Introduction:
The B1840 diagnostic trouble code (DTC) indicates a malfunction within the driver's seat lumbar support "up" switch circuit. This code signals that the vehicle's computer, specifically the Body Control Module (BCM) or Seat Control Module (SCM), has detected an issue with the electrical circuit responsible for activating the upward movement of the driver's seat lumbar support. Addressing this issue promptly ensures driver comfort and proper seat functionality, potentially preventing further electrical problems.
Comprehensive Overview of the B1840 Code
| Category | Description | Possible Causes |
|---|---|---|
| Code Definition | Driver Lumbar Up Switch Circuit Malfunction. Indicates the control module has detected an open or short circuit, or an out-of-range signal, in the wiring or components associated with the "up" function of the driver's lumbar support switch. | Faulty Driver Lumbar Up Switch: The switch itself is defective. Open or Short Circuit in Wiring: Damaged, corroded, or disconnected wires in the lumbar up switch circuit. Poor Electrical Connection: Loose or corroded connectors. Faulty Seat Control Module (SCM): The SCM is malfunctioning. Faulty Body Control Module (BCM): In some vehicles, the BCM controls the lumbar support function. |
| Symptoms | Lumbar support does not move upwards when the switch is activated. Intermittent lumbar support operation. The lumbar support may move in other directions (down, in, out) but not upwards. Check Engine Light (CEL) illumination (in some cases). | |
| Diagnostic Steps | Visual inspection of wiring and connectors. Testing the driver lumbar up switch for continuity and proper operation. Checking for voltage at the switch and the SCM. Inspecting the SCM for damage. Using a scan tool to monitor switch signal data. | |
| Possible Solutions | Replacing the faulty driver lumbar up switch. Repairing or replacing damaged wiring or connectors. Cleaning corroded connectors. Replacing the faulty Seat Control Module (SCM). Replacing the faulty Body Control Module (BCM) (rare). Clearing the B1840 code after repairs. | |
| Related Codes | B1835 (Driver Lumbar Down Switch Circuit Malfunction), B1845 (Driver Lumbar Forward/In Switch Circuit Malfunction), B1850 (Driver Lumbar Backward/Out Switch Circuit Malfunction). These codes indicate similar issues with other lumbar support functions. | |
| Severity | Low to Medium. While not critical to vehicle operation, a malfunctioning lumbar support can cause discomfort and fatigue, especially on long drives. Ignoring the issue could lead to further electrical problems. | |
| Common Vehicles Affected | Varies widely depending on vehicle make and model. Commonly seen in vehicles with power adjustable seats and lumbar support. Check specific manufacturer technical service bulletins (TSBs) for known issues. |
Detailed Explanations
Code Definition: The B1840 code specifically pinpoints a problem in the electrical circuit that controls the "up" function of the driver's seat lumbar support. The vehicle's computer, typically the Body Control Module (BCM) or the Seat Control Module (SCM), detects an irregularity in the signal from the lumbar up switch. This could be due to a complete break in the circuit (open), an unintended connection to ground (short), or a signal that falls outside the expected voltage range.
Symptoms: The most obvious symptom is the inability to adjust the lumbar support upwards. Other indicators might include intermittent operation, where the lumbar support sometimes works and sometimes doesn't. In some cases, the Check Engine Light (CEL) may illuminate, although this is less common for comfort-related features like lumbar support. The lumbar support may function correctly in other directions (down, in, out) while only the upward movement is affected.
Diagnostic Steps: A thorough diagnostic process is crucial to accurately identify the root cause of the B1840 code. Begin with a visual inspection of the wiring and connectors associated with the driver's seat and lumbar support system, looking for signs of damage, corrosion, or loose connections. Next, use a multimeter to test the driver lumbar up switch for continuity. This confirms whether the switch is properly opening and closing the circuit when pressed. Check for voltage at the switch and the SCM connector to ensure the switch is receiving power. Inspect the SCM for any visible signs of damage, such as burnt components or water intrusion. Finally, use a scan tool to monitor the switch signal data while operating the switch. This allows you to see if the SCM is receiving the correct signal from the switch.
Possible Causes: The underlying cause could stem from several issues. A faulty driver lumbar up switch is a common culprit. The switch's internal contacts may be worn or damaged, preventing it from properly completing the circuit. An open or short circuit in the wiring is another possibility. Wires can become damaged due to chafing, bending, or exposure to harsh conditions, leading to breaks or shorts. Poor electrical connections due to loose or corroded connectors can also disrupt the flow of electricity. Less frequently, the Seat Control Module (SCM) itself may be faulty. The SCM is responsible for processing the signals from the switch and controlling the lumbar support motor. In rare cases, the Body Control Module (BCM) could be the source of the problem, especially in vehicles where the BCM handles the lumbar support functions.
Possible Solutions: The appropriate solution depends on the identified cause. Replacing the faulty driver lumbar up switch is the most common fix if the switch is defective. Repairing or replacing damaged wiring or connectors is necessary if there are breaks or shorts in the circuit. Cleaning corroded connectors can improve electrical contact. If the SCM is faulty, replacing the Seat Control Module (SCM) is required. Replacing the Body Control Module (BCM) is a last resort and should only be considered if all other possibilities have been ruled out. After completing any repairs, it's crucial to clear the B1840 code using a scan tool to ensure the system is functioning correctly and that the code doesn't reappear unnecessarily.
Related Codes: The B1840 code often appears alongside other related codes indicating issues with other lumbar support functions. B1835 (Driver Lumbar Down Switch Circuit Malfunction) indicates a problem with the downward movement of the lumbar support. B1845 (Driver Lumbar Forward/In Switch Circuit Malfunction) and B1850 (Driver Lumbar Backward/Out Switch Circuit Malfunction) signify malfunctions in the forward/in and backward/out lumbar support movements, respectively. Addressing all related codes is essential for restoring complete lumbar support functionality.
Severity: While a malfunctioning lumbar support doesn't directly affect the vehicle's safety or drivability, it can significantly impact driver comfort, especially on long journeys. Persistent discomfort can lead to fatigue and reduced concentration, potentially increasing the risk of accidents. Furthermore, ignoring the issue could lead to further electrical problems as damaged wiring can short out other systems. Therefore, addressing the B1840 code promptly is recommended.
Common Vehicles Affected: The B1840 code can occur in a wide range of vehicles equipped with power-adjustable seats and lumbar support. The specific makes and models affected vary, but it is more commonly observed in vehicles with more complex seat control systems. Consulting the vehicle manufacturer's technical service bulletins (TSBs) is highly recommended. TSBs often contain valuable information about known issues and specific diagnostic procedures for particular models.
Frequently Asked Questions
What does the B1840 code mean? The B1840 code indicates a malfunction in the driver's seat lumbar support "up" switch circuit. This means the vehicle's computer has detected an issue with the electrical circuit controlling the upward movement of the lumbar support.
Can I still drive my car with the B1840 code? Yes, the code doesn't directly impact the car's drivability, but the lumbar support won't function correctly. It's advisable to fix it for comfort and to prevent potential future electrical issues.
How do I fix the B1840 code? The fix depends on the cause, but common solutions include replacing the switch, repairing wiring, or replacing the seat control module. A proper diagnosis is needed to determine the correct solution.
Is the B1840 code a serious problem? While not immediately critical, it can cause discomfort and potentially lead to further electrical problems if ignored. Addressing it promptly is recommended.
Where is the lumbar support switch located? The lumbar support switch is typically located on the side of the driver's seat, often integrated into the seat control panel. Refer to your vehicle's owner's manual for the exact location.
Conclusion
The B1840 code signals a malfunction in the driver's lumbar up switch circuit, leading to a loss of upward lumbar support adjustment. Proper diagnosis and repair are essential to restore full seat functionality and prevent potential future electrical issues. Addressing the root cause, whether it's a faulty switch, damaged wiring, or a faulty control module, will ensure driver comfort and a properly functioning seat.