Code
B1515
FIAT
B — Body
Driver seat occupied switch circuit
Views:
UK: 4
EN: 8
RU: 4
AI status
Completed
Completed
100%
Causes
- Open circuit in seat occupied switch wiring (broken wire, disconnected connector)
- Short to ground or battery in switch circuit
- Corroded, loose or damaged connector at seat switch or module
- Failed seat occupied switch or sensor (pressure mat, mechanical switch)
- Faulty body control module (BCM) or occupant detection module
- Water intrusion or contamination in seat connector or sensor
Symptoms
- DTC B1515 stored and MIL or warning lamp may be illuminated
- Occupant detection warnings or incorrect passenger/driver airbag status
- Seatbelt reminder/indicator behaving incorrectly for driver
- Occasional or constant failure to detect occupant presence
- Possible disabling of SRS airbag or safety features for that seating position
What to check
- Retrieve freeze frame and live data with a scan tool to view seat occupied signal status and fault history
- Visual inspection of seat, connectors and wiring under the seat for damage, corrosion, water or loose plugs
- Wiggle test wiring while monitoring live data to reproduce intermittent faults
- Measure voltage at the seat occupied switch connector with ignition on (see signal parameters)
- Check continuity and resistance of switch circuit with connectors disconnected (power off) to detect open or short
- Confirm proper vehicle grounding and battery voltage levels
Signal parameters
- Type: discrete switch or sensor input to BCM/occupant detection module
- Expected voltages: near 0 V (ground) when switch closed/occupied; near battery voltage (~10–14 V) when open/unoccupied (vehicle specific)
- Expected resistances: closed condition ≈ 0–5 Ω (short/low resistance); open condition typically >10 kΩ or infinite (open circuit)
- Signal behavior: stable steady state while occupied/unoccupied; intermittent or oscillating values indicate wiring or connector issues
Diagnostic algorithm
- Read and record DTCs and live data with a capable scan tool. Note freeze-frame and any related codes (airbag/BCM).
- Perform a visual inspection of the seat area: connectors, harness routing, clips, seat frame chafe points, and evidence of liquid contamination.
- Disable the battery and follow manufacturer SRS safety procedures before accessing under-seat components.
- With ignition ON (and following safety steps), backprobe the seat occupied switch connector and verify signal voltage states (occupied vs unoccupied) per signal parameters.
- If voltage is incorrect or intermittent, remove the connector and inspect pins for corrosion, bent pins, or damage. Repair or replace connector/terminals as needed.
- Check continuity of the switch circuit between the BCM/occupant module connector and the seat switch. Repair any open or short circuits found.
- If wiring and connectors are good, verify switch/sensor operation by testing resistance across the sensor while applying weight/pressure (compare open vs closed resistance). Replace sensor/mat if out of specification.
- After repairs, clear codes and retest system. Verify proper stable live data and that the DTC does not return in normal operation.
- If fault persists and wiring/sensor tests good, consider BCM/occupant detection module diagnostic/repair or reflash per manufacturer procedures.
Likely causes
- Poor connector pin contact at seat harness
- Wiring chafe under seat causing intermittent open/short
- Failed pressure/occupancy mat or switch
- Corrosion from spilled liquids or moisture
- Incorrectly installed or incompatible replacement seat/parts
Fault status
Status
Driver seat occupied switch circuit fault — open/short or intermittent signal detected between seat occupancy sensor/switch and vehicle control module.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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