B3891 Code - Trailer Fog Lamps Circuit
Quick Answer
The Trailer Lighting Control Module receives a serial data message from the Body Control Module (BCM) indicating that the vehicle rear fog lamp have been activated. Common causes include Faulty Trailer Fog Lamps, Trailer Fog Lamps harness is open or shorted, Trailer Fog Lamps 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
- B3891 indicates Trailer Fog Lamps Circuit.
- Common causes
- Common causes include Faulty Trailer Fog Lamps, Trailer Fog Lamps harness is open or shorted, Trailer Fog Lamps 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 B3891 Description
What are the Possible Causes of the DTC B3891?
- Faulty Trailer Fog Lamps
- Trailer Fog Lamps harness is open or shorted
- Trailer Fog Lamps circuit poor electrical connection
- Faulty Trailer Lighting Control Module
How to Fix the DTC B3891?
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.
Code Tech Notes
B3891 04 Trailer Fog Lamps Circuit Open
What is the Cost to Diagnose the Code?
Labor: 1.0
To diagnose the B3891 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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Information for Specific Makes
- B3891 Buick — Trailer Fog Lamps Circuit
- B3891 Cadillac — Trailer Fog Lamps Circuit
- B3891 Chevrolet — Trailer Fog Lamps Circuit
- B3891 GMC — Trailer Fog Lamps Circuit
Frequently Asked Questions about B3891 Code
1. What does OBDII code B3891 mean?
B3891 indicates a problem in the trailer fog lamps circuit, typically related to an open, short, or faulty connection.
2. What are the symptoms of code B3891?
Symptoms may include non-functional trailer fog lamps, a warning light on the dashboard, or a stored trouble code in the vehicle’s ECU.
3. What causes code B3891 to appear?
Common causes include damaged wiring, corroded connectors, a blown fuse, a faulty control module, or a malfunctioning trailer light bulb.
4. How can I diagnose code B3891?
Start by visually inspecting the trailer fog lamp wiring and connectors for damage or corrosion. Use a multimeter to check for continuity and proper voltage in the circuit.
5. Can I still drive with code B3891 active?
Yes, you can still drive, but the trailer fog lamps may not function, which could reduce visibility or safety when towing in foggy conditions.
6. How do I fix code B3891?
Repairs may involve replacing damaged wires, cleaning corroded connectors, replacing a blown fuse, or installing a new trailer fog lamp bulb.
7. Is code B3891 specific to certain vehicles?
This code is typically found in vehicles equipped with towing packages that include trailer fog lamps, but its presence depends on the manufacturer.
8. Can a faulty trailer module cause code B3891?
Yes, a malfunctioning trailer control module could disrupt the fog lamp circuit and trigger this code.
9. How much does it cost to repair code B3891?
Repair costs vary but may range from $50 to $200, depending on whether the issue involves simple wiring repairs or replacing components.
10. Can I clear code B3891 without fixing the issue?
You can clear the code with an OBDII scanner, but it will likely return if the underlying problem isn’t resolved.
Discuss the causes and fixes for B3891 OBDII Code
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