B0748 - D (drive) Indicator Circuit High (BCM)

Introduction:

The diagnostic trouble code (DTC) B0748 indicates a problem with the circuit controlling the "D" (Drive) indicator light, specifically within the Body Control Module (BCM). This code suggests that the BCM is detecting an abnormally high voltage in the circuit responsible for illuminating the "D" indicator on the instrument panel when the vehicle is in Drive. Understanding the causes and troubleshooting steps for this code is crucial for maintaining proper vehicle operation and driver awareness.

Comprehensive Table: B0748 - D (Drive) Indicator Circuit High (BCM)

Detailed Explanations:

Code Definition (B0748): This is the specific code assigned to indicate a "D (Drive) Indicator Circuit High (BCM)" fault. The BCM has detected an abnormal voltage in the circuit responsible for illuminating the "D" indicator.

Affected System (Transmission Indication): This code directly relates to the system responsible for visually indicating to the driver that the vehicle is in the "Drive" gear. This indication is crucial for safe and informed vehicle operation.

Root Cause Category (Electrical Circuit Fault): The underlying problem is an electrical issue within the indicator circuit. This means there is a problem with voltage, current, resistance, or connectivity within the circuit.

Common Causes:

• Short to Voltage: A wire in the "D" indicator circuit is unintentionally making contact with a voltage source, causing the BCM to read a higher than expected voltage. This often happens when insulation is damaged and a wire rubs against metal.
• Open Circuit: A break in the wiring prevents the current from flowing properly through the "D" indicator circuit. This could be a broken wire, a loose connector, or a corroded terminal.
• High Resistance: Corrosion or damage in the circuit is impeding the flow of current, creating excessive resistance. This can cause the voltage to be elevated at the BCM.
• Faulty BCM: The Body Control Module itself could be malfunctioning internally, misinterpreting the signals from the "D" indicator circuit or sending incorrect signals to the indicator.
• Faulty Indicator Bulb/LED: While less common, a failing bulb or LED can sometimes cause unexpected voltage readings in the circuit, triggering the B0748 code.
• Wiring Harness Damage: Physical damage to the wiring harness, such as cuts, abrasions, or rodent damage, can disrupt the circuit's integrity.
• Connector Corrosion: Corrosion within the connectors in the "D" indicator circuit can lead to high resistance or even an open circuit, causing the B0748 code.

Symptoms:

• "D" Indicator Constantly On: The "D" indicator light remains illuminated even when the vehicle is not in Drive. This is a common symptom of a short to voltage.
• "D" Indicator Not Illuminating: The "D" indicator light fails to light up when the vehicle is in Drive. This is often caused by an open circuit or a faulty bulb/LED.
• Intermittent "D" Indicator Operation: The "D" indicator may work sporadically, turning on and off at random. This can be due to a loose connection or intermittent short.
• Other Indicator Lights Malfunctioning: In some cases, other indicator lights controlled by the BCM may also exhibit problems, indicating a potential issue with the BCM itself.
• No Noticeable Symptoms: Sometimes, the only symptom is the presence of the B0748 DTC in the vehicle's computer system.

Diagnostic Tools:

• Scan Tool: A scan tool is necessary to retrieve the B0748 DTC from the vehicle's computer. It can also be used to clear the code after repairs are made.
• Multimeter: A multimeter is essential for testing the voltage, resistance, and continuity of the "D" indicator circuit. This tool helps pinpoint the location of electrical faults.
• Wiring Diagram: A vehicle-specific wiring diagram is crucial for tracing the "D" indicator circuit and identifying the correct wires and connectors to test.

Troubleshooting Steps:

• Visual Inspection: Carefully inspect the wiring harnesses, connectors, and the "D" indicator bulb/LED for any signs of damage, corrosion, or loose connections. Pay close attention to areas where the wiring harness may rub against metal.
• Circuit Testing: Using a multimeter and the wiring diagram, test the continuity and voltage of the "D" indicator circuit. Check for shorts to ground, shorts to voltage, and open circuits.
• BCM Testing: Testing the BCM typically requires specialized equipment and knowledge. It is often best left to a qualified technician.
• Component Testing: Test the "D" indicator bulb/LED itself to ensure it is functioning correctly. Replace the bulb/LED if it is defective.

Potential Solutions:

• Repair Damaged Wiring: Repair or replace any damaged or frayed wires in the "D" indicator circuit. Use proper splicing techniques and ensure the repairs are well-insulated.
• Clean Corroded Connectors: Clean or replace corroded connectors to ensure good electrical contact. Use electrical contact cleaner to remove corrosion.
• Replace Faulty Indicator Bulb/LED: Replace the "D" indicator bulb/LED if it is defective. Ensure you use the correct bulb/LED type for your vehicle.
• Replace Faulty BCM: If all other troubleshooting steps fail, the Body Control Module may be faulty and need to be replaced. Note: BCM replacement often requires programming to match the vehicle's VIN and options.

Severity:

The severity of a B0748 code is generally considered low to medium. While it does not directly affect the vehicle's drivability, it can be a nuisance and potentially indicate a more significant underlying electrical issue. Ignoring the code could lead to further electrical problems.

Related DTCs:

• Other BCM related codes: If other BCM codes are present along with B0748, it could indicate a more widespread issue with the BCM itself.
• Transmission related codes: In rare cases, problems with the transmission range sensor can mimic symptoms related to the "D" indicator.

BCM Location:

The location of the BCM varies depending on the vehicle make and model. It is typically located under the dashboard, in the center console, or behind the glove box. Consult a vehicle-specific repair manual for the exact location.

Wiring Diagram Source:

A vehicle-specific repair manual or online repair database (like Alldata or Mitchell OnDemand) is the best source for accurate wiring diagrams.

Indicator Type:

The "D" indicator can be either a traditional incandescent bulb or an LED (Light Emitting Diode). Older vehicles typically use bulbs, while newer vehicles often use LEDs.

Potential for Misdiagnosis:

Problems with the transmission range sensor can sometimes mimic symptoms related to the "D" indicator. Therefore, it's crucial to perform a thorough diagnosis to rule out other potential causes.

Programming Requirements (BCM Replacement):

Whether or not BCM replacement requires programming depends on the vehicle make and model. Some BCMs require programming to match the vehicle's VIN and options, while others do not. Consult a qualified technician or refer to the vehicle-specific repair manual.

Impact on Vehicle Safety:

The impact on vehicle safety is minimal. The "D" indicator primarily assists the driver in confirming the selected gear. However, a malfunctioning indicator can be confusing or distracting.

Frequently Asked Questions:

• What does the B0748 code mean? The B0748 code indicates a problem with the "D" (Drive) indicator circuit, specifically a high voltage reading detected by the Body Control Module (BCM).

• Can I drive my car with the B0748 code? Yes, you can usually drive your car, as the code typically doesn't affect drivability, but it's best to address the issue to avoid potential electrical problems.

• What are the common causes of the B0748 code? Common causes include a short to voltage, open circuit, high resistance in the D indicator circuit, a faulty BCM, or a faulty indicator bulb/LED.

• How do I fix the B0748 code? Fixing the code involves diagnosing the circuit, repairing damaged wiring, cleaning corroded connectors, replacing faulty components, or, in some cases, replacing the BCM.

• Do I need a mechanic to fix the B0748 code? Simple fixes, such as replacing a bulb or cleaning a connector, can be done yourself, but more complex electrical issues or BCM replacement may require a qualified mechanic.

Conclusion:

The B0748 code signals a problem within the "D" indicator circuit, typically stemming from electrical faults. Thorough diagnosis and systematic troubleshooting are essential to pinpoint the root cause and implement the appropriate repair, ensuring proper vehicle operation and driver awareness.