B118C

Code

Generic B — Body

Occupant Classification Sensor Communication Fault

Brand: Generic

Type: B — Body

Views: UK: 5 EN: 16 RU: 6

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged or disconnected wiring harness to occupant classification sensor
Corroded or loose seat cushion/seat module connectors
Faulty occupant classification sensor module or sensor mat (weight/pressure sensors)
Faulty restraint control module (RCM) or BCM communication circuit
Software/firmware mismatch or calibration fault
Intermittent connection due to seat movement or foreign objects in connector

Symptoms

SRS/Airbag warning lamp illuminated
Passenger airbag disabled or not deployable (message on dash 'Passenger Airbag OFF')
Inaccurate occupant detection (system shows wrong weight/empty/occupied)
DTC B118C stored in SRS/BCM memory
Intermittent warning or lamp that comes on after seat movement

What to check

Read and record all stored SRS/BCM/Sensor codes with a capable scan tool; check freeze frame and related codes
Visual inspection of seat connectors, sensor mat plugs, and harness routing for damage, corrosion or water
Check for TSBs or required calibrations/software updates for occupant classification system
Wiggle-test harness and connectors while watching live data to reproduce communication fault
Verify proper battery voltage and good ground connections before testing SRS circuits

Signal parameters

Sensor supply/reference voltage typically present (check for ~5 V reference or manufacturer-specified value)
Ground continuity between sensor module ground and chassis ground
Data/bus activity on CAN or LIN lines (messages from OCS/seat module visible on scan tool)
OCS live-data values should change smoothly with applied weight; no erratic spikes or dropped messages
Connector pin voltages and resistance of sensor mat circuits should match manufacturer service values

Diagnostic algorithm

Use a qualified scan tool to read codes from SRS, BCM and seat/OCS module. Note related codes and freeze-frame data.
Inspect connectors at the seat cushion, seat frame and the OCS module. Unplug, inspect terminals for corrosion, bent pins, or foreign debris, then securely reconnect.
With battery connected, monitor live data for the OCS while moving seat and applied weight. Perform a wiggle test on harness and connectors to attempt to reproduce the fault.
Verify power and ground at the sensor connector with key ON. If reference or ground is missing, trace and repair wiring to source (fuse, BCM, ground point).
Check communication bus (CAN/LIN) for errors. Verify other modules on bus communicate and inspect termination resistors if needed.
If wiring and connectors are good, measure sensor mat resistances or voltages per manufacturer procedure. Replace sensor mat/module if values are out of spec or data is absent.
If replacement or repair performed, clear codes and perform any required occupant classification calibration or initialization procedure with scan tool.
Verify repair by confirming codes do not return and that occupant detection and SRS lamp behave correctly after road test/verification.

Likely causes

Corroded/loose connector at seat cushion or seat frame
Broken or pinched wires in seat harness (common at seat rail/hinge)
Failed occupant classification sensor module or sensor mat
Loss of reference voltage or ground to sensor
Bus communication error between OCS module and RCM (CAN/LIN fault)

Fault status

⚠️ Status

Occupant Classification Sensor communication fault detected — module not responding, reporting invalid data, or communication interrupted. SRS lamp illuminated and passenger airbag status may be altered.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1.0 - 2.5 hours