Introduction
The B1812 Diagnostic Trouble Code (DTC) indicates a "Lamp Backup Switch Input Circuit Short To Battery." This means the vehicle's computer (often the Powertrain Control Module or PCM) has detected an unexpected voltage on the circuit that connects the backup lamp switch (also known as the reverse light switch) to the vehicle's electrical system. This "short to battery" condition suggests that the wiring or components within the circuit are allowing voltage from the vehicle's battery to reach the backup lamp switch input in a way that isn't intended. This can cause the reverse lights to illuminate even when the vehicle is not in reverse, drain the battery, or prevent the reverse lights from working at all when they are supposed to. Diagnosing and repairing this issue promptly is essential to ensure proper vehicle operation and prevent further electrical damage.
B1812 Code Information
| Topic | Description | Possible Causes |
|---|---|---|
| Definition | Lamp Backup Switch Input Circuit Short To Battery. The PCM detects voltage where it shouldn't be, indicating a short circuit to the positive (battery) side of the electrical system. | - Shorted wiring harness or connector near the backup lamp switch. - Shorted backup lamp switch itself. - Damaged wiring harness rubbing against the vehicle frame or engine components. - Faulty PCM (rare). - Water intrusion into the circuit. |
| Symptoms | - Reverse lights illuminated constantly, even when the vehicle is not in reverse. - Battery drain. - Reverse lights not functioning when the vehicle is in reverse. - Other seemingly unrelated electrical problems. |
- Wiring issues causing unintended power flow. - Failed switch permanently closing the circuit. - Corroded connections. - Incorrectly installed aftermarket accessories interfering with the circuit. |
| Diagnostic Steps | - Visual inspection of wiring and connectors. - Testing the backup lamp switch for proper function. - Checking for voltage on the backup lamp switch input circuit with a multimeter. - Inspecting for chafed or damaged wiring. - Testing circuit continuity. |
- Methodical approach to isolate the short. - Use of wiring diagrams is crucial. - Component isolation to pinpoint the faulty part. - Proper use of diagnostic tools. |
| Related Codes | - B1811 (Lamp Backup Switch Input Circuit Open). - Other body control module (BCM) or PCM codes related to lighting or electrical systems. |
- Understanding related codes can provide context. - Consider other potential faults in the electrical system. |
| Severity | Moderate to High. | - Constant illumination of reverse lights can attract unwanted attention and potentially drain the battery. - Failure of reverse lights can be a safety hazard. |
| Common Repair Solutions | - Repairing or replacing damaged wiring. - Replacing the backup lamp switch. - Repairing or replacing corroded connectors. - PCM replacement (rare, only if confirmed faulty). |
- Addressing the root cause of the short is essential. - Thorough inspection after repair to ensure the issue is resolved. |
| Tools Required | - Multimeter. - Wiring diagrams. - Wire strippers/crimpers. - Socket set. - Test light. |
- Having the right tools saves time and frustration. - Wiring diagrams are crucial for accurate diagnosis. |
| Potential for DIY Repair | Moderate. | - Requires basic electrical knowledge and the ability to use a multimeter. - Wiring repairs should be done carefully and correctly. - If unsure, consult a qualified mechanic. |
Detailed Explanations
Definition: The B1812 code signifies that the vehicle's computer has detected an unintended voltage source on the circuit dedicated to the backup lamp switch. This circuit is designed to only receive voltage when the transmission is in reverse, activating the reverse lights. The code indicates that voltage, typically battery voltage (12V), is present on this circuit even when the vehicle is not in reverse. This "short to battery" situation implies a direct connection to the positive side of the vehicle's electrical system, bypassing the intended control mechanism.
Symptoms: The most obvious symptom is that the reverse lights stay on constantly, regardless of the gear selected. This constant illumination can lead to a significant battery drain, especially if the vehicle is left parked for extended periods. Conversely, in some cases, the reverse lights might not work at all when the vehicle is placed in reverse. This can happen if the short to battery is interfering with the normal operation of the switch. Less obvious symptoms might include other seemingly unrelated electrical problems, depending on the severity and location of the short.
Diagnostic Steps: The diagnostic process begins with a visual inspection of the wiring harness and connectors associated with the backup lamp switch, looking for signs of damage, corrosion, or chafing. Next, the backup lamp switch itself should be tested to ensure it's functioning correctly. A multimeter is used to check for voltage on the backup lamp switch input circuit while the vehicle is not in reverse. If voltage is present, the technician needs to inspect the wiring harness more thoroughly, looking for areas where the insulation may be damaged and the wire is shorting to a positive voltage source. Finally, circuit continuity can be tested to confirm the presence of a short circuit.
Related Codes: While B1812 specifically points to a short to battery in the backup lamp switch circuit, other codes can provide valuable context. For example, a B1811 (Lamp Backup Switch Input Circuit Open) indicates an open circuit, which is the opposite problem but could be related to damaged wiring in the same harness. Codes related to the Body Control Module (BCM) or PCM might also be present, suggesting a broader electrical issue. Understanding these related codes can help narrow down the root cause of the problem.
Severity: The severity of a B1812 code can range from moderate to high. The constant illumination of the reverse lights is a nuisance and can attract unwanted attention from other drivers and law enforcement. More importantly, it can lead to a significant battery drain, potentially leaving you stranded. The failure of the reverse lights to operate when needed is a safety hazard, as it reduces visibility when backing up and can increase the risk of an accident.
Common Repair Solutions: The most common solution involves repairing or replacing damaged wiring that is causing the short to battery. This might involve splicing in new sections of wire or replacing the entire harness. Another common fix is replacing the backup lamp switch itself, especially if it's found to be internally shorted. Corroded connectors can also cause electrical problems and should be cleaned or replaced. In rare cases, the PCM may be faulty and require replacement, but this should only be considered after all other possibilities have been ruled out.
Tools Required: To properly diagnose and repair a B1812 code, several tools are essential. A multimeter is used to measure voltage, resistance, and continuity. Wiring diagrams are crucial for understanding the circuit layout and identifying the correct wires to test. Wire strippers and crimpers are needed for repairing damaged wiring. A socket set is required to remove and install the backup lamp switch. A test light can be helpful for quickly checking for voltage.
Potential for DIY Repair: Repairing a B1812 code is considered a moderate DIY project. It requires a basic understanding of automotive electrical systems and the ability to use a multimeter safely and effectively. Wiring repairs should be done carefully and correctly to avoid further problems. If you are unsure about any aspect of the repair, it's best to consult a qualified mechanic.
Frequently Asked Questions
What does the B1812 code mean? It indicates a short to battery in the backup lamp switch input circuit, meaning the circuit is receiving voltage when it shouldn't be.
What are the symptoms of a B1812 code? The most common symptom is reverse lights staying on constantly, even when the vehicle isn't in reverse.
Can a bad backup lamp switch cause the B1812 code? Yes, an internally shorted backup lamp switch can cause this code.
How do I diagnose a B1812 code? Use a multimeter to check for voltage on the backup lamp switch input circuit when the vehicle is not in reverse, and inspect the wiring for damage.
Is it safe to drive with a B1812 code? While you can drive, it's not recommended due to the potential for battery drain and the risk of not having functioning reverse lights.
How do I fix a B1812 code? Repair or replace damaged wiring, replace the backup lamp switch, or repair corroded connectors.
Conclusion
The B1812 code signifies a "Lamp Backup Switch Input Circuit Short To Battery," indicating an unintended voltage on the reverse light circuit. Prompt and accurate diagnosis and repair are crucial to prevent battery drain, ensure proper reverse light function, and maintain vehicle safety. Addressing the root cause of the short circuit, whether it's damaged wiring or a faulty switch, is essential for a lasting solution.