Code
B2858
HUMMER
B — Body
Occupant Classification System (OCS) Sensor Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Damaged or disconnected seat occupant sensor connector(s)
- Corroded or bent connector pins under the passenger seat
- Broken, chafed, or shorted wiring harness between sensor and OCS module/airbag control module
- Faulty OCS sensor mat / load cell array in the seat cushion
- Water intrusion / liquid damage in seat cushion or connector
- Aftermarket seat covers or modifications interfering with sensor operation
Symptoms
- SRS / airbag warning lamp illuminated on instrument cluster
- Passenger airbag disabled or unexpected 'Airbag Off' message
- Instrument cluster message advising occupant classification system fault
- Occupant detection behavior incorrect (airbag not enabling for a seated passenger or enabling for empty seat)
- Possible inability to communicate with OCS module when scanned
What to check
- Read and record all related SRS/OCS DTCs and freeze frame data with a capable scan tool
- Visually inspect passenger seat, connectors, and wiring harness under the seat for damage, corrosion, or moisture
- Verify seat rails are not pinching or chafing the harness; wiggle the seat while monitoring live data / DTC status
- Check connector pins for bent/pushed-back pins and for corrosion; reseat connectors
- Measure reference voltage and ground at the sensor connector with key ON (see signal_params)
- Measure sensor signal output while varying seat load (careful: do not damage airbag components)
Signal parameters
- Sensor reference: typically a regulated reference (approx. 5 V) supplied to the sensor circuit — verify per model service manual
- Sensor output: expected to vary with load; typically within ~0.5–4.5 V under normal loading conditions (model-specific)
- Open circuit: infinite resistance / no output signal
- Short to ground: signal near 0 V
- Short to battery/5V supply: signal near reference voltage
- Exact resistance or voltage ranges are manufacturer-specific — consult the HUMMER service manual for target values
Diagnostic algorithm
- Retrieve and record all SRS/OCS codes and freeze-frame data. Note whether code is permanent or intermittent.
- Inspect passenger seat area, connectors, and wiring for obvious damage, moisture, or aftermarket seat covers. Repair any physical damage.
- With the connector exposed, verify the presence of reference voltage and a good ground at the sensor connector with key ON, engine OFF. Compare to manufacturer spec.
- Monitor live OCS sensor data with a scan tool while applying known weight or sitting in the passenger seat (use safe procedures). Look for proper signal changes and check for intermittent behavior when moving the seat.
- Perform continuity and resistance checks between the sensor connector and the airbag/OCS module connector to find opens or shorts. Wiggle harness and seat while observing for changes.
- If wiring and connectors are good but signal out of spec, test or replace the seat sensor mat/load cells per service procedure, or replace the sensor harness if damaged.
- If sensor and wiring test good, verify OCS module/airbag control unit operation and perform module-level diagnostics or replacement only after confirming harness and sensor integrity.
- After repairs, clear DTCs, perform any required OCS recalibration/relearn procedures, then verify the fault does not return and confirm correct passenger airbag status.
Likely causes
- Open or intermittent connector under the seat (common due to seat movement)
- Wiring abrasion on seat rail causing intermittent short to chassis or power
- Corrosion/water damage to the sensor mat
- Sensor mat failure (age or physical damage)
- Disconnected harness after seat service or replacement
Fault status
Status
Occupant Classification System sensor circuit malfunction detected for passenger seat. The OCS sensor signal is out of expected range, open, shorted, or not communicating. Inspect sensor mat, connectors, wiring, and module before repair.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
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138
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