B1302

What Does Code B1302 Mean?

DTC B1302 indicates a circuit fault within the coil of the Accessory Delay Relay. This relay is a critical component in many vehicle electrical systems, responsible for providing power to certain convenience accessories—such as the radio, power windows, and sunroof—for a brief period after the ignition is switched off, typically until a door is opened. This feature is commonly known as “retained accessory power” (RAP).

The Body Control Module (BCM) or a similar integrated control unit (e.g., General Module, Smart Junction Box) monitors the electrical integrity of the Accessory Delay Relay’s coil circuit. This circuit typically consists of a power supply, the relay coil itself, and a ground control circuit managed by the BCM. The BCM sets code B1302 when it detects an electrical anomaly within this coil circuit. This could manifest as an open circuit (infinite resistance), a short circuit to ground, or a short circuit to battery voltage. The module actively monitors the voltage and current draw across the coil circuit when it attempts to energize or de-energize the relay. If the monitored values fall outside predefined operational parameters, indicating the coil is not drawing the expected current or is permanently powered/unpowered, the BCM registers the fault and stores B1302.

Common Symptoms

• Accessories (e.g., radio, power windows, sunroof) do not operate after the ignition is turned off, even before a door is opened.
• Intermittent or complete loss of function for the retained accessory power feature.
• The accessory delay feature operates erratically or fails to disengage properly.
• In some rare cases, persistent battery drain if the relay coil circuit is shorted in a manner that keeps the relay energized when it should not be.
• The affected accessories may not function at all, even with the ignition on, if the relay coil fault prevents the main power contacts from closing.

What Causes the Code B1302?

• Faulty Accessory Delay Relay: The internal coil of the relay may have developed an open circuit, a short circuit, or high resistance, preventing it from energizing or de-energizing correctly.
• Wiring Harness Issues:
  • An open circuit (break) in the control wire leading from the BCM/control module to the relay coil.
  • A short circuit to ground in the relay coil control wire.
  • A short circuit to battery voltage in the relay coil control wire.
  • Corrosion, damaged insulation, or loose terminals within the relay socket or associated connectors.
• Faulty Body Control Module (BCM) or Power Distribution Module (PDM): The internal driver circuit within the module responsible for supplying power or ground to the relay coil may have failed. This is less common than relay or wiring issues but remains a possibility.
• Blown Fuse: Although less common for a coil circuit specific fault, a fuse protecting the control side of the relay (if present) could be blown due to an overload or short within the coil circuit itself.

How to Diagnose and Troubleshoot

Diagnosing B1302 requires a systematic approach, often involving a digital multimeter (DMM), an OBD-II scan tool capable of accessing body control module data, and vehicle-specific wiring diagrams.

1. Initial Scan Tool Analysis: Connect an OBD-II scan tool and confirm the presence of B1302. Check for any other related diagnostic trouble codes (DTCs) in the BCM or other modules. Review freeze frame data to understand the operating conditions (e.g., ignition state, battery voltage) when the code was set.
2. Locate the Accessory Delay Relay: Consult the vehicle service manual or wiring diagram to precisely identify the location of the Accessory Delay Relay. It is commonly found in an interior fuse panel, under-dash junction box, or the underhood power distribution center.
3. Visual Inspection: Disconnect the vehicle’s battery. Visually inspect the Accessory Delay Relay, its socket, and the surrounding wiring harness for obvious signs of damage, corrosion, loose terminals, or burnt insulation. Pay close attention to the terminals that connect to the relay coil.
4. Relay Coil Resistance Test:
   • With the relay removed from its socket, identify the coil terminals (typically pins 85 and 86 on a standard Bosch-style relay).
   • Set your DMM to the ohms (Ω) scale.
   • Measure the resistance across the coil terminals. A healthy relay coil should typically show a resistance between 60 to 120 ohms. An infinite resistance (open circuit) or very low resistance (short circuit) indicates a faulty relay.
   • If possible, swap the relay with a known-good, identical relay from a non-critical circuit (e.g., horn relay) and retest the system.
5. Circuit Integrity Test (Wiring):
   • Power Side to Coil (if applicable): With the relay removed and the ignition on (or as per wiring diagram for when the coil should be powered), use the DMM set to DC voltage to test for 12V at one of the coil terminals (e.g., 85). If no voltage is present, trace the power supply circuit to identify the break or fault.
   • Control Side (Ground/Power) to Coil: Identify the wire from the BCM/control module that controls the other coil terminal (e.g., 86). With the battery disconnected and the BCM connector disconnected, use the DMM set to continuity or ohms to check for continuity between the relay socket terminal and the corresponding BCM pin. An open circuit indicates a break in the wire. Also, check for shorts to ground and shorts to voltage on this wire by touching one DMM lead to the relay socket terminal and the other to chassis ground or battery positive, respectively.
   • Voltage Drop Test: If continuity is good, perform a voltage drop test on both the power and control side wires of the coil circuit. High voltage drop indicates excessive resistance in the wiring.
6. BCM Output Verification (Advanced): If the relay and all wiring appear sound, and the code persists, the issue might lie within the BCM. Using a capable scan tool with bi-directional controls, attempt to command the Accessory Delay Relay ON and OFF while monitoring the voltage or ground signal at the relay coil control terminal with a DMM or oscilloscope. If the BCM fails to provide the correct signal when commanded, the BCM itself may be faulty.

Recommended Repairs and Solutions

The resolution for B1302 will depend directly on the diagnostic findings:

• Replace the Accessory Delay Relay: If the relay coil tested faulty (open, shorted, or incorrect resistance), replacing the relay is the most common and often simplest solution. Ensure the replacement relay matches the original specifications (part number, voltage, current rating).
• Repair or Replace Wiring Harness: If an open circuit, short to ground, or short to voltage is identified in the control wiring to the relay coil, the harness section must be repaired. Use automotive-grade wire of the correct gauge, solder connections, and protect them with heat shrink tubing. For severe damage or inaccessible sections, harness replacement may be necessary.
• Clean Corroded Connections: If corrosion is found at the relay socket or any associated connectors, thoroughly clean the terminals using an electrical contact cleaner and a small brush. Apply dielectric grease to prevent future corrosion.
• Replace Body Control Module (BCM) or Power Distribution Module (PDM): If all external wiring, fuses, and the relay itself test good, and BCM output verification confirms a fault within the module’s driver circuit, BCM replacement may be required. Be aware that BCM replacement often necessitates programming and calibration with a factory-level scan tool.
• Post-Repair Verification: After any repair, clear the DTCs with a scan tool. Cycle the ignition, operate the affected accessories to confirm normal function, and perform a brief drive cycle to ensure the code does not return. Monitor the retained accessory power feature to ensure it activates and deactivates correctly.