BASEB (Base Board).

For bizhub 750i:

• EXCB replacement
• CPUB replacement
• BASEB replacement

For bizhub C4000i / C3300i: CPUB, BASEB replacement

For bizhub C3320i / C3350i / C4050i: CPUB, BASEB replacement

Procedure:

1. Check CPUB for proper installation before replacing — a loose CPUB can cause TCR adjustment failure
2. If seated correctly, replace these boards in the following order after all other components are confirmed good: FRB → MFPB/EXCB → CPUB → BASEB
3. After replacement, run ATDC and gradation adjustments

Step 14 — Replace the PRCB, MFPB, PWB‑MC or PWB‑MFPC (Last Resort)

Board replacement is the final step and should only be performed after confirmed‑good imaging unit, confirmed‑good connectors, confirmed motor operation, confirmed‑intact ICPs, and a failed ATDC adjustment still produce C2559.

• PRCB — C220/C280/C360, C224/C284/C364 family, C452/C552/C652, C654/C754, C3320i/C3350i/C4050i/i‑series (PRCB replaced by BASEB), 8‑series (PRCB replaced by MFPB)
• MFPB — C258/C308/C368, C300/C350/C352, C450/C351
• PWB‑MC — C203/C253/C353, C450/C351/C451
• PWB‑MFPC — C450/C351/C451

Quick Reference — Troubleshooting by Symptom

Understanding the C255x TCR Sensor Adjustment Failure Family

C2559 is one of four channel‑specific TCR sensor adjustment failure codes:

• C2559 — Cyan TCR sensor adjustment failure
• C255A — Magenta TCR sensor adjustment failure
• C255B — Yellow TCR sensor adjustment failure
• C255C — Black TCR sensor adjustment failure

Unlike the C2551–C2558 density errors (which trigger when the sensor reading is simply too low or too high), the C2559–C255C adjustment errors indicate that the automatic TCR adjustment routine cannot complete successfully — the machine cannot reach a stable toner density baseline. This is often due to degraded developer (worn carrier beads), toner supply obstruction, or unstable TCR sensor readings.

All four adjustment errors appearing simultaneously (C2559 + C255A + C255B + C255C) points to a shared component — the FRB/FREYB relay board, the relay board → PRCB/MFPB connector, the shared PRCB ICP that powers all four motor and TCR circuits, or a common bus between the boards. Do not replace four imaging units for four simultaneous adjustment errors — check the shared electrical path first.

On the C353 · C203‑family (and certain other legacy) models, the detection condition includes TC ratio of 4% or less for a given number of consecutive sampling cycles — this condition also triggers C2559 independently of the automatic adjustment routine. On these models, a TCR reading ≤4% will generate the same C2559 error even if the automatic adjustment procedure has not been invoked. This reflects a direct low‑density detection that the machine equates with an adjustment failure because the concentration is too low to calibrate

On i‑series, 8‑series and latest generation models, C2559 is triggered exclusively by failure of the automatic TCR adjustment routine — the machine attempts to calibrate but cannot achieve a stable reading, often due to worn developer units or erratic sensor signals

Preventing C2559 From Recurring

• Use only genuine Konica Minolta cyan toner cartridges — third‑party toners with incorrect particle size and flow characteristics are a recurring cause of TCR adjustment failures on all bizhub models. Third‑party formulations can also permanently damage the developer mix
• Replace imaging and developing units on schedule — most units are rated for 120,000–200,000 pages. Running past the rated life degrades the carrier bead charge capacity, making the automatic TCR adjustment routine increasingly unreliable. Persistent C2559 on high‑page‑count machines is almost always a worn unit
• Clean the TCR sensor window during every PM on applicable models — on C220/C280/C360, C300/C352, C450/C351, and C203/C253/C353, this takes one minute and prevents the toner film buildup that causes erratic TCR readings and adjustment failures
• Clean the cyan sub‑hopper toner empty sensor and supply path during every PM — contamination here develops slowly over high page counts and is the primary progressive cause of genuine toner starvation that prevents the adjustment routine from completing
• Run ATDC adjustment after every imaging unit or developing unit replacement — the most commonly skipped post‑replacement step. Without recalibration, the ATDC system operates with an incorrect baseline and C2559 may return even after a correct repair
• Reseat the cyan imaging/developing unit connector and FRB CN13/CN14 during PM visits — toner dust accumulates on the connector contacts progressively. A 30‑second reseat and inspection during maintenance prevents the gradual contact degradation that causes intermittent C2559 events between planned service visits
• Never run developer initialisation or attempt to “force” TCR values — the automatic TCR adjustment routine exists for a reason. Attempting to manually force TCR values into a developer unit that is worn or contaminated will not correct the underlying problem and may permanently damage the developer or the PRCB

Professional Technician Summary

Error Code C2559 on Konica Minolta bizhub machines is a cyan TCR sensor adjustment failure. The machine cannot complete its automatic calibration routine to establish a correct toner density baseline. Unlike density errors (C2551–C2558), which trigger when the sensor reading is simply low or high, C2559 indicates that the adjustment routine itself fails — the machine tries to calibrate but cannot reach a stable reading. Unlike many error codes that point to a single failed component, C2559 is most often a systemic failure of the cyan imaging/developing unit, not a peripheral issue like a connector or motor. The overwhelming majority of persistent C2559 cases on high‑page‑count machines are resolved by replacing the cyan imaging or developing unit, regardless of what other tests may suggest.

A common trap is to suspect the PRCB or MFPB too early. The hallmark of C2559 not yet resolved by a new cyan unit is multiple adjustment errors appearing together — C2559 + C255A + C255B + C255C — which indicates a shared component failure (FRB, common ICP, or shared bus) rather than a channel‑specific issue. Also, any C2559 accompanied by visible cyan image degradation (faint output, uneven density, background fog) is almost certainly a genuine low‑density condition (real starvation) even if the TCR reading shows normal — the adjustment routine cannot compensate because the developer is physically unable to hold the required toner concentration. A new cyan unit will resolve both the image quality and the error.

Before opening any covers: always check the cyan consumables counter, confirm the machine is using a genuine Konica Minolta cyan toner cartridge, and reinstall the cyan imaging or developing unit to reseat its connector. These simple preliminary checks resolve C2559 in under two minutes on a significant percentage of office machines.

If the error persists, enter Service Mode, view the live cyan TCR reading. If the reading is at or near zero at cold start, suspect an open‑circuit sensor connector — not developer failure — and focus on connectors.

Always run an ATDC adjustment after correcting any toner supply or sensor issue. This step recalibrates the density system to the corrected state and prevents C2559 from returning due to an uncalibrated baseline — it is the step most frequently skipped after C2559 repairs and the most common cause of the error recurring shortly after a seemingly successful fix.