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Home / DTC / B1540 — OCSS control unit

B1540 — OCSS control unit

Detailed page for trouble code B1540.

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Code

B1540

MITSUBISHI B — Body

OCSS control unit

Brand: MITSUBISHI
Type: B — Body
Views: UK: 22 EN: 20 RU: 22
AI status
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Page language: EN

Causes

  • Internal failure of OCSS control unit/module
  • Open, short or high-resistance wiring in sensor harness (seat mat)
  • Poor connector contacts or corrosion at seat or control unit connectors
  • Loss of power or ground to OCSS module (blown fuse, poor ground)
  • CAN / LIN / SRS bus communication fault between OCSS and airbag ECU
  • Water intrusion or physical damage to seat sensor mat or module

Symptoms

  • SRS / airbag warning lamp illuminated on instrument cluster
  • Passenger airbag enable/disable lamp incorrect or not responding
  • Passenger airbag may be disabled or automatic disable not working
  • Related SRS DTCs present in diagnostic memory
  • Possible inability to complete occupant classification calibration or learn procedure

What to check

  • Safety first: consult vehicle service manual for SRS procedures. Disable battery and wait specified time before touching SRS components.
  • Use a capable diagnostic scanner to read and record all SRS-related codes and freeze-frame data.
  • Visually inspect seat area, occupant sensor mat, connector pins and OCSS module for corrosion, damage, or water ingress.
  • Inspect and verify in-line fuses and power/ground connections to OCSS module.
  • With battery connected and ignition ON, check for additional SRS/CAN communication codes and live data from OCSS (if supported by scan tool).
  • Wiggle test seat wiring and connectors while monitoring live data to detect intermittent faults.

Signal parameters

  • Power supply (ignition ON): ~battery voltage (approx. 11–14 V) at OCSS power pin
  • Ground: near 0 V; low continuity (
  • CAN bus idle voltages: around 2.5 V on CAN High/Low (differential signalling) — verify with OEM reference
  • OCSS sensor outputs: variable based on occupant detection; consult factory live-data values and expected ranges
  • Resistance of occupant sensor mat and harness: refer to vehicle-specific service manual for acceptable values

Diagnostic algorithm

  1. Safety: Disable battery negative terminal and follow manufacturer wait time for SRS capacitors before proceeding.
  2. Scan and record all SRS codes (including pending). Note freeze frame and related codes.
  3. Visually inspect passenger seat area, OCSS connector and harness for damage, contamination or water ingress.
  4. Reconnect battery, turn ignition ON (do not start). Using scan tool, monitor live data from OCSS and SRS ECU; perform a wiggle test on harness/connectors to reproduce fault.
  5. Verify power and ground at the OCSS connector with a DVOM. If power/ground are out of range, trace and repair supply/ground circuit (fuse, wiring, ground point).
  6. Check CAN/SRS communication: verify bus voltages and presence of OCSS messages. Repair CAN wiring or connectors as needed.
  7. Measure seat sensor mat/harness resistance per service manual. Replace mat or repair damaged wiring if out of specification.
  8. If wiring and power/ground/communication are good and the fault persists, consider replacing OCSS control unit/module per OEM procedure.
  9. After repair or module replacement, perform required initialization/calibration (occupant sensor learn procedure) and clear codes. Verify that codes do not return and SRS light is off.
  10. If problem persists after above, consult manufacturer technical service information or escalate to dealer-level SRS specialist.

Likely causes

  • Damaged or corroded connector at passenger seat OCSS module
  • Open/short in seat occupant sensor mat wiring under the seat
  • Faulty OCSS control unit (internal electronics)
  • Poor ground under seat or disconnected power fuse to OCSS
  • Intermittent CAN/SRS bus connection or short to battery/ground

Fault status

⚠️ Status
OCSS control unit malfunction — check occupant classification sensor, wiring, power/ground and communication with SRS ECU.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0 - 3.0 hours

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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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