B1303

What Does Code B1303 Mean?

The diagnostic trouble code B1303 indicates an “Accessory Delay Relay Coil Circuit Open”. This code specifically points to an electrical integrity issue within the control circuit for the Accessory Delay Relay (ADR). The ADR is a critical component of the vehicle’s Retained Accessory Power (RAP) system, which provides power to certain accessories (such as the radio, power windows, and sunroof) for a brief period after the ignition is turned off, typically until a door is opened. The Body Control Module (BCM) or a similar integrated control unit (e.g., Generic Electronic Module – GEM) is responsible for monitoring and commanding this relay. When the BCM attempts to energize the ADR coil, it supplies voltage to one side of the coil and typically provides a switched ground path on the other. If the BCM detects an abnormally high resistance or a complete interruption (open circuit) in this coil control circuit, meaning it cannot establish a proper current flow to activate the relay, it registers the B1303 code. This prevents the relay from closing its contacts, thereby disabling the RAP function and potentially other accessories if the relay supplies them directly.

Common Symptoms

• Loss of Retained Accessory Power (RAP) Function: The most direct symptom is that accessories like the radio, power windows, or sunroof will immediately lose power when the ignition is turned off, instead of remaining active until a door is opened.
• Specific Accessories Inoperative: Depending on the vehicle’s electrical architecture, if the ADR directly controls the main power feed for certain accessories, those accessories might be completely inoperative even with the ignition in the ON position.
• No Audible Click from Relay: When attempting to operate accessories that rely on the ADR, there will be no audible click indicating the relay is actuating.
• Warning Lights: While a B-code typically does not trigger the Malfunction Indicator Lamp (MIL – Check Engine Light), other dashboard warning lights related to electrical system faults or comfort/convenience features might illuminate.

What Causes the Code B1303?

• Faulty Accessory Delay Relay: The most common cause is an internal failure of the relay itself, where the electromagnetic coil within the relay develops an open circuit or high resistance, preventing it from being energized.
• Open Circuit in Wiring Harness: A break, significant corrosion, or high resistance in the wiring connected to the ADR coil circuit. This could affect either the power feed to the coil or the ground-side control wire from the BCM.
• Poor Electrical Connections: Corroded, loose, or damaged terminals at the relay socket, or at the connector for the Body Control Module (BCM) or other controlling module.
• Faulty Body Control Module (BCM) / Generic Electronic Module (GEM): Less frequently, the driver circuit within the BCM responsible for supplying the ground or power to energize the relay coil could be defective.

How to Diagnose and Troubleshoot

Diagnosis of B1303 requires a systematic approach, utilizing a digital multimeter (DMM) and relevant wiring diagrams.

1. Verify the Complaint: Confirm the RAP function is indeed inoperative. Turn the ignition to the ON position, then OFF, but do not open any doors. Check if the radio or power windows operate.
2. Retrieve Diagnostic Data: Use an OBD-II scanner to confirm B1303 is present. Check for any associated freeze-frame data, although B-codes may have limited freeze-frame information.
3. Locate the Accessory Delay Relay: Consult the vehicle’s service manual or wiring diagram to precisely locate the ADR. It is typically found in an under-dash fuse box, an under-hood power distribution center, or integrated into a module.
4. Visual Inspection: Disconnect the battery. Visually inspect the ADR, its socket, and the surrounding wiring for signs of damage, corrosion, melted plastic, or loose connections. Pay close attention to the terminals within the relay socket.
5. Test Relay Coil Power and Ground (at Socket):
   • With the relay removed, use the wiring diagram to identify the two terminals in the relay socket corresponding to the coil circuit.
   • Reconnect the battery. Turn the ignition to the ON position (or simulate the condition for RAP activation as per service manual).
   • Using a DMM, measure the voltage between the coil power feed terminal and a known good chassis ground. You should read battery voltage. If not, troubleshoot the power supply circuit (fuse, wiring).
   • Next, measure the voltage between the coil control terminal (typically switched ground from the BCM) and a known good battery positive terminal. When the BCM commands the relay ON, you should observe near battery voltage, indicating the BCM is completing the ground circuit. If no voltage change is observed when commanded, the BCM output or the wiring to it is suspect.
6. Test the Accessory Delay Relay Itself:
   • Remove the ADR. Using a DMM, measure the resistance across the two coil terminals of the relay. A good relay coil should exhibit a relatively low resistance value (e.g., 50-200 ohms, specifications vary). An “open” coil will show an infinite resistance (OL on most DMMs), confirming a faulty relay.
   • As an alternative test, carefully apply fused battery voltage and ground directly to the relay coil terminals (observing polarity if applicable). You should hear an audible click as the relay actuates. If no click is heard, the relay is faulty.
7. Perform Continuity and Resistance Checks on Wiring: If the relay tests good and power/ground were intermittent or absent at the socket, perform continuity and resistance checks on the wiring between the relay socket and the BCM (or controlling module) using the wiring diagram. Look for an open circuit or excessively high resistance in both the power and control wires leading to the relay coil.
8. BCM Output Test (Advanced): If all wiring and the relay test good, and the BCM is not providing the correct control signal, perform a bi-directional control test using an advanced diagnostic scanner to command the relay ON/OFF. If the command fails to actuate the relay and all external circuits are verified, this points to an internal BCM fault.

Recommended Repairs and Solutions

Once the root cause of B1303 has been precisely identified, the appropriate repairs can be made:

• Replace the Accessory Delay Relay: If diagnostic testing confirms an open circuit within the relay coil, replacing the ADR is the most common and direct solution. Always use a high-quality OEM equivalent or a reputable aftermarket relay to ensure proper function and longevity.
• Repair or Replace Damaged Wiring: If an open circuit, high resistance, or severe corrosion is found in the wiring harness connected to the ADR coil, repair the damaged section using proper automotive wiring repair techniques (soldering, heat shrink, appropriate gauge wire). For extensive damage, replacement of the relevant harness section may be necessary.
• Clean or Replace Corroded Connectors: If corrosion or damage is found at the relay socket terminals or the BCM connector, thoroughly clean the affected terminals using electrical contact cleaner and a suitable brush. If terminals are severely corroded or bent, replace the individual pins or the entire connector assembly.
• Replace the Body Control Module (BCM) / Generic Electronic Module (GEM): If all other components (relay, wiring, connectors) have been thoroughly tested and verified to be in good working order, and diagnostic procedures unequivocally point to an internal failure of the BCM’s relay driver circuit, the BCM will require replacement. This often involves additional costs for module programming and calibration specific to the vehicle, and should only be undertaken after exhausting all other diagnostic possibilities.

After any repair, clear the DTCs using an OBD-II scanner and perform a functional test of the Retained Accessory Power system to confirm the issue has been resolved.