The diagnostic trouble code (DTC) B2947 indicates a "Security System Sensor Power Circuit Low" condition. This means the vehicle's computer, often the body control module (BCM) or a dedicated security module, has detected that the voltage in the power circuit supplying the security system sensors is lower than expected. This can disable or impair the functionality of the vehicle's security system, leaving it vulnerable to theft or unauthorized access. Addressing this code promptly is crucial for maintaining the security of your vehicle.
| Category | Description | Possible Causes |
|---|---|---|
| Symptom | Security system malfunction or inoperative. | Security system fails to arm or disarm. Alarm system triggers intermittently or not at all. Power door locks may malfunction. Remote keyless entry (RKE) may be unresponsive. Vehicle may not start (in some systems). |
| Affected Components | Security system sensors (door sensors, hood sensor, trunk sensor, glass breakage sensor, motion sensor, etc.), wiring harness, connectors, BCM, security module, power supply circuits. | Damaged or corroded wiring or connectors. Short to ground in the sensor power circuit. Faulty security system sensor. Low battery voltage. Failing BCM or security module. Blown fuse or open circuit in the power supply. |
| Diagnostic Steps | Visual inspection of wiring and connectors. Voltage testing of the sensor power circuit. Sensor testing. Fuse and relay checks. BCM/Security module diagnostics. | Check for chafed or damaged wiring around the sensors. Inspect connectors for corrosion or loose connections. Use a multimeter to measure voltage at the sensor power supply wire. Test individual sensors for proper operation. Check fuses and relays related to the security system. |
| Potential Solutions | Repair or replace damaged wiring or connectors. Replace faulty security system sensor. Replace blown fuse or faulty relay. Recharge or replace low battery. Replace faulty BCM or security module. | Repair any short circuits to ground. Clean corroded connections. Ensure proper grounding of the security system. Reprogram the BCM or security module (if applicable). Test the system after repairs to ensure proper functionality. |
| Related Codes | B2945 (Security System Sensor Power Circuit High), B1000 (ECU Malfunction), other security system related DTCs. | These codes may indicate related problems within the security system or the BCM. Addressing these codes may be necessary to resolve the B2947 code. |
| Sensor Types | Door ajar sensors, hood switch, trunk/hatch switch, glass breakage sensors, interior motion sensors, tilt sensors. | Each sensor provides a signal to the security module indicating the status of its monitored area. Failure of any of these sensors can trigger the B2947 code if they are drawing excessive current or shorting to ground. |
| Power Circuit Details | Typically a 5V or 12V circuit powered by the BCM or security module. | The voltage and current capacity of the circuit are critical for proper sensor operation. A drop in voltage can indicate a problem in the wiring, a failing power supply, or excessive current draw from a failing sensor. |
| Grounding Issues | Poor grounding can lead to voltage drops and intermittent sensor operation. | Ensure all ground connections for the security system and sensors are clean, tight, and free of corrosion. Add additional grounding points if necessary to improve system performance. |
| Scan Tool Data | Some scan tools can display live data from the security system, including sensor status and voltage readings. | This data can be invaluable for pinpointing the specific sensor or circuit causing the problem. Look for erratic or out-of-range readings from the sensors. |
Detailed Explanations
Symptom: The most obvious symptom is a malfunctioning or inoperative security system. This can manifest in several ways, including the system failing to arm or disarm when commanded, the alarm triggering randomly or not at all, power door locks malfunctioning, remote keyless entry failing to respond, or, in some cases, the vehicle refusing to start due to the security system's immobilizer function. The specific symptoms depend on the design and features of the vehicle's security system.
Affected Components: The B2947 code can be triggered by problems in various components. This includes the security system sensors themselves (such as door sensors, hood sensors, trunk sensors, glass breakage sensors, or motion sensors), the wiring harness and connectors that connect these sensors to the control module, the BCM or dedicated security module that controls the system, and the power supply circuits that provide power to the sensors. A problem in any of these areas can cause a low voltage condition in the sensor power circuit.
Diagnostic Steps: Diagnosing a B2947 code requires a systematic approach. Start with a visual inspection of the wiring and connectors associated with the security system sensors, looking for any signs of damage, corrosion, or loose connections. Next, use a multimeter to test the voltage of the sensor power circuit at various points, comparing the readings to the expected voltage (typically 5V or 12V). You can also test individual sensors to ensure they are operating correctly and not drawing excessive current. Check the fuses and relays that are related to the security system, as a blown fuse or faulty relay can cause a voltage drop. Finally, use a scan tool to perform BCM/Security module diagnostics, looking for any stored codes or data that might provide further clues.
Potential Solutions: The solution to a B2947 code depends on the underlying cause. If you find damaged wiring or connectors, repair or replace them. If a security system sensor is faulty, replace it. If a fuse is blown or a relay is faulty, replace it. If the battery voltage is low, recharge or replace the battery. In rare cases, the BCM or security module itself may be faulty, requiring replacement.
Related Codes: The B2947 code may be accompanied by other related codes, such as B2945 (Security System Sensor Power Circuit High), B1000 (ECU Malfunction), or other security system-specific DTCs. These codes can provide additional information about the nature of the problem and may need to be addressed in order to resolve the B2947 code. For example, a B1000 code could indicate an internal problem with the BCM, which could be causing the low voltage condition.
Sensor Types: Various types of sensors are used in vehicle security systems to detect intrusion. Door ajar sensors monitor the opening and closing of doors. A hood switch detects if the hood is opened. A trunk/hatch switch performs a similar function for the trunk or hatch. Glass breakage sensors detect the sound of breaking glass. Interior motion sensors detect movement inside the vehicle. Tilt sensors detect if the vehicle is being tilted, such as during a towing attempt. Each sensor provides a signal to the security module, and a problem with any of these sensors can trigger the B2947 code.
Power Circuit Details: The security system sensors are typically powered by a 5V or 12V circuit supplied by the BCM or security module. The voltage and current capacity of this circuit are critical for proper sensor operation. A drop in voltage can indicate a problem in the wiring, a failing power supply, or excessive current draw from a failing sensor. Understanding the specific voltage requirements of the sensor circuit for your vehicle is crucial for accurate diagnosis. Refer to the vehicle's service manual for this information.
Grounding Issues: Poor grounding can be a significant contributor to voltage drops and intermittent sensor operation. Ensure that all ground connections for the security system and sensors are clean, tight, and free of corrosion. Consider adding additional grounding points to improve system performance, especially if you suspect a grounding problem. A poor ground can cause the sensors to not function correctly, leading to false alarms or a complete system failure.
Scan Tool Data: A scan tool can be a valuable tool for diagnosing B2947. Some scan tools are capable of displaying live data from the security system, including sensor status and voltage readings. This data can help you pinpoint the specific sensor or circuit that is causing the problem. Look for erratic or out-of-range readings from the sensors, which can indicate a faulty sensor or a wiring problem. Analyzing the live data can significantly reduce diagnostic time.
Frequently Asked Questions
What does the B2947 code mean? The B2947 code indicates a low voltage condition in the power circuit supplying the security system sensors. This can prevent the security system from functioning correctly.
Can I fix the B2947 code myself? Depending on your mechanical skills and access to tools, you may be able to diagnose and repair some causes of the B2947 code, such as replacing a blown fuse or repairing damaged wiring. However, more complex issues may require professional diagnosis and repair.
What are the common causes of the B2947 code? Common causes include damaged wiring, faulty sensors, blown fuses, a low battery, or a failing BCM or security module. Corrosion on connectors can also play a role.
How do I test the security system sensors? Use a multimeter to check the voltage and continuity of the sensor circuits. Refer to the vehicle's service manual for specific testing procedures for each sensor.
Will the B2947 code affect my car's starting ability? In some vehicles, the security system is integrated with the engine immobilizer, and a B2947 code can prevent the car from starting.
Conclusion
The B2947 code signifies a low voltage condition in the security system sensor power circuit, which can compromise your vehicle's security. By systematically diagnosing the potential causes and following the appropriate repair procedures, you can restore the functionality of your security system and protect your vehicle from theft. Consult a qualified automotive technician if you are unsure about any aspect of the diagnosis or repair process.