Decoding OBDII Code B1644: Understanding and Resolving Rear Left Turn Control Circuit High Faults

Navigating the complexities of modern vehicle diagnostics often involves deciphering OBDII codes. Among these, code B1644, specifically “Rear Left Turn Control Circuit High,” signals a potential issue within your vehicle’s lighting system. As an auto repair expert at autelfrance.com, we’re here to provide you with a comprehensive understanding of this code, its implications, and effective troubleshooting strategies.

Understanding OBDII Code B1644

Obdii Code B1644 is categorized as a body code, indicating a problem within the vehicle’s body control systems, in this case, the lighting circuits. Specifically, “Rear Left Turn Control Circuit High” points to an abnormality in the electrical circuit responsible for powering the rear left turn signal lamp. The “High” designation suggests that the control module has detected a voltage reading in the circuit that is higher than expected under normal operating conditions.

To fully grasp this, let’s break down the key components:

• OBDII (On-Board Diagnostics II): The standardized system in vehicles that monitors and reports on various vehicle systems, including emissions, engine, transmission, and body controls.
• B Code (Body Code): Designates that the fault lies within the body control systems, which manage features like lighting, power windows, and security systems.
• 1644: A specific fault code number assigned to “Rear Left Turn Control Circuit High.”
• Rear Left Turn Control Circuit: The wiring and components that provide power and control to the rear left turn signal bulb.
• Circuit High: Indicates that the voltage in the circuit is higher than the expected range.

This code is typically triggered when the vehicle’s computer, often the Body Control Module (BCM) or Central Gateway Module, detects an unusually high voltage in the circuit controlling the rear left turn signal. This is not necessarily a complete circuit failure, but rather an anomaly that can affect the proper functioning of the turn signal.

Symptoms Associated with OBDII Code B1644

When OBDII code B1644 is present, you may observe several symptoms, which can help in pinpointing the problem:

• Rear Left Turn Signal Malfunction: This is the most direct symptom. The rear left turn signal may not illuminate at all, may blink erratically (too fast or too slow), or may be dimmer than usual.
• Warning Light on Dashboard: The vehicle’s information display or dashboard may illuminate a warning light, such as the check engine light or a specific indicator for lighting system issues.
• Other Lighting Issues (Potentially): In some cases, a “circuit high” fault in one lighting circuit can indirectly affect other lights or systems due to shared power or control modules. However, this is less common with B1644 and more likely with codes indicating module failures.
• No Noticeable Symptoms: Less frequently, the code might be logged as “temporary” or “intermittent,” meaning the fault occurred but may not be consistently present. In these cases, symptoms might be subtle or not immediately apparent.

It’s crucial to note that the absence of obvious symptoms doesn’t negate the presence of the code. A diagnostic scan is essential for accurate problem identification.

Potential Causes of OBDII Code B1644

Several factors can contribute to a “Rear Left Turn Control Circuit High” fault. Understanding these potential causes is the first step in effective troubleshooting:

• Faulty Rear Left Turn Signal Bulb: While “circuit high” suggests voltage issues, a failing bulb can sometimes cause unexpected resistance changes in the circuit, leading to incorrect voltage readings by the control module.
• Wiring Issues: This is a common culprit. Problems within the wiring harness for the rear left turn signal can include:
  • Short Circuit to Voltage: If the wiring is chafed, damaged, or improperly routed, it might be shorting to a voltage source, causing an elevated voltage reading.
  • Corrosion or Damage: Corrosion in connectors or damage to the wiring itself can increase resistance, which can sometimes be misinterpreted as a “high” voltage condition by the module.
• Connector Problems: Loose, corroded, or damaged connectors in the rear left turn signal circuit can disrupt the intended electrical flow and cause inaccurate readings.
• Body Control Module (BCM) or Central Gateway Module Failure: While less frequent than wiring or bulb issues, a malfunctioning BCM or Central Gateway Module itself can be the source of the problem. Internal module faults can lead to incorrect circuit monitoring and erroneous code setting.
• Aftermarket Lighting Modifications: Improperly installed aftermarket lighting, especially LED bulbs or modifications to the turn signal circuit, can disrupt the circuit’s electrical characteristics and trigger B1644.

Diagnosing and Resolving OBDII Code B1644

Diagnosing B1644 requires a systematic approach. Here’s a step-by-step guide for technicians:

1. Initial OBDII Scan: Use an OBDII scanner, preferably an advanced tool like Autel diagnostic scanners, to confirm the presence of code B1644 and check for any other related codes. Note down all codes and freeze frame data.
2. Visual Inspection: Thoroughly inspect the rear left turn signal bulb, socket, and wiring harness. Look for:
   • Bulb Condition: Check for a burnt-out filament or physical damage to the bulb.
   • Wiring Damage: Inspect the wiring harness for any signs of chafing, cuts, melting, or improper routing. Pay close attention to areas where wiring might rub against the vehicle’s frame or body.
   • Connector Condition: Examine the connectors for corrosion, bent pins, or loose connections. Clean and reseat connectors as needed.
3. Bulb Test: Replace the rear left turn signal bulb with a known good bulb to rule out a bulb issue. Clear the code and re-scan to see if it returns.
4. Circuit Testing with Multimeter: Use a multimeter to perform voltage and continuity tests on the rear left turn signal circuit.
   • Voltage Test: Check the voltage at the bulb socket with the turn signal activated. Compare the reading to the expected voltage (typically battery voltage). A significantly high reading can indicate a short to voltage.
   • Continuity Test: With the circuit de-energized, perform continuity tests on the wiring to check for open circuits or shorts to ground.
5. Module Diagnosis (BCM/Central Gateway): If wiring and bulb checks are inconclusive, suspect a potential module issue. Advanced diagnostic tools can perform module-level tests and checks. However, module replacement should be considered as a last resort after ruling out all other possibilities.
6. Review Vehicle-Specific Technical Service Bulletins (TSBs): Check for any TSBs related to B1644 or turn signal issues for the specific vehicle make and model. TSBs can provide valuable insights and known fixes.

Resolution Strategies:

• Bulb Replacement: If a faulty bulb is identified, replace it with the correct type and rating.
• Wiring Repair: Repair any wiring damage, including fixing shorts, opens, or corrosion. This may involve splicing wires, replacing sections of the harness, or cleaning connectors.
• Connector Repair/Replacement: Clean corroded connectors or replace damaged connectors to ensure proper circuit integrity.
• Module Replacement (BCM/Central Gateway): If module failure is confirmed after thorough diagnosis, replace and reprogram the module as necessary. Refer to vehicle-specific repair procedures for module replacement and programming.
• Correct Aftermarket Lighting Issues: If aftermarket lighting is causing the problem, revert to original equipment or ensure the aftermarket components are correctly installed and compatible with the vehicle’s electrical system.

Conclusion

OBDII code B1644, “Rear Left Turn Control Circuit High,” indicates a voltage anomaly in the rear left turn signal circuit. While it might seem like a minor lighting issue, addressing it promptly is crucial for safety and proper vehicle operation. By understanding the symptoms, potential causes, and diagnostic procedures outlined above, you can effectively troubleshoot and resolve B1644, ensuring your vehicle’s lighting system functions as intended. Remember to utilize professional-grade diagnostic tools like Autel scanners for accurate and efficient repairs. For further in-depth diagnostics and advanced troubleshooting, always consult vehicle-specific service manuals and consider seeking assistance from certified automotive technicians.