B1374

What Does Code B1374 Mean?

DTC B1374 signifies an issue within the vehicle’s illuminated entry system, specifically indicating a short to ground condition within the circuit controlling the Illuminated Entry Relay. This code is typically registered by the Body Control Module (BCM) or, in some vehicle architectures, the General Electronic Module (GEM), which is responsible for supervising various body electrical functions, including interior lighting and convenience features. The illuminated entry system is designed to activate interior lights, and sometimes exterior courtesy lights, upon actions such as unlocking the vehicle with a remote fob or opening a door. When the BCM/GEM detects an abnormally low resistance path, or a direct connection to chassis ground, on the control or power supply side of the Illuminated Entry Relay, it registers B1374. This short circuit can lead to the relay being constantly energized, an excessive current draw, or a complete system malfunction, as the module interprets the unexpected ground connection as a circuit fault preventing proper operation or indicating a persistent activation state.

Common Symptoms

• Interior Lights Remain On: The most prevalent symptom is the interior dome lights, map lights, or footwell lights remaining illuminated constantly, even when doors are closed and the vehicle is off or locked.
• Rapid Battery Drain: Due to the constant illumination of lights or the relay being continuously energized, an excessive parasitic current draw can occur, leading to a discharged or dead battery, particularly after the vehicle has been parked for several hours.
• Illuminated Entry System Malfunction: The system may fail to operate as designed, meaning interior lights may not turn on when expected (e.g., when unlocking the doors or opening them), or they may not respond to manual controls.
• Warning Lights on Instrument Cluster: While primarily a B-code (Body code), the BCM/GEM may trigger an associated warning light on the instrument cluster, such as a “Check System” or “Electrical Fault” indicator, though not typically the Check Engine Light (CEL).
• Clicking from Relay: In some cases, if the short is intermittent or borderline, the relay itself may be heard clicking erratically as the BCM attempts to cycle it.

What Causes the Code B1374?

• Faulty Illuminated Entry Relay: An internal short circuit within the relay itself, where the coil or contact terminals are shorted to the relay’s ground path or casing, causing the BCM to detect a continuous ground.
• Damaged Wiring Harness: Chafed, pinched, or abraded wiring leading to the Illuminated Entry Relay, resulting in direct contact between the relay’s control or power wire and the vehicle’s chassis ground. This can occur in areas prone to movement, vibration, or sharp edges.
• Corroded Relay Socket or Connector: Oxidation or moisture ingress into the relay socket or its associated connector can create a conductive path between relay terminals and ground, mimicking a short circuit.
• Improperly Installed Aftermarket Accessories: Incorrect wiring or splicing of aftermarket electrical components (e.g., alarm systems, entertainment systems, auxiliary lighting) into the illuminated entry circuit can introduce a short to ground.
• Faulty Body Control Module (BCM) or General Electronic Module (GEM): Although less common, an internal short within the BCM/GEM’s driver circuit for the Illuminated Entry Relay can cause a persistent short to ground signal, even when the external circuit is intact.

How to Diagnose and Troubleshoot

A systematic diagnostic approach is crucial for accurately resolving B1374:

1. Retrieve and Document DTCs: Use an OBD-II diagnostic scan tool to confirm B1374. Check for any related codes and review freeze frame data, which provides operating conditions when the code was set. Clear the code and attempt to replicate the fault.
2. Perform a Thorough Visual Inspection:
   • Locate the Illuminated Entry Relay. Consult the vehicle’s service manual or fuse box diagram for its precise location (often in an under-dash fuse box, under-hood power distribution center, or BCM module itself).
   • Inspect the relay and its associated connector for signs of physical damage, corrosion, melted plastic, or loose terminals.
   • Carefully inspect the wiring harness leading to the relay for any signs of chafing, pinching, or damage, particularly where it passes through bulkheads or near moving parts. Look for evidence of aftermarket modifications.
3. Relay Testing:
   • With the ignition OFF and the relay removed, use a digital multimeter (DMM) to test the relay’s coil resistance across its control terminals (typically 85 and 86). Compare the reading to service manual specifications (usually in the range of 60-120 ohms). An open circuit (OL) indicates a broken coil, while a significantly lower-than-specified resistance could indicate an internal short.
   • Apply 12V and ground to the relay’s coil terminals (85 and 86) from a fused power source. Listen for a distinct click. Then, use the DMM to check for continuity across the switch terminals (typically 30 and 87). If the relay clicks but does not show continuity, the internal contacts are faulty. If it doesn’t click, the coil is faulty.
   • Alternatively, if an identical, known-good relay is available for a non-critical function (e.g., horn relay, fog light relay), swap them to see if the symptom changes or the code transfers.
4. Circuit Integrity Testing (with DMM):
   • With Relay Disconnected: Locate the relay’s control wire terminal (often pin 86 or the ground-side trigger from the BCM). With the ignition OFF and the BCM/GEM still connected, set the DMM to resistance (Ohms) and check for continuity between this terminal and chassis ground. There should be infinite resistance (OL). Any reading approaching 0 Ohms indicates a direct short to ground in the wiring or BCM/GEM driver circuit.
   • Power Supply Check: Identify the constant 12V power supply to the relay (pin 30). With the ignition ON, check for 12V relative to chassis ground using the DMM.
   • Load Side Check: Identify the switched power output from the relay (pin 87). With the relay removed and the ignition OFF, check for continuity between this terminal and chassis ground. This should be infinite resistance (OL). A low resistance reading would indicate a short in the circuit downstream of the relay (e.g., to the interior lights).
5. Parasitic Draw Test: If interior lights are intermittently staying on or battery drain is suspected, perform a parasitic draw test using an ammeter. Connect the ammeter in series with the negative battery cable. With all vehicle systems off and doors closed, wait for modules to go to sleep (typically 20-30 minutes). Compare the current draw to manufacturer specifications (usually under 50mA). If the draw is high, systematically remove fuses, starting with the BCM/GEM or interior lighting circuits, to isolate the excessive draw.
6. Wiring Diagram Analysis: Always refer to the specific vehicle’s wiring diagrams to correctly identify terminal numbers, wire colors, and circuit paths for the Illuminated Entry Relay and its BCM/GEM control.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace the Illuminated Entry Relay: If diagnostic tests confirm the relay itself is faulty (internal short, open coil, or failed contacts), replace it with a new, OEM-specified relay. Ensure the new relay has the correct pin configuration and current rating.
• Repair or Replace Damaged Wiring: If the wiring harness is found to be chafed, cut, or shorted, carefully repair the damaged section using appropriate automotive wiring repair techniques (solder and heat shrink, or specialized crimp connectors) or replace the affected harness section. Ensure proper routing and protection to prevent future damage.
• Clean or Replace Corroded Connectors/Sockets: If corrosion is identified in the relay socket or connector, clean it thoroughly using electrical contact cleaner and a small brush. If corrosion is severe and has damaged the terminals, the connector or socket may need to be replaced. Apply dielectric grease to prevent future corrosion.
• Remove and Reroute Aftermarket Accessories: If improperly installed aftermarket accessories are causing the short, disconnect them. Restore the original wiring and, if the accessories are still desired, ensure they are installed with proper fusing and without interfering with critical vehicle circuits.
• Replace the Body Control Module (BCM) or General Electronic Module (GEM): If all external wiring and components test good, and the DMM still indicates a short to ground on the BCM/GEM’s output driver circuit for the relay, the BCM/GEM itself may be internally faulty. This is typically a dealer-level repair, as new modules often require programming or initialization to the vehicle.

After any repair, clear the DTC B1374 using a scan tool, and thoroughly test the illuminated entry system’s functionality. Perform a parasitic draw test again to ensure the battery drain issue has been resolved.