The B1979 diagnostic trouble code (DTC) indicates a fault within the passenger seat's rearward switch circuit, specifically a short to the battery voltage. This means the circuit is unintentionally receiving power directly from the vehicle's battery, potentially causing the seat motor to operate unexpectedly, drain the battery, or even pose a fire hazard. Understanding the causes, symptoms, and troubleshooting steps for a B1979 code is crucial for ensuring the safety and functionality of your vehicle.
This article provides a comprehensive guide to understanding, diagnosing, and potentially resolving the B1979 trouble code related to the passenger seat rearward switch circuit. We will cover potential causes, common symptoms, diagnostic procedures, and frequently asked questions to equip you with the knowledge necessary to address this issue effectively.
| Topic | Description | Potential Causes |
|---|---|---|
| B1979 Code Definition | Indicates a short to battery voltage in the passenger seat rearward switch circuit. This means the circuit is receiving unintended power directly from the battery. | Damaged Wiring: Frayed, cracked, or exposed wires in the seat wiring harness. Faulty Switch: A malfunctioning rearward switch that is internally shorted. Short to Power: The circuit wire comes into contact with a wire providing direct battery voltage. Damaged Connector: Corroded or loose connector pins on the seat switch or the seat control module. |
| Common Symptoms | The passenger seat moves rearward without input from the switch, the seat motor operates continuously, the battery drains quickly, the seat switch is unresponsive, or related seat functions (lumbar support, seat heater) malfunction. | Seat Movement Without Input: A constant signal from the switch due to the short. Battery Drain: The continuous operation of the seat motor or power draw through the short. Unresponsive Switch: The short overrides the normal switch function. Related Function Issues: The short interferes with the operation of other seat features. |
| Diagnostic Procedures | Visual inspection of wiring and connectors, multimeter testing for shorts to voltage, circuit continuity testing, switch testing, and module testing. | Visual Inspection: Look for obvious damage to wiring, connectors, and the seat switch. Multimeter Testing: Identify the short to voltage by checking for voltage on the circuit when it should be off. Continuity Testing: Confirm the presence of a short to ground or other wires. Switch Testing: Verify the switch is functioning correctly and not internally shorted. Module Testing: Rule out the seat control module as the source of the problem. |
| Potential Solutions | Repair or replace damaged wiring, replace the faulty rearward switch, repair or replace damaged connectors, replace the seat control module (in rare cases), and clear the DTC after repairs. | Wiring Repair/Replacement: Fixing any breaks, frays, or shorts in the wiring harness. Switch Replacement: Installing a new, properly functioning rearward switch. Connector Repair/Replacement: Cleaning or replacing corroded or damaged connectors. Module Replacement: Replacing the seat control module if it is determined to be the root cause (least likely). |
| Safety Precautions | Disconnect the battery before working on electrical components, use appropriate safety gear (gloves, eye protection), and be careful when working around moving seat mechanisms. | Battery Disconnection: Prevents accidental shorts and electrical shocks. Safety Gear: Protects against electrical hazards and moving parts. Seat Mechanism Awareness: Avoid getting hands or fingers caught in the seat mechanism. |
| Required Tools | Multimeter, wiring diagram, wire stripper, crimper, electrical tape, connector cleaning tools, and possibly a seat control module scanner. | Multimeter: For voltage, continuity, and resistance testing. Wiring Diagram: To understand the circuit layout and identify the correct wires. Wire Stripper/Crimper: For repairing or replacing wiring. Electrical Tape: For insulating repaired wires. Connector Cleaning Tools: To remove corrosion from connectors. Scanner: To read and clear DTCs. |
Detailed Explanations
B1979 Code Definition:
The B1979 code, as reported by your vehicle's onboard diagnostic system, specifically points to an electrical fault within the passenger seat's rearward switch circuit. More precisely, it indicates a short to battery voltage. This means that the circuit, which should only receive power when the rearward seat switch is activated, is instead receiving a constant supply of power directly from the vehicle's battery. This unintended power flow can lead to various problems, as outlined in the symptoms section.
Common Symptoms:
The symptoms associated with a B1979 code can range from minor inconveniences to potentially serious issues. One of the most noticeable symptoms is the passenger seat moving rearward without any input from the switch. This occurs because the short to battery voltage is effectively mimicking the switch being constantly pressed. Another common symptom is a rapid battery drain, as the seat motor may be operating continuously or drawing power even when the vehicle is off. You might also find that the seat switch is unresponsive or that other related seat functions, such as lumbar support or seat heating, are malfunctioning due to the electrical interference caused by the short.
Diagnostic Procedures:
A systematic diagnostic approach is essential for accurately pinpointing the source of the B1979 code. The first step is a thorough visual inspection of the wiring harness under the seat, looking for any signs of damage, such as frayed wires, cracked insulation, or corroded connectors. Next, a multimeter is used to test the circuit for shorts to voltage. This involves checking for voltage on the circuit wires when the switch is in the "off" position. Continuity testing can also reveal shorts to ground or other wires within the harness. The seat switch itself should be tested to ensure it is functioning correctly and not internally shorted. Finally, although less common, the seat control module should be considered as a potential cause, especially if other diagnostic steps fail to identify the problem.
Potential Solutions:
Once the cause of the B1979 code has been identified, the appropriate solution can be implemented. Repairing or replacing damaged wiring is often necessary, especially if frayed wires or cracked insulation are found. A faulty rearward switch should be replaced with a new, properly functioning switch. Damaged connectors should be either repaired or replaced to ensure a solid electrical connection. In rare cases, if the seat control module is determined to be the source of the problem, it may need to be replaced. After any repairs are completed, it's important to clear the DTC using a scan tool to ensure the problem has been resolved and the warning light is turned off.
Safety Precautions:
Working on automotive electrical systems requires adherence to strict safety precautions. Always disconnect the battery before starting any work to prevent accidental shorts and electrical shocks. Wear appropriate safety gear, such as gloves and eye protection, to protect yourself from potential hazards. Be particularly careful when working around moving seat mechanisms to avoid getting your hands or fingers caught. Understanding the electrical system layout using a wiring diagram is also crucial to avoid damaging other components.
Required Tools:
Having the right tools on hand is essential for efficient and accurate diagnosis and repair. A multimeter is indispensable for measuring voltage, continuity, and resistance. A wiring diagram will help you understand the circuit layout and identify the correct wires. Wire strippers and crimpers are necessary for repairing or replacing wiring. Electrical tape is used to insulate repaired wires. Connector cleaning tools can help remove corrosion from connectors. Finally, a scan tool may be needed to read and clear DTCs.
Frequently Asked Questions
What does a B1979 code mean? It means there's a short to battery voltage in the passenger seat rearward switch circuit, causing unintended power flow.
What are the most common symptoms of a B1979 code? The passenger seat may move rearward without input, the battery might drain quickly, or the seat switch may be unresponsive.
Can I fix a B1979 code myself? Yes, if you have experience with automotive electrical systems and the necessary tools. However, improper repairs can be dangerous.
What if the seat switch is not the problem? Check the wiring harness for damage, test the connectors, and consider the seat control module as a possible cause.
Is it safe to drive with a B1979 code? It's not recommended, as the seat may move unexpectedly, potentially causing a distraction or safety hazard. Additionally, the battery drain could leave you stranded.
Conclusion
The B1979 code, indicating a short to battery in the passenger seat rearward switch circuit, requires careful diagnosis and repair. By understanding the potential causes, symptoms, and diagnostic procedures outlined in this guide, you can effectively address this issue and ensure the safety and functionality of your vehicle.