Code
B2704
HUMMER
B — Body
Passenger presence sensor circuit malfunction
AI status
Completed
Completed
100%
Causes
- Damaged or disconnected passenger presence sensor (seat mat)
- Corroded, bent or loose connector pins at the sensor or module
- Wiring open, short to ground, or short to battery in the sensor circuit
- Water/moisture intrusion into the seat or connector
- Aftermarket seat covers, foam or heaters interfering with sensor operation
- Faulty restraint control module (SDM/RCM) or internal circuitry
Symptoms
- Passenger airbag warning lamp or SRS indicator illuminated
- Passenger airbag enable/disable indicator may read incorrectly or change state intermittently
- Possible airbag system message on instrument cluster or infotainment display
- Fault code B2704 stored in body/restraint control module
- Passenger presence/live data inconsistent or out-of-range (sensor indicates no occupant when occupied or vice versa)
What to check
- Scan vehicle with an appropriate scan tool; record B2704 plus any related codes and freeze frame data
- Verify current state of passenger presence indicator while a known-weight passenger sits in the seat
- Visually inspect passenger seat area: connectors, wiring harness routing, signs of water, corrosion, rodent damage or chafing
- Check for aftermarket seat covers, heaters or recent seat/foam repairs
- With ignition on, check for loose connector(s) under the passenger seat and secure seating connectors
- Use scan tool to view live data from the passenger presence sensor (occupant detected, sensor resistance/weight equivalent, signal voltage) and watch while performing a wiggle test on harness/connector
Signal parameters
- Reference supply typically a stable reference voltage from the restraint module (commonly 5 V) — measure at sensor connector pins
- Signal circuit: voltage varies with occupancy (typical 0–5 V signal range) or resistance changes for mat-type sensors — compare live values to known-good or OEM specification
- Ground continuity: low-impedance ground required at sensor module connector
- Live-data output may be presented as a weight/occupant classification or sensor resistance/voltage in the scan tool
Diagnostic algorithm
- Retrieve and record all codes and freeze frame data with a scan tool; note any related SRS/body codes.
- Confirm symptom: with ignition on, verify passenger presence indicator behavior with a seated test subject (or OEM test weight) and capture live-data values.
- Perform a visual inspection of the passenger seat: connectors, harness routing, signs of moisture, corrosion, or physical damage; remove any aftermarket covers.
- With ignition on and using the scan tool, observe live data while gently wiggling the harness and connectors under the seat to try to reproduce the fault or change live readings.
- Power/ground check: verify reference voltage and ground at the sensor connector per OEM procedure. Do not short circuits; follow safety instructions for SRS circuits.
- Signal check: measure sensor signal voltage or resistance at the connector and compare to OEM acceptance ranges or a known-good seat if available.
- Continuity check: with battery disconnected per safety procedure, check continuity of suspect wiring between sensor and restraint control module; repair any opens/shorts.
- If wiring and connectors are good but sensor output is out-of-range, replace the passenger presence sensor mat assembly per manufacturer instructions.
- After repair, clear codes and perform operational test (with occupant or test weight) to confirm proper sensor behavior and that the B2704 code does not return.
- If sensor and wiring verify good and fault persists, follow OEM diagnostic flow for restraint control module testing and replacement as a last step.
Likely causes
- Wiring connector under passenger seat disconnected, corroded or contaminated
- Damaged seat sensor mat (wear, puncture, moisture)
- Short or open in harness between passenger presence sensor and restraint control module
- Aftermarket seat cover or heated seat element altering sensor readings
Fault status
Status
Passenger presence sensor circuit malfunction. May disable/alter passenger airbag operation. Service required.
Repair difficulty: Medium
Diagnostic time: 0.5-2.5 hours
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