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Home / DTC / B1558 — OCSS control unit

B1558 — OCSS control unit

Detailed page for trouble code B1558.

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Code

B1558

MITSUBISHI B — Body

OCSS control unit

Brand: MITSUBISHI
Type: B — Body
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Poor power supply or blown fuse to the OCSS control unit
  • Corroded, loose or damaged connector(s) at the OCSS unit or seat sensors
  • Open or shorted wiring between seat sensors, OCSS control unit and airbag/SRS ECU
  • Water intrusion or physical damage to seat sensor mat or control module
  • Intermittent or failed communication on vehicle network (CAN/LIN)
  • Internal failure of the OCSS control unit (electronic fault)

Symptoms

  • SRS/Airbag warning lamp illuminated
  • Passenger airbag enabled/disabled indicator abnormal or incorrect
  • Diagnostic trouble code B1558 stored in vehicle memory
  • Possible disablement of passenger airbag or incorrect deployment behavior
  • Intermittent warning lamp or codes returning after clearing

What to check

  • Retrieve all SRS and body codes with a capable scan tool; record freeze frame/data
  • Visual inspection of seat area, connectors under the seat and OCSS module for corrosion, moisture or damage
  • Inspect and verify fuses and power supply to the OCSS control unit
  • Wiggle test wiring harness while observing live data for intermittent changes
  • Check continuity and resistance of sensor circuits and harness to chassis/airbag ECU
  • Verify CAN/LIN communication to the OCSS module with a scope or scan tool

Signal parameters

  • Module supply voltage (ignition ON): typically ~11–14 V (verify against vehicle spec)
  • Ground: low resistance to chassis (expected
  • Seat sensor output: variable 0–5 V or sensor resistance values depending on type (compare to vehicle spec)
  • CAN bus idle voltages: CAN_H ~2.5–3.5 V, CAN_L ~1.5–2.5 V (verify continuity and bus activity)
  • Communication: valid periodic messages from OCSS shown on scan tool (message frequency per vehicle spec)

Diagnostic algorithm

  1. Safety first: disable battery negative connection and follow manufacturer procedures for SRS service before working near seats or airbags.
  2. Connect an appropriate SRS-capable diagnostic scanner; read and record all fault codes and live data related to OCSS and SRS.
  3. Clear codes and re-run to confirm B1558 returns; note if code is permanent or intermittent.
  4. Perform visual inspection of the OCSS control unit, seat sensor mat, and all related connectors for corrosion, water ingress, damage or loose pins.
  5. With ignition ON (and safety precautions), measure module supply and ground voltages at the OCSS connector; compare to expected ranges.
  6. Check continuity and resistance of sensor circuits and harness to the SRS ECU; look for opens/shorts or high resistance.
  7. Monitor live sensor values and OCSS messages on the scan tool while performing wiggle tests and while sitting on the seat to confirm correct change of occupancy data.
  8. Verify CAN/LIN network integrity: check bus voltages, message presence and error frames. Repair any wiring/connector issues found.
  9. If wiring, connectors and sensor mats are good but fault persists, follow manufacturer procedure to test or replace the OCSS control unit. Reprogram or initialize module if required.
  10. After repairs, clear codes and perform a functional test and road test per manufacturer SRS protocols to confirm fault does not return.

Likely causes

  • Connector pin corrosion or bent pins at the seat module
  • Broken harness under the seat (pinch/wear from seat movement)
  • Low battery or poor battery connection causing undervoltage to module
  • Seat occupancy sensor mat failure or shorted sensor elements
  • SRS/airbag ECU not receiving valid occupancy data due to module fault

Fault status

⚠️ Status
OCSS control unit malfunction detected — verify power, ground, wiring/connectors, seat sensor integrity and communication with SRS ECU.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

B1550 B1559 B1540 B1600 B1620 U0424
406

Browse 406 MITSUBISHI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

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