B1304 Accessory Delay Relay Coil Circuit Short To Battery

Introduction:

The B1304 Diagnostic Trouble Code (DTC) indicates a fault within the accessory delay relay circuit, specifically a short to battery on the coil side. This means the relay coil, responsible for energizing the relay and allowing power to flow to accessory circuits, is receiving unintended direct voltage from the battery. This can lead to accessories remaining powered on even when the ignition is off, draining the battery and potentially damaging electrical components. Understanding the causes, symptoms, and diagnostic procedures associated with B1304 is crucial for effective troubleshooting and repair.

Table: B1304 Accessory Delay Relay Coil Circuit Short To Battery

Topic	Description	Potential Consequences
Definition of B1304	A diagnostic trouble code (DTC) indicating a short to battery in the accessory delay relay coil circuit. This means the relay's coil, which should only receive power when the ignition is on (or in accessory mode), is receiving constant voltage directly from the battery.	Battery drain, accessory malfunction, potential damage to electrical components, fire hazard (in extreme cases).
Accessory Delay Relay Function	The accessory delay relay controls power to various vehicle accessories (e.g., radio, power windows, sunroof) after the ignition is switched off. It allows these accessories to function for a short period (typically 10-30 minutes) or until a door is opened, providing convenience for the driver and passengers. This relay is typically controlled by the Body Control Module (BCM).	Accessory malfunctions, accessories staying on longer than intended, or not turning on at all after the ignition is switched off.
Common Causes	- Damaged Wiring: Worn, chafed, or cut wiring insulation allowing the relay coil circuit wire to contact a positive voltage source (typically battery voltage). This is often found near harnesses that flex or are exposed to heat and vibration. - Faulty Relay: Internal short circuit within the accessory delay relay itself, causing the coil to be permanently energized. - BCM Malfunction: Less commonly, a malfunctioning Body Control Module (BCM) could send a constant voltage signal to the relay coil, mimicking a short to battery. This is rare, but should be considered after eliminating wiring and relay issues. - Improper Wiring Modifications: Aftermarket accessory installations or repairs that were not properly executed, leading to wires being inadvertently connected to the wrong circuits.	Battery drain, accessory malfunction, potential damage to electrical components, fire hazard (in extreme cases).
Symptoms	- Battery Drain: The most common symptom; the vehicle's battery discharges rapidly, especially overnight. - Accessories Remain On: Accessories controlled by the relay (radio, power windows, etc.) continue to function even after the ignition is turned off and the key is removed. - Relay Clicking or Humming: The relay may continuously click or hum, indicating it's constantly being energized and de-energized. - Difficulty Starting: If the battery is significantly drained, the vehicle may be difficult or impossible to start. - No start condition: If the accessory delay relay controls critical engine functions, a short to battery could keep the relay permanently energized, preventing the engine from starting.	Battery drain, accessory malfunction, potential damage to electrical components, fire hazard (in extreme cases), no start condition.
Diagnostic Steps
Tools Needed	- Multimeter (capable of measuring DC voltage and resistance/continuity) - Wiring diagram for the specific vehicle model and year. - Basic hand tools (screwdrivers, pliers, wire strippers/crimpers) - Wire connectors (butt connectors, crimp connectors) - Electrical tape or heat shrink tubing - Circuit tester (optional, but helpful)	Accurate diagnosis and repair.

Detailed Explanations:

Definition of B1304:

The B1304 DTC is a standardized OBD-II (On-Board Diagnostics II) code that indicates a specific electrical fault within the vehicle's system. In this case, it means the circuit controlling the accessory delay relay coil has a short to battery. The Electronic Control Unit (ECU) or Body Control Module (BCM) detects this unexpected voltage on the relay coil circuit and sets the B1304 code. The relay coil is meant to be energized only when the ignition is on or in accessory mode, so any constant voltage on the circuit signals an issue.

Accessory Delay Relay Function:

The accessory delay relay provides power to convenience features like the radio, power windows, sunroof, and sometimes interior lighting, for a short period after the ignition is turned off. This is a convenience feature that allows occupants to finish a phone call, roll up the windows, or listen to the radio without leaving the ignition on and draining the battery. The relay is typically controlled by the Body Control Module (BCM), which monitors door switches and a timer to determine when to cut power to the accessories.

Common Causes:

Damaged Wiring: This is the most frequent culprit. Over time, wiring insulation can become brittle and crack, exposing the bare wires. If the exposed wire touches a source of battery voltage (another wire, a metal component connected to the battery), it creates a short to battery. Look for chafing, cuts, or corrosion in wiring harnesses, especially where they pass through tight spaces or are subjected to movement.
Faulty Relay: Internal failures within the relay can cause a short circuit. The coil winding inside the relay may break down, allowing current to flow directly from the battery source to the relay's output, bypassing the intended control circuit.
BCM Malfunction: Although less common, a malfunctioning BCM can send a constant voltage signal to the accessory delay relay coil, even when it shouldn't. This could be due to internal component failure within the BCM.
Improper Wiring Modifications: If aftermarket accessories have been installed or repairs have been made to the vehicle's electrical system, improper wiring connections can lead to a short to battery. Ensure all modifications are done correctly and according to established standards.

Symptoms:

Battery Drain: This is the most noticeable symptom. The constant voltage on the relay coil causes the accessories to remain powered on (or partially powered on) even with the ignition off, draining the battery overnight or over a few days.
Accessories Remain On: The accessories controlled by the relay (radio, power windows, etc.) will continue to function even after the ignition is switched off and the key is removed. This is a clear indication of a problem with the accessory delay circuit.
Relay Clicking or Humming: A relay that's rapidly cycling on and off due to a fluctuating voltage signal can produce a clicking or humming sound. This is often a sign of a short circuit or intermittent connection.
Difficulty Starting: If the battery is significantly drained by the parasitic draw caused by the short to battery, the vehicle may be difficult or impossible to start.
No start condition: If the accessory delay relay controls critical engine functions or provides power to the PCM, a short to battery could keep the relay permanently energized, preventing the engine from starting.

Diagnostic Steps:

Visual Inspection: Begin by carefully inspecting the wiring harness and connectors associated with the accessory delay relay. Look for signs of damage, such as chafing, cuts, corrosion, or melted insulation. Pay close attention to areas where the harness is routed near sharp edges, moving parts, or heat sources.
Relay Testing: Test the accessory delay relay using a multimeter. Check for continuity between the coil terminals with the relay de-energized. Also check for continuity between the coil terminals and the relay case (ground). Replace the relay if it fails any of these tests. A good relay should have high resistance (open circuit) between the coil terminals and the case.
Circuit Testing: With the relay removed, use a multimeter to check for voltage at the relay coil terminals in the wiring harness. One terminal should have battery voltage with the ignition on (or in accessory), and the other should be ground. If battery voltage is present on both terminals with the ignition off, there's a short to battery in the wiring.
Wiring Diagram Review: Consult a vehicle-specific wiring diagram to identify the exact wiring path of the accessory delay relay circuit. This will help you trace the circuit and locate the short. Wiring diagrams are essential for understanding the circuit layout and identifying potential problem areas.
BCM Testing: As a last resort, if wiring and relay are confirmed to be good, suspect a BCM issue. This will likely require specialized diagnostic tools and a qualified technician. BCM testing often involves using a scan tool to monitor BCM inputs and outputs and verify proper operation.
Component Isolation: Disconnect components one by one that are powered by the accessory delay relay to see if the short disappears. This helps isolate which part of the circuit is causing the issue. For example, disconnect the radio, then the power window module, etc., and recheck for the B1304 code after each disconnection.

Frequently Asked Questions:

What does the B1304 code mean? It indicates a short to battery in the accessory delay relay coil circuit, causing the relay to be energized when it shouldn't be.
Can I drive my car with a B1304 code? While you can drive, it's not recommended due to the risk of battery drain and potential damage to electrical components.
How do I find the accessory delay relay? Consult your vehicle's repair manual or wiring diagram for the exact location of the relay, as it varies between makes and models.
Is it possible to fix this myself? If you are comfortable with electrical troubleshooting and have the necessary tools, you may be able to diagnose and repair the issue yourself. However, if you are not experienced, it is best to consult a qualified technician.
How much will it cost to fix a B1304 code? The cost can vary widely depending on the cause of the short, the complexity of the repair, and the labor rates of the repair shop.

Conclusion:

The B1304 code signifies a potentially serious electrical issue that can lead to battery drain and accessory malfunction. Thorough diagnosis and repair are crucial to prevent further damage and ensure the vehicle's reliable operation.