Code
B2772
HUMMER
B — Body
Occupant Classification System Sensor Input Fault
AI status
Completed
Completed
100%
Causes
- Damaged or contaminated occupant classification sensor mat (seat cushion sensor)
- Corroded, loose, pinched or disconnected connector under the seat
- Harness short to ground or power, open circuit, or intermittent wiring
- Faulty occupant classification module/sensor electronics
- Water/moisture intrusion into seat or sensor area
- Incorrectly installed/aftermarket seat cover or seat heater interfering with sensor
Symptoms
- Airbag / SRS warning lamp illuminated on dash
- Message or indicator showing passenger airbag disabled/enabled unexpectedly
- Passenger airbag may not deploy when occupied or may not be able to be turned off
- Stored DTC B2772 (may accompany other B27xx codes)
- Possible seat belt reminder or other restraint system warnings
What to check
- Read DTCs and freeze frame with a capable scan tool; record related SIR/OCS codes
- Visual inspection of passenger seat area for moisture, damage, or aftermarket covers
- Inspect and reseat connectors under the passenger seat; look for corrosion, bent pins, or foreign material
- Check wiring continuity and for shorts/opens between sensor mat and OCC module (follow wiring diagram)
- Verify reference supply and signal at sensor connector with key ON (per service manual)
- Confirm whether occupant classification system requires a calibration procedure after repairs
Signal parameters
- Reference supply typically provided by restraint control module (often 5 V reference) — verify exact value from service manual
- Sensor output may be a variable voltage/resistance or digital data depending on model; expected change between empty and occupied states
- Expect stable, plausible signal with key ON — look for open (no signal), short to ground/power, or noisy/intermittent values
- Module communication may use a dedicated OCC bus or be integrated on SIR network — check for communication errors with scan tool
- Compare measured resistance/voltage values to manufacturer specifications before replacing parts
Diagnostic algorithm
- Safety first: follow manufacturer procedure to disable the SIR system (disconnect battery and wait specified time) before working on seat or connectors.
- Use a scan tool to confirm B2772 and note any accompanying codes or freeze-frame data.
- Visually inspect the passenger seat, sensor mat, connectors, and harness for damage, contamination, or water ingress.
- With SIR disabled per manual, unplug and inspect the seat/OCS connectors for corrosion, pushed pins, or foreign debris; reconnect and verify secure fit.
- Restore power and, using a scan tool and multimeter, check reference voltage and sensor signal at the connector with the seat empty and with a known weight per the service manual to observe expected change.
- If signal is open/short or does not change, perform harness continuity and short-to-power/ground tests between connector and restraint control module.
- If wiring and connectors are good but sensor signals remain invalid, remove the seat cushion to visually inspect or bench-test the sensor mat per service procedures; replace mat if faulty.
- If sensor mat replacement is performed, follow calibration/programming procedures required by the manufacturer for occupant classification system recalibration.
- Clear codes and perform functional verification with scan tool and by confirming correct passenger airbag status under known occupancy conditions.
- If fault persists after verifying sensors and wiring, consider replacement of the occupant classification module or module reprogramming per dealer procedures.
Likely causes
- Connector under passenger seat is loose/corroded or pins bent
- Seat cushion sensor mat damaged due to impact, wear, or liquid spill
- Wiring harness chafed where it passes through seat tracks or under the carpet
- Module or sensor electronics failure
- Calibration data invalid after seat removal or repair
Fault status
Status
Stored when the occupant classification sensor input is out-of-range, open/shorted, invalid, or otherwise not providing expected data to the restraint control module; may disable or incorrectly enable the passenger airbag.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Repair manuals
Manual library for HUMMER
138
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