Code
B1148
HUMMER
B — Body
Passenger Presence Sensor Circuit Malfunction
AI status
Completed
Completed
100%
Causes
- Open circuit or short in passenger presence sensor wiring (open, short to ground, short to battery)
- Corroded, loose or damaged connector at sensor, harness or module
- Faulty passenger presence sensor (seat mat/pad or load cell)
- Faulty Occupant Classification Module (OCM) or SRS control module
- Water intrusion or contamination in seat cushion or connector
- Recent seat replacement, repair or improper reinstallation (pinched wires, incorrect connector)
Symptoms
- SRS/Airbag warning lamp illuminated on instrument panel
- Passenger airbag may be disabled or displays 'OFF' incorrectly
- DTC B1148 (and possibly other occupant classification codes) stored in SRS module
- Passenger detection behaves inconsistently (seat occupied but system shows empty)
- Difficulty completing Occupant Classification System calibration or learn procedures
What to check
- Connect a suitable scan tool and read all SRS/occupant classification codes and freeze-frame data
- Visually inspect passenger seat, trim, connectors and wiring for damage, corrosion or water contamination
- Check for recent repairs or seat removal that could have disturbed harness routing or connectors
- Wiggle test wiring and connectors while monitoring diagnostic data for intermittent changes
- Confirm vehicle battery voltage is stable before performing voltage checks
- Follow manufacturer procedure to disable SRS before removing trim or disconnecting connectors (disconnect battery and wait specified time)
Signal parameters
- Reference voltage to sensor circuit typically supplied by SRS/OCM — usually a regulated 5 V reference (verify exact value in service manual)
- Signal voltage from sensor varies with occupant presence — expected range 0–5 V (varies by design); refer to service manual for thresholds
- Open-circuit = infinite/OL on ohmmeter or no signal voltage at connector
- Short-to-ground indicated by near 0 V at signal or very low resistance to ground (
- Short-to-battery indicated by signal ~battery voltage with ignition on
- Resistance of seat mat/pad varies by design; consult service manual for exact ohm values
Diagnostic algorithm
- Retrieve all SRS/occupant classification DTCs with a qualified scan tool; record freeze-frame and live data. Check for related codes.
- Follow safety procedure: turn ignition off, disconnect negative battery terminal and wait manufacturer-specified time (commonly 2–10 minutes) to disable SRS capacitors before accessing connectors.
- Visually inspect passenger seat cushions, seat track area, and seatback for water, damage, or foreign objects. Inspect connectors under the seat for corrosion, bent pins, or loose locking tabs.
- Reconnect battery (if removed for inspection) and backprobe the sensor connector with the scan tool monitoring live data. With ignition ON (engine off), verify reference voltage present at the connector (typically ~5 V).
- Measure signal voltage while the seat is unloaded and while a known weight is placed on seat (use appropriate test weight per service manual). Verify signal changes and stays within expected range.
- With ignition off and battery disconnected, perform resistance/continuity checks of sensor element and wiring: check for open circuits, short to ground, and short to battery between sensor pins and SRS module connector. Compare to service manual expected values.
- Wiggle the wiring harness and connectors while monitoring live data for intermittent faults. Pay attention to wires routed through seat rails and hinges.
- If wiring and connector checks are good but sensor signal is out of range or inconsistent, replace the passenger presence sensor (seat mat/module) per manufacturer instructions.
- If sensor and harness are good, suspect OCM/SRS module fault — follow module-level diagnostics; avoid replacing module before confirming wiring and sensor integrity.
- After repair or replacement, clear DTCs, perform required Occupant Classification System (OCS) calibration/relearn per manufacturer procedure, then verify proper operation and absence of codes.
- If problem persists or intermittent and difficult to reproduce, consult manufacturer technical service bulletins and consider module bench diagnostics or dealer-level support.
Likely causes
- Damaged or corroded seat connector or wiring harness (common cause)
- Failed seat mat or pressure sensor element due to wear or moisture
- Intermittent open/short caused by seat movement or damaged cable under the seat
- Fault in Occupant Classification Module when wiring and sensor test good
Fault status
Status
Passenger Presence Sensor Circuit Malfunction stored by the Occupant Classification/Restraint module. The fault can cause the passenger airbag to be disabled or trigger the SRS warning lamp. Further electrical and sensor checks required.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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