B1904: Air Bag Crash Sensor #2 Feed/Return Circuit Failure
What does B1904 mean?
B1904 is a diagnostic trouble code indicating "Air Bag Crash Sensor #2 Feed/Return Circuit Failure". A sensor in the restraint system is reporting abnormal data or has lost communication with the ECU. Sensors can fail due to age, contamination, heat exposure, or wiring issues.
Symptoms you may notice
- Check engine light (MIL) illuminated on dashboard
- Intermittent warning lights
- Erratic gauge readings
Estimated repair cost
Typical range in Australia (parts + labour)
Common causes
- Faulty restraint system component
- Wiring or connector issue in the related circuit
- Failed sensor providing incorrect readings
- Software/calibration issue requiring ECU update
- Related component causing secondary fault
What should you do?
This code sits in the occupant restraint system. The airbags or pretensioners may not fire in a crash, and on some faults they can fire when they should not. The car will usually drive and feel completely normal, which is exactly why this one gets ignored. Have it diagnosed before you carry passengers, and do not clear the code to make the light go away.
Get a diagnosis for YOUR car
Code B1904 can mean different things depending on your vehicle. TorqueBot gives you a diagnosis specific to your make, model, and year.