B1373

What Does Code B1373 Mean?

DTC B1373 signifies an electrical fault within the control circuit or output circuit of the Illuminated Entry Relay, specifically detecting a continuous short to battery voltage. This code is typically set by the Body Control Module (BCM) or General Electronic Module (GEM), which monitors the operational status of various interior electrical systems, including the illuminated entry system. The illuminated entry system is designed to provide temporary interior lighting (e.g., dome lights, map lights, courtesy lights) when a vehicle door is opened or upon disarming, aiding occupants in entering or exiting the vehicle. When the BCM/GEM detects an unintended, continuous supply of voltage on the relay’s control or output circuit that matches or is very close to battery voltage, even when the system is commanded off, it registers this as a “short to battery.” This condition implies that the relay’s circuit is receiving power independently of the BCM’s control, or the relay itself is internally stuck in a closed position, constantly supplying power to the lights. This abnormal voltage signal disrupts the module’s ability to properly control the interior lighting, leading to the illumination of the malfunction indicator light (MIL) or a service message.

Common Symptoms

• Interior lights (dome, map, courtesy lights) remain constantly illuminated, even with doors closed or ignition off.
• Interior lights do not turn off after the normal timed delay.
• Rapid battery discharge or parasitic draw due to continuously active lights.
• Illuminated entry system fails to operate correctly (e.g., lights never turn on or off).
• Blown fuses related to the interior lighting circuit (less common, but possible if the short causes excessive current).

What Causes the Code B1373?

• Faulty Illuminated Entry Relay: The relay itself may be internally shorted, stuck in the “on” (closed) position, or have an internal fault causing its output to remain energized, leading to a continuous supply of battery voltage to the lighting circuit.
• Wiring Harness Short to Voltage: A damaged or chafed wire in the illuminated entry relay’s control circuit or its output circuit can make unintentional contact with a constant 12-volt power source, creating a direct “short to battery.”
• Corroded or Damaged Electrical Connectors: Water intrusion or corrosion within the connectors associated with the illuminated entry relay or its wiring can bridge terminals, creating unintended conductive paths and mimicking a short to voltage.
• Faulty Body Control Module (BCM) / General Electronic Module (GEM): While less common, an internal malfunction within the BCM or GEM could cause it to incorrectly apply voltage to the relay’s control circuit, or misinterpret feedback from the circuit, leading to the detection of a short.

How to Diagnose and Troubleshoot

Diagnosis of B1373 requires a systematic approach, often involving a digital multimeter (DMM), an OBD-II scanner capable of reading BCM/GEM codes, and the vehicle’s specific wiring diagrams.

1. Verify and Clear DTC: Connect an OBD-II scanner to confirm B1373 is present. Note if it’s a current or history code. Clear the code and operate the vehicle’s illuminated entry system to see if the code immediately returns.
2. Visual Inspection: Disconnect the negative battery terminal before extensive electrical work. Visually inspect the wiring harness leading to the illuminated entry relay and the interior lighting components. Look for any signs of chafing, pinching, melting, or other physical damage. Pay close attention to areas where wiring passes through firewalls, door jambs, or under carpets. Inspect all connectors for corrosion, bent pins, or loose terminals.
3. Locate and Test the Illuminated Entry Relay: Using the vehicle’s service manual, identify the precise location of the illuminated entry relay, typically found in a fuse block (under-hood or interior).
   • Relay Functionality Test (Bench Test): With the relay removed, use a DMM to check for continuity between the switch terminals (usually 30 and 87/87a). There should be no continuity. Apply 12 volts to the coil terminals (usually 85 and 86) and listen for an audible click. While voltage is applied, recheck continuity between terminals 30 and 87 (normally open) – it should now show continuity. No click or incorrect continuity indicates a faulty relay.
   • Relay Socket Voltage Check: With the relay removed and the battery reconnected, identify the constant 12V power supply terminal in the relay socket (usually 30) using the wiring diagram and DMM. Check the control circuit terminal (from the BCM/GEM) for voltage when the illuminated entry system should be off. If battery voltage is present on this control circuit when it should be low (near 0V) or ground, the short is upstream towards the BCM/GEM or in the wiring leading to the BCM’s output. Check the output circuit terminal (to the lights, usually 87) for voltage with the relay removed and the system off. If battery voltage is present, there’s a short to power in the wiring leading to the interior lights.
4. Circuit Continuity and Short to Voltage Tests:
   • Isolate the Circuit: Disconnect the BCM/GEM connector and the relay harness connector. This isolates the wiring segment.
   • Test for Short to Voltage: Using the DMM, set to voltage mode, probe the affected wire (control circuit or output circuit) while it’s disconnected from all power sources. If any voltage is detected, there is an external short to a power source.
   • Test for Short to Ground/Continuity: While disconnected, check for continuity between the affected wire and chassis ground. Although B1373 indicates a “short to battery,” an unintended short to ground can also cause abnormal circuit behavior.
5. BCM/GEM Input/Output Test: If your scanner has bi-directional control capabilities, attempt to command the illuminated entry relay ON and OFF through the BCM/GEM. Monitor the associated live data PIDs (Parameter IDs) for the relay’s status and voltage. This can help confirm if the BCM/GEM is attempting to control the relay correctly or if it’s misinterpreting feedback.

Recommended Repairs and Solutions

Once the root cause of B1373 has been precisely identified through methodical diagnosis, the following repairs are typically recommended:

• Replace the Faulty Illuminated Entry Relay: If the relay fails the bench tests or socket voltage checks indicate it’s stuck closed or internally shorted, replace it with a new OEM-equivalent part. Ensure the new relay matches the specifications of the original.
• Repair or Replace Damaged Wiring: If a short to voltage in the wiring harness is identified, carefully repair the damaged section. Use appropriate soldering techniques, heat-shrink tubing, and secure the repair to prevent future damage. If the damage is extensive or in an inaccessible area, consider replacing the entire affected wiring harness segment.
• Clean or Replace Corroded Connectors: If corrosion is found in any electrical connectors, use an electrical contact cleaner and a small brush to thoroughly clean the terminals. Inspect for any bent or damaged pins and repair or replace the connector as necessary. Apply dielectric grease to prevent future corrosion.
• Replace the Body Control Module (BCM) / General Electronic Module (GEM): This should be a last resort, only performed after all other components and wiring have been meticulously tested and confirmed to be in good working order. BCM/GEM replacement often requires programming or “flashing” to the vehicle’s specific VIN, which typically necessitates dealer-level diagnostic equipment. Always ensure all other possibilities are exhausted before condemning the BCM/GEM.
• Important Mechanics’ Tips:
  • Always disconnect the battery’s negative terminal before performing any electrical repairs to prevent accidental shorts or damage to sensitive electronic components.
  • Refer to the vehicle-specific factory service manual for accurate wiring diagrams, component locations, and diagnostic procedures.
  • After any electrical repair, clear the DTCs and perform a functional test of the illuminated entry system to ensure the issue is resolved and the code does not return.
  • When replacing fuses, always use a fuse of the correct amperage rating. Using an incorrect fuse can lead to further electrical damage or fire.