What Does B1904 Mean?
This code indicates the Airbag Control Module (ACM) has detected an electrical fault in the power supply (feed) or ground (return) circuit for crash sensor #2. The sensor is not receiving proper voltage or cannot complete its circuit path, preventing the ACM from monitoring impact data from this specific crash sensor location. This compromises the supplemental restraint system's ability to deploy airbags appropriately in a collision.
Safety Warning
Vehicle should not be driven until repaired as the airbag system is compromised and may not deploy properly in a collision, significantly increasing injury risk. The airbag warning light will remain illuminated, and some or all airbags may be deactivated.
Common Causes
45%
Damaged wiring harness or corroded connector at crash sensor #2 due to environmental exposure or previous collision damage
30%
Failed or internally damaged crash sensor #2
15%
Poor ground connection or broken ground wire in sensor circuit
10%
Airbag control module internal circuit fault or damaged connector pins
Diagnostic Steps
1
Step 1: Perform visual inspection of crash sensor #2 (typically located in front bumper, side pillar, or underbody depending on vehicle) and its wiring harness for physical damage, corrosion, loose connectors, or previous collision damage
2
Step 2: Using a digital multimeter, backprobe the crash sensor #2 connector and verify supply voltage (typically 5-12V depending on manufacturer) and ground continuity with ignition on. Check for voltage drop exceeding 0.2V on ground circuit
3
Step 3: Disconnect crash sensor #2 and measure resistance across sensor terminals per manufacturer specifications (typically 1-5 kΩ). Compare readings to known-good values to determine if sensor is within tolerance
4
Step 4: Check continuity and resistance of wiring harness between crash sensor #2 and airbag control module with all connectors disconnected. Look for opens, shorts to ground, or shorts to power (resistance should be less than 5Ω for continuity)
5
Step 5: Inspect airbag control module connector for bent pins, corrosion, or moisture intrusion. Clean or repair connector as needed
6
Step 6: Clear codes, perform test drive, and verify repair by monitoring live data for crash sensor #2 feed voltage and system status
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
This code indicates the Airbag Control Module (ACM) has detected an electrical fault in the power supply (feed) or ground (return) circuit for crash sensor #2. The sensor is not receiving proper voltage or cannot complete its circuit path, preventing the ACM from monitoring impact data from this spe...
The most common cause of B1904 (Air Bag Crash Sensor #2 Feed/Return Circuit Failure) is: Damaged wiring harness or corroded connector at crash sensor #2 due to environmental exposure or previous collision damage
Typical repair costs for B1904 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle should not be driven until repaired as the airbag system is compromised and may not deploy properly in a collision, significantly increasing injury risk. The airbag warning light will remain illuminated, and some or all airbags may be deactivated.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to B1904 to identify the root cause.
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Quick Info
Category
Body
System
Supplemental Restraint System (SRS/Airbag)
Difficulty
Type
Manufacturer
Recommended Tools
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