B1516

Code

FIAT B — Body

Driver seat occupied switch circuit open

Brand: FIAT

Type: B — Body

Views: UK: 20 EN: 24 RU: 24

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Page language: EN

Causes

Broken or disconnected wiring in the driver seat occupancy switch circuit
Corroded, bent or loose connector pins at the seat switch or control module
Faulty driver seat occupied switch or sensor assembly
Poor or missing ground for the seat sensor circuit
Faulty body control module / occupant detection module
Water ingress or physical damage to seat wiring harness

Symptoms

Airbag or SRS warning lamp illuminated
Seatbelt reminder or 'occupant detection' message displayed incorrectly
Passenger/driver airbag may be incorrectly enabled/disabled
Seat- or belt-related systems not behaving as expected
DTC B1516 stored in memory

What to check

Retrieve and record freeze frame data and any other stored DTCs with a compatible scan tool
Perform a visual inspection of the driver seat wiring, connectors, and seat base for damage or corrosion
Backprobe the seat occupied switch connector and check for expected reference voltage and switch signal while changing seat occupancy
Check continuity between the switch connector and the body/SRS control module connector with connectors disconnected
Wiggle test the harness while monitoring the signal to see if the fault is intermittent
Inspect grounds related to the seat sensor circuit

Signal parameters

Switch type: normally open/closed or resistive weight sensor — design varies by model
Typical behavior: open circuit (infinite Ω) when unoccupied, measurable continuity or return voltage when occupied — exact voltages depend on vehicle design
Common voltages: 0 V (ground) or reference voltage (often 5 V) returned to module when occupied; may also be a low-voltage logic signal (0–5 V)
Resistance: closed switch/seat-occupied state generally shows low resistance; unoccupied shows very high or infinite resistance
If uncertain, consult the vehicle wiring diagram and module data for exact reference voltages and expected signal states

Diagnostic algorithm

Use a factory-level or compatible scan tool. Read and record B1516 and any related codes; note freeze frame.
Follow safety procedures for SRS work: disable battery and wait the manufacturer-specified time before disconnecting SRS connectors (consult service manual).
With ignition ON (and SRS safety steps observed), visually inspect the driver seat connectors, wiring at the seat base, and any harness routing through the door sill for chafing or damage.
Backprobe the seat occupied switch connector. With a multimeter, check for reference voltage at the supply wire and the switch signal behavior while sitting on and leaving the seat (or actuating the switch).
If the signal is open or absent, disconnect connectors and check continuity between the switch and the module connector; repair any open circuits found.
Inspect and clean connector pins; repair corroded or damaged terminals with appropriate tools or replace the connector assembly.
If wiring and connectors test good, measure the resistance of the seat occupied switch itself. Replace the switch/sensor assembly if it shows open circuit when it should be closed.
If the switch and wiring are good but the module does not see the correct signal, consider module input fault — confirm with wiring diagram and, if possible, swap/replace module or consult dealer-level diagnostics.
After repairs, clear codes with the scanner and perform a functional test and short road or operation test to confirm the fault does not return.

Likely causes

Open or disconnected connector at the driver seat occupied switch
Broken wire inside the seat harness (wear at seat base or belt pretensioner area)
Failed seat switch/weight sensor
Corroded pins in the seat wiring connector
Module input circuit fault (less common)

Fault status

⚠️ Status

Driver seat occupied switch circuit open — open circuit detected in the driver seat occupancy sensor circuit. May trigger SRS/airbag or seatbelt warnings and affect passive restraint operation.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours

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