B1310

What Does Code B1310 Mean?

DTC B1310 indicates a malfunction within the power door unlock circuit, as detected by the vehicle’s Body Control Module (BCM) or a similar integrated control unit such as a Smart Junction Box (SJB) or General Module (GM). This code specifically signifies that the control module monitoring the door lock system has identified an electrical anomaly in the circuit responsible for commanding the door lock actuators to the unlocked position. The BCM continuously monitors the electrical characteristics (voltage, current, resistance) of the door lock actuator circuits. When an out-of-specification condition is detected—such as an open circuit (excessive resistance, no current flow), a short to ground (excessive current draw, voltage drop), or a short to voltage (unintended voltage presence)—it interprets this as a failure and stores B1310. This directly impacts the ability of the vehicle’s power door lock system to unlock one or more doors, either via the interior power switch, exterior key fob (Remote Keyless Entry – RKE), or other integrated systems.

Common Symptoms

• Inability to Unlock Doors Electronically: The primary symptom is the failure of one or more power door locks to unlock when commanded by the interior switch or remote key fob.
• Intermittent Door Lock Operation: Doors may sometimes unlock, but fail intermittently, often worsening with temperature changes or vibrations.
• No Audible Click from Door Actuator: When attempting to unlock the door, there may be no sound of the actuator engaging or disengaging within the door panel.
• Remote Keyless Entry (RKE) Malfunction: While the RKE system might still function for locking, the unlock function specific to the affected door(s) will not respond.
• Security System Warning Light: In some vehicles, a related security system warning light or message may illuminate on the instrument cluster if the door lock issue impacts the vehicle’s anti-theft functions.

What Causes the Code B1310?

• Faulty Door Lock Actuator: The most common cause, where the internal motor, solenoid, or electrical contacts within the door lock actuator itself fail, creating an open circuit, a short, or becoming mechanically seized.
• Damaged Wiring Harness: Wires leading to the door lock actuator, especially where they flex through the door jamb, are prone to chafing, breaking, or shorting due to repeated opening and closing of the door. Internal wiring within the door panel can also be damaged.
• Corroded Electrical Connectors: Moisture ingress can cause corrosion in multi-pin connectors at the door jamb, inside the door panel (actuator, switch), or at the Body Control Module (BCM), leading to high resistance or intermittent connections.
• Faulty Door Unlock Switch: The interior door unlock switch can develop internal faults, such as stuck contacts, open circuits, or shorts, sending incorrect or no signals to the BCM.
• Failed Body Control Module (BCM): While less common, an internal component failure within the BCM’s driver circuit responsible for controlling the door unlock function can directly cause this code.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is crucial for B1310:

1. Retrieve and Document DTCs: Connect an advanced OBD-II scanner capable of accessing Body Control Module (BCM) data. Confirm B1310 is present and note any related codes (e.g., other door lock codes, communication codes). Note freeze frame data if available. Clear codes and re-test to see if B1310 immediately returns upon attempting to unlock the door.
2. Visual Inspection of Wiring and Connectors:
   • Begin by meticulously inspecting the wiring harness where it passes from the vehicle body into the affected door(s). Look for signs of chafing, cuts, pinching, or severe bends.
   • Carefully disconnect and inspect all electrical connectors associated with the affected door lock system: at the door jamb, within the door panel (actuator, switch), and at the BCM. Look for corrosion, bent pins, pushed-out terminals, or loose connections. Clean any corrosion with electrical contact cleaner and a small brush.
3. Functional Test and Audible Check: While attempting to unlock the door (using the interior switch or key fob), listen closely at the door panel for any audible click or whirring sound from the door lock actuator. The absence of sound suggests either no power is reaching the actuator or the actuator itself is faulty.
4. Digital Multimeter (DMM) Testing:
   • Voltage Drop Test at Actuator: With the door panel removed and access to the door lock actuator connector, identify the power and ground wires for the unlock function. Use a DMM to measure voltage present at the actuator connector when the unlock command is given. A reading significantly lower than battery voltage (e.g., less than 10-11VDC) indicates excessive resistance or an open circuit upstream in the wiring.
   • Continuity Test of Wiring: With the actuator and BCM/door switch connectors disconnected, use the DMM in continuity or resistance mode to test the integrity of the wiring from the BCM/switch to the actuator. An “OL” (open line) reading indicates a broken wire. Also, test for unintentional continuity to ground and to battery voltage on the unlock signal wire(s) to detect shorts.
   • Actuator Resistance Test: Disconnect the door lock actuator and measure its internal resistance across its power/ground terminals (if applicable, consult service manual for pinout). Compare the reading to manufacturer specifications. An extremely high (open) or very low (short) resistance indicates an internally failed actuator.
   • Door Unlock Switch Test: Test the continuity or resistance of the door unlock switch while actuating it. Ensure it correctly opens and closes the circuit and that its resistance is within specification when activated.
5. Pinpoint Test (Intermittent Issues): If the issue is intermittent, gently manipulate the wiring harness in the door jamb area while repeatedly commanding the door lock to unlock. If the operation temporarily restores or changes, it strongly indicates a wiring fault in that specific flex area.
6. BCM Power and Ground Verification: Before condemning the BCM, always verify that the BCM itself has proper power and ground supply circuits according to the vehicle’s wiring diagrams.

Recommended Repairs and Solutions

Once the root cause is identified through diligent diagnosis, the following repairs are typically performed:

• Repair or Replace Damaged Wiring: If damaged wiring is found, especially in the door jamb, it is imperative to repair it using high-quality automotive-grade crimp connectors and heat-shrink tubing. Soldering should be avoided in flex zones unless specifically recommended by the manufacturer. If damage is extensive, consider replacing the entire affected section of the wiring harness. Ensure the repaired wiring has adequate slack and strain relief to prevent future failure.
• Clean or Replace Corroded Connectors: If corrosion is identified, clean the connector terminals thoroughly using specialized electrical contact cleaner and a fine-bristle brush. Apply dielectric grease to the terminals before reassembly to prevent future moisture intrusion and corrosion. If terminals are severely corroded, bent, or broken, the connector body or individual terminals should be replaced.
• Replace Faulty Door Lock Actuator: This is a very common repair. If DMM testing confirms the actuator is internally faulty, it must be replaced. Ensure the new actuator is of equivalent quality to the original. During replacement, inspect and ensure all mechanical linkages are properly connected and move freely without binding. Lubricate moving parts with appropriate lubricant (e.g., white lithium grease) if necessary.
• Replace Faulty Door Unlock Switch: If the interior door unlock switch is found to be defective, replace the switch assembly. These are often integrated into the door panel trim or armrest and may require careful removal of interior trim.
• Replace Body Control Module (BCM): This should always be considered a last resort after thoroughly ruling out all other possibilities. BCM replacement is often expensive and requires specific programming or coding to the vehicle using specialized diagnostic tools (e.g., dealership scan tools) to ensure proper communication and function with other vehicle systems. Ensure all power and ground circuits to the BCM are verified correct before condemning the module.