Introduction:
The B2708 diagnostic trouble code (DTC) indicates a fault within the gearshift unlock circuit, specifically reporting a "high" voltage condition as detected by the Body Control Module (BCM). This circuit is crucial for allowing the driver to shift the vehicle out of the "Park" position, especially in scenarios where the brake pedal is not depressed or the ignition switch is malfunctioning. Understanding the causes, symptoms, and troubleshooting steps for the B2708 code is essential for ensuring vehicle safety and operability.
| Topic | Description | Potential Causes |
|---|---|---|
| Gearshift Unlock Circuit | The electrical circuit responsible for releasing the gearshift lever from the "Park" position. | Faulty brake light switch, defective shift lock solenoid, wiring harness issues (shorts to voltage, opens), malfunctioning Body Control Module (BCM), ignition switch problems, low battery voltage, corrosion in connectors. |
| BCM (Body Control Module) | The electronic control unit managing various body functions, including the gearshift unlock circuit. | Internal BCM failure, software glitches within the BCM, damaged connectors at the BCM, voltage spikes affecting the BCM. |
| "High" Voltage Indication | The BCM detects a voltage reading in the gearshift unlock circuit that is higher than expected. | Short to voltage in the wiring harness, a faulty component (like a diode) causing voltage backfeed, a problem within the BCM itself causing it to incorrectly interpret the voltage, aftermarket accessories improperly wired into the vehicle's electrical system. |
| Symptoms | Observable issues resulting from the B2708 code. | Inability to shift out of "Park," intermittent shifting problems, brake lights not working correctly (if related to the brake light switch), check engine light illuminated, other electrical malfunctions. |
| Troubleshooting Steps | Procedures for diagnosing and resolving the B2708 code. | Visual inspection of wiring and connectors, testing the brake light switch, checking the shift lock solenoid, testing the wiring harness for shorts and opens, scanning the BCM for other DTCs, inspecting the ignition switch, verifying battery voltage and connections. |
| Related DTCs | Other diagnostic trouble codes that might accompany B2708. | Codes related to the brake light switch, shift lock solenoid, ignition switch, BCM, or other electrical circuits. |
| Tools Required | Equipment needed for diagnosing and repairing the issue. | Multimeter, scan tool, wiring diagrams, basic hand tools, test light. |
| Repair Procedures | Steps to fix the underlying cause of the B2708 code. | Replacing faulty components (brake light switch, shift lock solenoid, BCM), repairing wiring harness damage, cleaning corroded connectors, reprogramming the BCM (if necessary). |
Detailed Explanations:
Gearshift Unlock Circuit: This circuit is designed to prevent unintentional shifting out of "Park," particularly when the vehicle is not under the driver's direct control. It typically relies on a signal from the brake light switch indicating that the brake pedal is depressed. When the brake pedal is pressed, the brake light switch sends a signal to the BCM, which then activates the shift lock solenoid, allowing the gearshift lever to be moved. The circuit includes wiring, connectors, the brake light switch, the shift lock solenoid, and the BCM.
BCM (Body Control Module): The BCM acts as a central hub for controlling various electronic functions within the vehicle's body. This includes lighting, door locks, power windows, security systems, and, importantly, the gearshift unlock mechanism. The BCM receives inputs from various sensors and switches, processes this information, and then sends signals to control different outputs. Its role in the gearshift unlock circuit is to interpret the brake light switch signal and activate the shift lock solenoid accordingly.
"High" Voltage Indication: When the BCM detects a "high" voltage in the gearshift unlock circuit, it signifies that the voltage level is exceeding the expected or normal range. This anomaly triggers the B2708 DTC. A high voltage condition can be caused by a short to voltage, where a wire in the circuit is inadvertently making contact with a power source. It could also be caused by a malfunctioning component that is feeding excessive voltage into the circuit, or by a faulty BCM misinterpreting the actual voltage.
Symptoms: The most common and noticeable symptom of the B2708 code is the inability to shift the vehicle out of "Park." This occurs because the shift lock solenoid is not being activated, preventing the gearshift lever from moving. Other potential symptoms include intermittent shifting problems, where shifting may be possible sometimes but not others. If the brake light switch is involved, the brake lights might not function correctly. The check engine light will illuminate, and other seemingly unrelated electrical malfunctions might occur as the BCM is responsible for many systems.
Troubleshooting Steps: A systematic approach is crucial for diagnosing the B2708 code. Begin with a visual inspection of the wiring and connectors associated with the gearshift unlock circuit. Look for any signs of damage, corrosion, or loose connections. Next, test the brake light switch to ensure it is functioning correctly. You can use a multimeter to check for continuity when the brake pedal is pressed. Check the shift lock solenoid to verify that it is receiving power and is functioning as expected. Test the wiring harness for shorts to voltage, shorts to ground, and opens. A scan tool can be used to scan the BCM for other DTCs, which may provide additional clues about the underlying problem. Inspect the ignition switch for any signs of malfunction. Finally, verify the battery voltage and connections to ensure that the BCM is receiving adequate power.
Related DTCs: The B2708 code may be accompanied by other DTCs that can provide valuable insights into the root cause of the problem. These may include codes related to the brake light switch, shift lock solenoid, ignition switch, BCM, or other electrical circuits. For instance, a code indicating a fault in the brake light switch circuit could suggest that the brake light switch is the source of the problem.
Tools Required: Diagnosing and repairing the B2708 code typically requires a few essential tools. A multimeter is necessary for testing voltage, continuity, and resistance in the electrical circuits. A scan tool is needed to read DTCs from the BCM and other control modules. Wiring diagrams are essential for understanding the layout of the electrical circuits and identifying the correct wires to test. Basic hand tools such as screwdrivers, pliers, and wire strippers are also required. A test light can be helpful for quickly checking for power and ground in the circuits.
Repair Procedures: The repair procedures for the B2708 code will depend on the underlying cause of the problem. If the brake light switch is faulty, it will need to be replaced. If the shift lock solenoid is defective, it will also need to be replaced. If there is damage to the wiring harness, the damaged wires will need to be repaired or replaced. If there is corrosion in the connectors, they will need to be cleaned or replaced. In some cases, the BCM itself may be faulty and require replacement or reprogramming.
Frequently Asked Questions:
What does the B2708 code mean? The B2708 code indicates a "Gearshift Unlock Circuit High" fault detected by the Body Control Module (BCM), meaning the BCM is reading a higher than expected voltage in the circuit that unlocks the gearshift.
Can I drive my car with the B2708 code? Driving might be impossible if the car is stuck in "Park," and even if it's not, it's not recommended as the underlying problem can affect other systems and potentially compromise safety.
What is the most common cause of the B2708 code? A faulty brake light switch is often the culprit, as it's a critical component in the gearshift unlock circuit.
How do I fix the B2708 code? Troubleshooting involves checking the brake light switch, shift lock solenoid, wiring harness, and BCM, followed by repairing or replacing faulty components.
Will replacing the BCM fix the B2708 code? Replacing the BCM is only necessary if it's determined to be the source of the problem after thorough testing of other components.
Conclusion:
The B2708 diagnostic trouble code signals a problem within the gearshift unlock circuit, indicating a high voltage condition as perceived by the BCM. A systematic approach to troubleshooting, including visual inspection, component testing, and wiring checks, is essential for identifying and resolving the underlying cause of the code.