B3904 Buick 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 Buick 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 Buick 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 Buick?
- 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 Buick?
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 Buick 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.
Need more information about the B3904 Buick code?
Need more information on how to fix the B3904 Buick code? Get Access to Factory Service Manuals
Need Help with the Code?
Get the B3904 Buick code diagnosed by a professional: Find a repair shop in your area
Frequently Asked Questions about B3904 Buick Code
1. What does the OBDII code B3904 mean for a Buick?
The code B3904 indicates that the rear compartment occupant sensor signal is invalid, often tied to a fault in detecting passenger presence or weight in the rear seat.
2. What are the common symptoms of code B3904 in a Buick?
Symptoms may include malfunctioning rear seat occupant detection system, airbag warning light illumination, or incorrect airbag deployment behavior.
3. What causes the B3904 code to appear in a Buick?
Common causes include a faulty rear occupant sensor, damaged wiring or connectors, or a problem with the control module responsible for the sensor.
4. Can driving with the B3904 code cause safety issues?
Yes, it may affect airbag deployment logic, potentially compromising passenger safety in the event of a collision.
5. How is the B3904 code diagnosed in a Buick?
Technicians use an OBDII scanner to verify the code, inspect the rear occupant sensor, and check for wiring or connector damage.
6. How can I fix the B3904 code in a Buick?
Repairs may involve replacing the rear occupant sensor, repairing damaged wiring or connectors, or reprogramming the control module.
7. Is replacing the rear occupant sensor expensive?
Costs vary depending on the model and labor rates, but replacement typically ranges from $150 to $400.
8. Can the B3904 code be cleared without repairs?
Clearing the code without addressing the root cause may only provide a temporary fix, as the issue will likely return.
9. Can I reset the B3904 code myself?
You can clear the code using an OBDII scanner, but if the underlying problem isn’t fixed, it will reappear.
10. What should I do if the B3904 code persists after repairs?
If the code persists, recheck the wiring, sensor installation, and control module programming, or consult a qualified technician for further diagnosis.
Discuss the causes and fixes for B3904 Buick OBDII Code
Code B3904 Buick comments
No comments found for this page.
Fix Your Car Smarter
Try the New AutoCodes App!
Get complete OBDII diagnostics, repair solutions, and cost estimates, plus AI chat support on demand.
