B1904: Impact Sensor #2 Circuit Malfunction
Diagnostic trouble code B1904 indicates that the Restraint Control Module (RCM) has detected a fault in the feed/return circuit of Impact Sensor #2. This sensor, typically located on the side or front of the vehicle, provides deceleration data to the RCM. The fault may be due to an open circuit, short to ground, short to battery voltage, or out-of-range resistance in the wiring or sensor itself, preventing proper communication.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty impact sensor #2 (side or front)
- Open, shorted to ground, or shorted to voltage in the sensor #2 feed/return circuit wiring
- Damaged, corroded, or loose terminals in the sensor #2 connector
- Internal failure of the Restraint Control Module (RCM)
- Physical damage to the wiring harness from a previous collision or rodent activity
3. Symptoms You Will Notice
- Airbag warning light illuminated on the dashboard
- Possible deactivation of the supplemental restraint system (SRS)
4. Step-by-Step Diagnosis
Scan the RCM for B1904 and any related codes.
Visually inspect the impact sensor #2 connector and wiring for damage, corrosion, or loose connections.
Test the sensor #2 feed/return circuit for continuity, shorts to ground, and shorts to battery voltage using a multimeter.
If wiring is intact, substitute a known-good impact sensor #2 and retest.
If the code persists, suspect an internal RCM fault and perform further diagnostics per manufacturer procedures.
5. Frequently Asked Questions
Is it safe to drive?▼
No, it is not safe to drive. This code indicates a critical fault in the airbag system, which may prevent deployment in a collision, increasing the risk of injury.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on whether the sensor, wiring, or RCM needs replacement, and labor rates.