Introduction:
The B2628 diagnostic trouble code (DTC) indicates a malfunction within the display dimming circuit of a vehicle. Specifically, it points to a "Display Dimming Pulse Width Modulation (PWM) Output Circuit High" condition, as detected by the Body Control Module (BCM). This means the BCM is reading a voltage level on the PWM output circuit that is higher than expected, suggesting a potential short circuit or component failure within the dimming system. Addressing this code promptly is crucial for restoring proper display brightness control and preventing potential electrical damage.
| Category | Description | Possible Causes |
|---|---|---|
| Code Definition | Display Dimming Pulse Width Modulation (PWM) Output Circuit High (BCM) | Internal BCM fault, short to voltage in the PWM circuit, open circuit in the PWM circuit, faulty display module, wiring harness damage, poor connections |
| System Affected | Display Dimming System, Body Control Module (BCM) | Affects instrument panel brightness, infotainment screen brightness, and potentially other interior lighting controlled by PWM dimming. |
| PWM Signal Characteristics | Pulse Width Modulation (PWM) is used to control brightness. The duty cycle (percentage of time the signal is high) determines the brightness level. A higher duty cycle corresponds to higher brightness. | A "high" condition indicates the PWM signal is stuck at a high voltage level, preventing proper dimming. This could be due to a short to voltage, a failed PWM driver within the BCM, or a fault within the display module itself. |
| Possible Symptoms | Display stuck at maximum brightness, inability to dim the display, intermittent display brightness, battery drain (in severe cases), BCM malfunction. | Dim or no display, intermittent display, complete failure, other BCM related issues |
| Diagnostic Steps | Visual inspection of wiring and connectors, voltage and continuity testing of the PWM circuit, BCM testing, display module testing, component replacement. | Use a multimeter to check for shorts to ground or voltage on the PWM signal wire. Verify the integrity of the wiring harness and connectors. Use a scan tool to monitor the PWM signal and look for anomalies. Consult the vehicle's service manual for specific testing procedures. |
| Related Components | Body Control Module (BCM), Display Module (Instrument Panel, Infotainment Screen), Dimmer Switch, Wiring Harness, Connectors, Fuses | BCM controls the PWM signal, the Display Module receives the PWM signal, the Dimmer switch is an input to the BCM, wiring and connectors transmit the signal, and fuses protect the circuit. |
| Severity | Moderate to High | Can lead to driver distraction due to excessive brightness, battery drain, and potential BCM damage. |
| Common Tools Required | Multimeter, Scan Tool, Wiring Diagram, Test Light | A multimeter is essential for voltage and continuity testing. A scan tool allows you to read DTCs and monitor live data. A wiring diagram helps you trace the circuit. A test light can be used for basic voltage checks. |
Detailed Explanations
Code Definition: Display Dimming Pulse Width Modulation (PWM) Output Circuit High (BCM)
This code, B2628, signifies that the vehicle's Body Control Module (BCM) has detected an abnormally high voltage on the output circuit responsible for controlling the brightness of the display using Pulse Width Modulation (PWM). The BCM monitors the voltage level on this circuit, and when it exceeds a predefined threshold, the B2628 code is triggered. This situation prevents the proper dimming of the display.
System Affected: Display Dimming System, Body Control Module (BCM)
The primary system affected is the display dimming system, which includes the instrument panel display, infotainment screen, and potentially other interior lighting that utilizes PWM for brightness control. The BCM plays a central role in this system, as it generates the PWM signal that dictates the brightness level. When the B2628 code is present, the BCM's ability to accurately control the display brightness is compromised, and the fault can also damage the BCM itself.
PWM Signal Characteristics:
Pulse Width Modulation (PWM) is a technique used to control the amount of power delivered to a device by varying the "duty cycle" of a square wave signal. The duty cycle is the percentage of time the signal is "high" (on) compared to the total cycle time. For display dimming, a higher duty cycle corresponds to a brighter display, while a lower duty cycle results in a dimmer display. The B2628 code indicates that the PWM signal is stuck in a "high" state, meaning the voltage is consistently high, preventing the BCM from dimming the display.
Possible Symptoms:
The most common symptom is that the display remains at maximum brightness regardless of dimmer switch settings. Other symptoms may include:
- Inability to dim the display, causing eye strain, especially at night.
- Intermittent display brightness, where the display flickers or changes brightness unexpectedly.
- In severe cases, a potential battery drain if the high voltage condition is sustained.
- Possible BCM malfunction or other related codes.
Diagnostic Steps:
A systematic approach is crucial for accurately diagnosing the B2628 code:
- Visual Inspection: Begin by inspecting the wiring harness and connectors associated with the display dimming circuit, the dimmer switch, the display module, and the BCM. Look for signs of damage, corrosion, or loose connections.
- Voltage and Continuity Testing: Use a multimeter to measure the voltage and continuity of the PWM circuit. Check for shorts to ground or voltage on the PWM signal wire. Compare readings to the vehicle's service manual specifications.
- BCM Testing: Use a scan tool to monitor the PWM signal and look for anomalies. The scan tool can also be used to perform output tests on the BCM to verify its functionality.
- Display Module Testing: If the wiring and BCM appear to be functioning correctly, the display module itself may be faulty. Testing the display module may require specialized equipment and procedures, as outlined in the service manual.
- Component Replacement: Based on the diagnostic findings, replace any faulty components, such as the BCM, display module, or dimmer switch.
Related Components:
Several components are directly involved in the display dimming system:
- Body Control Module (BCM): The BCM generates the PWM signal that controls the display brightness.
- Display Module (Instrument Panel, Infotainment Screen): The display module receives the PWM signal and adjusts its brightness accordingly.
- Dimmer Switch: The dimmer switch provides an input to the BCM, allowing the driver to adjust the desired brightness level.
- Wiring Harness and Connectors: These components provide the electrical connections between the various components in the system.
- Fuses: Fuses protect the circuit from overcurrent conditions.
Severity:
The severity of the B2628 code can range from moderate to high. At a minimum, it results in driver distraction due to the inability to dim the display, especially during nighttime driving. In more severe cases, it can lead to battery drain or even damage the BCM, requiring costly repairs.
Common Tools Required:
Having the right tools is essential for diagnosing and repairing the B2628 code:
- Multimeter: Used for measuring voltage, continuity, and resistance.
- Scan Tool: Used for reading DTCs, monitoring live data, and performing output tests.
- Wiring Diagram: Provides a visual representation of the electrical circuits.
- Test Light: Used for basic voltage checks.
Frequently Asked Questions
What does the B2628 code mean? It means the Body Control Module (BCM) has detected a high voltage on the output circuit used to control display dimming via PWM.
Can I drive my car with the B2628 code? Yes, but the display will likely be stuck at maximum brightness, which can be distracting, especially at night.
Is the B2628 code easy to fix? The difficulty depends on the root cause; a loose connection is easier to fix than a faulty BCM.
Will replacing the dimmer switch fix the B2628 code? Possibly, but it's more likely to be a short to power in the circuit or a faulty BCM. Diagnosis is key.
How do I check for a short to voltage in the PWM circuit? Use a multimeter to measure the voltage on the PWM signal wire with the circuit disconnected from the BCM and compare to ground.
Conclusion
The B2628 code indicates a problem within the display dimming system, specifically a high voltage on the PWM output circuit. Thorough diagnosis, starting with visual inspection and progressing to voltage and continuity testing, is crucial for identifying the root cause and restoring proper display brightness control. Addressing this issue promptly will prevent driver distraction and potential damage to the vehicle's electrical system.