B1392

What Does Code B1392 Mean?

DTC B1392 signifies a detected malfunction within the control circuit for the power door memory lock relay. This code is typically set by a Body Control Module (BCM), Door Control Module (DCM), or a similar General Electronic Module (GEM) rather than the Powertrain Control Module (PCM), as it pertains to a body electrical system. The implicated relay is integral to the vehicle’s power door lock system, often specifically integrated with driver-specific memory functions for features like seat position, mirror settings, and personalized door lock behavior. The control module monitors the electrical parameters (voltage, current, resistance) of the relay’s control circuit. When the module detects an electrical anomaly such as an open circuit (excessive resistance), a short to ground (insufficient resistance), a short to voltage (unexpected voltage), or an out-of-specification current draw, it interprets this as a “circuit failure” and logs code B1392.

Common Symptoms

• Inoperative Power Door Locks: Doors may fail to lock or unlock using the interior switches or the remote key fob.
• Intermittent Lock Operation: Power locks may work erratically, sometimes operating and sometimes failing.
• Memory Function Malfunction: Door locks may not respond correctly when recalling specific driver profiles or memory settings.
• Security System Anomalies: In some vehicles, a related issue might trigger a “Door Ajar” warning or affect the functionality of the vehicle’s security system.
• Parasitic Battery Drain: In rare cases, a shorted or partially stuck relay could lead to continuous power draw, resulting in a drained battery.

What Causes the Code B1392?

• Faulty Power Door Memory Lock Relay: The relay itself may have internal failures such as a stuck contact, an open coil, or a short circuit.
• Wiring Harness Damage: An open circuit, short to ground, or short to voltage in the wiring connecting the control module to the relay, or the relay to the door lock actuators. This often occurs in areas subject to movement, such as door jambs.
• Corroded or Loose Electrical Connections: Poor contact at the relay socket, connector pins, or ground points within the relay’s circuit can lead to high resistance or intermittent connectivity.
• Failed Control Module (BCM/DCM): The electronic module responsible for commanding the relay may have an internal fault, preventing it from sending the correct control signal or properly monitoring the relay’s circuit.
• Faulty Door Lock Actuator(s): Although the code points to the relay circuit, an actuator drawing excessive current or experiencing an internal short could overload the relay circuit, leading the control module to detect an anomaly.

How to Diagnose and Troubleshoot

Diagnosis of B1392 requires a systematic approach using a digital multimeter (DMM), an OBD-II scanner capable of reading B-codes, and vehicle-specific wiring diagrams.

1. Retrieve and Analyze DTCs and Freeze Frame Data: Connect an OBD-II scanner to the vehicle’s DLC. Retrieve all current and pending DTCs, focusing on any B-codes. Note any freeze frame data, as it provides a snapshot of system conditions when the code was set.
2. Locate the Power Door Memory Lock Relay: Consult the vehicle’s service manual or wiring diagrams to pinpoint the exact location of the power door memory lock relay and its associated fuse(s). This location varies significantly by manufacturer and model.
3. Perform a Thorough Visual Inspection: Carefully inspect all visible wiring and connectors related to the power door lock system, the control module (BCM/DCM), and specifically the relay’s circuit. Look for signs of chafing, cuts, corrosion, bent pins, or loose connections. Pay particular attention to wiring that passes through door jambs, which is prone to fatigue.
4. Check Associated Fuses: Using a DMM set to continuity or ohms, test all fuses identified in the wiring diagram as protecting the power door lock system and the relay circuit. Replace any blown fuses, but be aware that a recurring blown fuse indicates a short circuit that must be found and rectified.
5. Test the Relay Circuit with DMM:
   • Power Input: With the ignition ON, identify the relay’s constant battery voltage terminal (often pin 30) using the wiring diagram. Use the DMM to verify battery voltage present at this terminal in the relay socket.
   • Control Signal: Identify the relay’s control coil terminals (often pins 85 and 86). With the relay removed, use the DMM to check for the appropriate voltage or ground signal from the BCM/DCM when the door locks are commanded (e.g., using the remote or interior switch). If no signal is present, the issue could be the control module or its input.
   • Output Circuit: If possible to safely jumper the relay, or with the relay installed and commanded ON, check for battery voltage at the relay’s output terminal (often pin 87) leading to the door lock actuators.
6. Bench Test the Relay: Remove the relay. Apply 12V and ground to the relay’s control coil terminals (usually 85 and 86). Listen for an audible “click” indicating the coil is activating. Then, use the DMM to check for continuity across the switch terminals (usually 30 and 87). Continuity should be present only when the control coil is energized. If it fails, the relay is faulty.
7. Wiring Continuity and Short Test: Disconnect the vehicle’s battery. Disconnect the BCM/DCM connector and the relay connector. Use the DMM to check for continuity (near 0 ohms) in each wire segment of the relay’s control and power circuits. Also, check for unintended shorts to ground (near 0 ohms to chassis ground) or shorts to power (near 0 ohms to a known battery positive source) on all wires. Compare readings to manufacturer specifications for acceptable resistance.
8. Inspect Door Lock Actuators: If the relay and its immediate wiring test good, inspect the door lock actuators. While B1392 points to the relay, a shorted actuator can cause an overload. Check actuator resistance if specified in the service manual, and consider testing their current draw if possible.

Recommended Repairs and Solutions

Once the root cause of B1392 has been precisely identified through systematic diagnosis, the following repairs are typically recommended:

1. Replace Faulty Power Door Memory Lock Relay: If the relay failed any of the diagnostic tests, replace it with a new, OEM-specified or equivalent quality relay. Ensure the new relay has the correct electrical specifications and pin configuration.
2. Repair or Replace Damaged Wiring: If wiring harness damage (chafing, cuts, opens, or shorts) is identified, perform professional wiring repair. This involves cutting out the damaged section, soldering in new wire of the correct gauge and type, and insulating with heat-shrink tubing. For extensive damage, replacing the entire harness segment may be necessary. Pay critical attention to wiring at the door hinges or jambs, as these areas are prone to repeated stress.
3. Clean and Secure Electrical Connections: If corrosion or loose terminals are found, meticulously clean the affected connectors and terminals using an appropriate electrical contact cleaner and a small brush. Ensure all connectors are fully seated and latched. Apply dielectric grease to prevent future corrosion.
4. Replace Faulty Control Module (BCM/DCM): If all other components (wiring, fuses, relay, actuators) test good and the control module is not providing the correct command signals or accurately monitoring the circuit, the module itself may be defective. Module replacement often requires specialized programming or calibration by a dealership or a shop equipped with appropriate diagnostic tools.
5. Replace Faulty Door Lock Actuator(s): If an actuator was found to be the underlying cause of an overload or short in the relay circuit, replace the faulty actuator(s).

After any repair, clear the DTCs using an OBD-II scanner. Operate the power door locks multiple times (both manually and via memory functions) to confirm proper operation and ensure the code does not return before returning the vehicle to service.