B1808 Lamp Tail Output Circuit Short To Battery

The B1808 Diagnostic Trouble Code (DTC) indicates a "Lamp Tail Output Circuit Short To Battery" in a vehicle's electrical system. This means the circuit responsible for powering the tail lights has an unintended connection to the vehicle's battery voltage. This short circuit can cause the tail lights to remain constantly illuminated, drain the battery, and potentially damage electrical components. Troubleshooting and resolving this issue is crucial for safety, preventing further damage, and ensuring proper vehicle operation.

Comprehensive Table: B1808 - Lamp Tail Output Circuit Short To Battery

Detailed Explanations

Definition: Lamp Tail Output Circuit Short To Battery: This refers to an unintended electrical connection occurring in the tail light circuit that results in the circuit being directly connected to the vehicle's battery voltage. This bypasses the normal switching and control mechanisms, causing the tail lights to remain constantly on.

Symptoms:

• Tail lights constantly illuminated: This is the most obvious symptom. The tail lights remain on even when the vehicle is turned off, and the light switch is in the "off" position.
• Battery drain: The constant draw of power from the tail lights will quickly drain the vehicle's battery, especially if the vehicle is left parked for an extended period.
• Blown fuses: The excessive current flowing through the circuit due to the short can cause the tail light fuse to blow repeatedly. Replacing the fuse without addressing the underlying short will only result in the fuse blowing again.
• Malfunctioning lighting control module: The short circuit can potentially damage the lighting control module (BCM) due to the excessive current flow. This can lead to other lighting-related problems.
• Dim headlights: In some scenarios, the short circuit can affect other lighting circuits, causing the headlights to dim or flicker.

Possible Causes:

• Damaged wiring: This is a very common cause. Worn, frayed, cracked, or rodent-damaged wiring insulation can expose the conductor, allowing it to come into contact with a power source (in this case, battery voltage).
• Corroded connectors: Corrosion in connectors can create conductive paths, allowing voltage to leak into the tail light circuit.
• Faulty tail light assembly: Internal shorts within the tail light assembly itself can cause the tail lights to stay on. This could be due to damage to the circuit board or wiring within the assembly.
• Wiring harness damage: The wiring harness that carries the tail light circuit can be damaged due to physical impact, rubbing against sharp edges, or rodent activity.
• Shorted bulb socket: A short circuit can occur within the bulb socket itself, often due to corrosion or physical damage.
• Faulty lighting control module (BCM): Although less common, the lighting control module (BCM) can internally fail and cause a short circuit in the tail light output circuit.

Diagnostic Steps:

• Visual inspection: Carefully inspect all wiring, connectors, and tail light assemblies for any signs of damage, corrosion, or loose connections. Pay close attention to areas where the wiring harness might be exposed to rubbing or physical damage.
• Fuse check: Check the tail light fuse for blown condition. If the fuse is blown, replace it with a fuse of the correct amperage rating. If the fuse blows again immediately or soon after replacement, it confirms a short circuit.
• Multimeter testing (Voltage & Continuity): Use a multimeter to check for voltage on the tail light circuit when the tail lights should be off (e.g., ignition off, light switch off). If voltage is present, it indicates a short to battery. Then, perform continuity testing to isolate the location of the short. Disconnect components one by one and check for continuity between the tail light circuit and ground.
• Wiring diagram analysis: Consult the vehicle's wiring diagram to understand the tail light circuit layout and identify potential short locations. The wiring diagram will show the path of the circuit, the location of connectors, and the components involved.
• Component isolation: Disconnect components (tail light assemblies, lighting control module) one by one to isolate the source of the short. For example, disconnect the tail light assemblies. If the fuse no longer blows, the short is likely within one of the tail light assemblies.
• Scan tool diagnostics: Use a scan tool to read diagnostic trouble codes and live data from the lighting control module. This can provide valuable information about the circuit's performance and identify any other related issues.

Repair Procedures:

• Wiring repair: Repair or replace damaged wiring, ensuring proper insulation and connections. Use appropriate wire strippers, crimpers, and electrical tape or heat shrink tubing to make secure and reliable connections.
• Connector cleaning/replacement: Clean corroded connectors with electrical contact cleaner or replace them with new ones. Ensure the connectors are properly seated and locked.
• Tail light assembly replacement: Replace faulty tail light assemblies with new or refurbished units. Ensure the replacement assembly is compatible with the vehicle's electrical system.
• Wiring harness repair/replacement: Repair damaged sections of the wiring harness or replace the entire harness if necessary. This can be a more complex repair, but it may be required if the damage is extensive.
• Bulb socket replacement: Replace the shorted bulb socket with a new one. Ensure the replacement socket is compatible with the bulb type.
• Lighting control module replacement/reprogramming: Replace the faulty lighting control module and reprogram it if necessary. Reprogramming may be required to ensure the new module functions correctly with the vehicle's other systems.

Tools Required:

• Multimeter: Essential for testing voltage, continuity, and resistance to diagnose electrical problems.
• Wiring diagram: Crucial for understanding the circuit layout and identifying potential short locations.
• Wire strippers/crimpers: For repairing or replacing wiring.
• Electrical tape/heat shrink tubing: For insulating wiring connections.
• Socket set/wrenches: For removing and installing components.
• Scan tool: For reading diagnostic trouble codes and live data.
• Test light: A simpler tool for quickly checking if a circuit is powered.

Safety Precautions:

• Disconnect the battery: Always disconnect the negative battery terminal before working on the electrical system to prevent accidental shocks or further damage.
• Wear safety glasses: Protect your eyes from debris when working on electrical components.
• Use insulated tools: Use insulated tools to prevent electrical shocks.
• Avoid working in wet conditions: Avoid working on the electrical system in wet conditions to prevent electrical shocks.

Related DTCs:

• B1801 - Lamp Tail Output Circuit Open: This code indicates an open circuit in the tail light circuit, meaning there is a break in the circuit.
• B1802 - Lamp Tail Output Circuit Short To Ground: This code indicates a short circuit to ground in the tail light circuit, meaning the circuit is unintentionally connected to the vehicle's chassis.
• Other lighting related DTCs: DTCs related to other lighting circuits such as headlights, brake lights, or turn signals. The presence of other lighting-related codes can help narrow down the potential cause of the B1808 code.

Severity: The B1808 code indicates a serious electrical fault that can lead to battery drain, safety hazards (constantly illuminated tail lights), and potential damage to electrical components. Immediate diagnosis and repair are recommended.

Common Vehicle Makes/Models: This code is not specific to any one make or model. It can occur in a wide range of vehicles with electronic lighting control systems.

Location of Tail Light Wiring Harness: The tail light wiring harness typically runs along the frame rails or inside the vehicle, often under the carpeting or headliner, to the rear of the vehicle. Consult your vehicle's service manual for exact routing.

Cost of Repair: The cost of repair can vary depending on the cause of the short circuit and the labor required. Wiring repairs and connector replacements are generally less expensive than replacing the lighting control module or wiring harness.

Time to Diagnose: Diagnosis can take anywhere from 30 minutes to several hours, depending on the complexity of the issue and the technician's experience.

Preventative Measures:

• Regular inspection: Periodically inspect wiring and connectors for signs of damage or corrosion.
• Proper maintenance: Follow the vehicle manufacturer's recommended maintenance schedule.
• Avoid overloading circuits: Avoid adding excessive electrical accessories that could overload the tail light circuit.

Frequently Asked Questions

What does the B1808 code mean? It means there's an unintended electrical connection causing the tail light circuit to be directly connected to the battery voltage.

Can I drive with the B1808 code? Driving is not recommended because the constantly illuminated tail lights can confuse other drivers and the battery will drain.

How do I fix the B1808 code? Diagnose the cause of the short circuit using a multimeter and wiring diagrams, then repair or replace the damaged wiring or components.

Will replacing the tail light bulbs fix the B1808 code? No, replacing the bulbs will not fix the problem if there is a short to battery in the circuit.

Is the B1808 code a serious problem? Yes, it's a serious electrical fault that can lead to battery drain, safety hazards, and potential damage to electrical components.

Conclusion

The B1808 code "Lamp Tail Output Circuit Short To Battery" signifies a critical electrical fault that requires prompt attention. By systematically diagnosing the issue using the steps outlined above and addressing the root cause of the short circuit, you can restore the tail light circuit to proper operation and prevent further damage to your vehicle.