B3904 Cadillac Code - Rear Compartment Occupant Sensor Signal Invalid
Quick Answer
Rear compartment occupant sensor is connected to battery voltage and ground at all times. Common causes include Faulty Rear Compartment Occupant Sensor, Rear Compartment Occupant Sensor harness is open or shorted, Rear Compartment Occupant Sensor circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
- What it means
- B3904 Cadillac indicates Rear Compartment Occupant Sensor Signal Invalid.
- Common causes
- Common causes include Faulty Rear Compartment Occupant Sensor, Rear Compartment Occupant Sensor harness is open or shorted, Rear Compartment Occupant Sensor circuit poor electrical connection.
- Severity
- High - diagnose this code as soon as possible.
- Can I drive?
- Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
Code B3904 Cadillac Description
Rear compartment occupant sensor can be disabled by pressing disable switch on rear compartment occupant sensor and holding for 2 seconds. BCM will command trunk ajar telltale on for one minute with each ignition on signal while rear compartment occupant sensor is disabled. Once deck lid is opened, rear compartment occupant sensor will reset to on and resume normal operation. Rear compartment occupant sensor can also be enabled inside of rear compartment with ignition on or off by pressing disable switch. Deck lid ajar switch signal circuit is used for rear compartment occupant sensor class 2 data.
The Diagnostic Trouble Code (DTC) sets when BCM receives an invalid status signal from rear compartment occupant sensor.
What are the Possible Causes of the DTC B3904 Cadillac?
- Faulty Rear Compartment Occupant Sensor
- Rear Compartment Occupant Sensor harness is open or shorted
- Rear Compartment Occupant Sensor circuit poor electrical connection
- Faulty Body Control Module (BCM)
How to Fix the DTC B3904 Cadillac?
Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the B3904 Cadillac code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.
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Frequently Asked Questions about B3904 Cadillac Code
1. What does the OBDII code B3904 mean on a Cadillac?
B3904 indicates an issue with the rear compartment occupant sensor, where the sensor's signal is deemed invalid by the vehicle's control module.
2. What are the symptoms of code B3904 on a Cadillac?
Common symptoms include a non-functional rear occupant detection system, potential airbag system warnings, or the rear airbag being disabled.
3. What causes the B3904 code to appear?
The code may be triggered by a faulty rear occupant sensor, damaged wiring, loose connections, or a malfunctioning control module.
4. Can a blown fuse cause the B3904 code?
Yes, a blown fuse in the circuit related to the rear occupant sensor could cause the signal to be invalid and trigger the code.
5. How can I diagnose the B3904 code on a Cadillac?
Start by inspecting the rear occupant sensor, its wiring, and connectors for damage or loose connections. Use a scan tool to verify the sensor's data and confirm the fault.
6. Is it safe to drive with the B3904 code active?
While the vehicle may still be drivable, the airbag system may not function correctly for rear occupants, posing a safety risk in the event of a collision.
7. How do I fix the B3904 code on a Cadillac?
Repairs may include replacing the faulty rear occupant sensor, repairing damaged wiring, reseating loose connections, or addressing module issues if necessary.
8. Can a software update resolve the B3904 code?
In some cases, a software update for the vehicle's control module may fix the issue if it's caused by a programming error.
9. How much does it cost to repair the B3904 code?
Repair costs vary depending on the root cause but typically range from $100 to $300 for sensor replacement or wiring repairs.
10. Can I reset the B3904 code without repairs?
Clearing the code with an OBDII scanner may temporarily remove it, but the issue will likely recur unless the underlying problem is addressed.
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