B2644

Code

Generic B — Body

Front Passenger Occupant Detection Sensor Circuit Malfunction

Brand: Generic

Type: B — Body

Views: UK: 12 EN: 9 RU: 12

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Page language: EN

Causes

Open, short to ground, or short to battery in occupant sensor wiring
Faulty occupant detection (seat weight/occupancy) sensor or mat
Poor connector contact, corrosion, or bent pins at sensor or ECU
Water/moisture intrusion into seat cushion or sensor assembly
Blown fuse or power/ground supply failure to sensor circuit
Faulty airbag/restraint control module or internal driver circuit

Symptoms

Illuminated airbag/SRS warning lamp on instrument cluster
Passenger airbag status (ON/OFF) may be incorrect or disabled
Possible inability of restraint system to correctly classify passenger
Diagnostic trouble code(s) stored in SRS/airbag control module

What to check

Read and record DTC(s) and freeze-frame data with a capable scan tool
Visual inspection of passenger seat, connectors, and wiring for damage or corrosion
Check relevant fuses and power/ground circuits for the SRS/passenger sensor
Backprobe sensor connector and monitor live signal while operating seat or placing weight on seat
Wiggle test wiring and connectors while monitoring live data for intermittent changes

Signal parameters

Reference/specified supply: typically a low-voltage reference (commonly 5 V) — confirm with factory service data
Signal: usually a low-voltage analog/switch signal that changes with occupancy (expected to vary between near 0 V and several volts) — check manufacturer values
Resistance: occupant detection mats may show a specified resistance range or change when weight applied — measure against service manual
Continuity: no open circuit between sensor connector and restraint control module harness pin
Communication: some systems report occupancy over the SRS module bus; verify expected message presence with scan tool

Diagnostic algorithm

Connect a diagnostic scan tool capable of reading SRS/occupant classification data. Confirm B2644 and any related codes; record freeze-frame and current live data.
Perform a careful visual inspection of the passenger seat area, underside of cushion, and connector boots for signs of water, corrosion, connector damage, or foreign objects.
Verify fuses and check for correct power and ground at the SRS control module and at the occupant sensor connector with the ignition in the required position.
Backprobe the sensor connector and monitor the occupant sensor signal while the seat is unoccupied and while applying weight (use a known weight or have a technician sit in the seat). Compare behavior to expected changes; watch for intermittent or no-change conditions.
Measure continuity and resistance of the sensor circuit (with battery disconnected as required). Look for opens, shorts to ground or battery, and abnormal resistance. Wiggle the wiring harness and seat rails to reproduce intermittency.
If wiring and connectors are good, disconnect the sensor and measure sensor-specific resistances/voltages per manufacturer data. If out of spec, replace the sensor/mat assembly.
If sensor measures within spec but code remains, inspect and test the SRS module connector and harness to the module. Consult wiring diagrams to trace the circuit; repair any harness damage.
After repairs, clear codes with the scan tool and perform operational tests (monitor live data, confirm passenger airbag status toggles appropriately). Retest to ensure the code does not return.
If intermittent and no wiring fault found, consider replacement of the sensor assembly before replacing the SRS module; if multiple modules/sensors fail diagnostics, consult vehicle manufacturer technical service information.