Code
B1518
FIAT
B — Body
Driver seat occupied switch circuit short to ground
Views:
UK: 4
EN: 6
RU: 5
AI status
Completed
Completed
100%
Causes
- Damaged wiring insulation contacting chassis ground (chafing at seat rails or mounting points)
- Corroded or pushed-out connector pins or terminals at the seat switch or module harness
- Faulty driver seat occupied switch (internal short to ground)
- Water ingress/contamination in connector or switch
- Improper aftermarket wiring or accessories (seat heaters, alarms) tied into the circuit
- Internal fault in the control module (input transistor shorted to ground)
Symptoms
- Seat occupied indicator or seatbelt reminder behaves incorrectly (on, off, or intermittent)
- Diagnostic trouble lamp or body control warning set and DTC stored
- Possible constant seatbelt chime or incorrect occupant status reported by scan tool
- In some vehicles, airbag/occupant classification logic may be affected (warnings or inhibited functions)
What to check
- Retrieve freeze frame and live data with a scan tool; note input status for driver seat occupied switch
- Visually inspect seat wiring harness, connectors and switch for damage, corrosion, loose pins and water ingress
- With ignition on, monitor voltage at the seat switch connector pin (at module side and switch side) using a multimeter or scope
- Disconnect the seat switch connector and check if the circuit returns to expected pull-up voltage (indicates short downstream)
- Check continuity between the signal wire and chassis ground (resistance should be high/infinite if healthy)
- Wiggle wiring harness and connectors while monitoring signal to reproduce intermittent faults
Signal parameters
- Typical behavior (generic): switch open = pull-up voltage ~4.5–5V (or module reference voltage); switch closed = ~0V (ground)
- Short-to-ground condition: measured ~0V at signal wire with ignition on
- Open-circuit condition: signal floats to pull-up voltage or shows high resistance; continuity (closed) should read near 0 Ω when switch actuated
Diagnostic algorithm
- Safety: follow manufacturer procedure to disable SRS and remove battery power if required before major seat work
- Connect scan tool and confirm DTC B1518, note freeze frame and live data
- Visually inspect connector and harness under the driver seat for damage, corrosion, or water
- With ignition ON, backprobing at the control module input pin: measure DC voltage. If ~0V, proceed to next steps
- Disconnect the driver seat occupied switch connector at the seat: if voltage now rises to pull-up (≈4.5–5V), the short is in the seat switch or wiring between seat connector and chassis; if still ~0V, the short is toward the module or inside module
- Perform continuity check from the signal wire (at seat connector) to chassis ground. Low resistance indicates a short to ground in harness or components
- Inspect and flex the harness along its full routing (seat rails, seat frame, and B-pillar) while monitoring signal to find intermittent shorts
- If the short is localized to the seat switch, remove/replace the switch or repair damaged wiring/connector pins
- If the wire is shorted along harness, repair or replace wiring and protect with loom/grommets; replace corroded connectors
- If all wiring and switch check good, suspect module internal fault — confirm with module bench test or replacement per manufacturer guidance
- After repairs, clear codes, perform functional test and road test to verify code does not return
Likely causes
- Chafed harness under seat where it rubs on metal components
- Connector under the seat contaminated by moisture or debris
- Damaged switch assembly after seat removal/installation
- Short from a recent service or aftermarket accessory installation
Fault status
Status
B1518 — Driver seat occupied switch circuit short to ground detected. The occupancy input reads continuously low/grounded. Inspect seat switch, harness and connectors for shorts or corrosion; clear DTC after repair.
Repair difficulty: Medium
Diagnostic time: 0.5-2 hours
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