B1556 – Ignition Run/Start Circuit Open

The ODBII code B1556 indicates that there is an open circuit in the ignition run/start circuit, which means the vehicle’s ignition system is not receiving the proper signal to start or run the engine.

The severity of ODBII code B1556 is moderate to high.

Common Causes For: B1555 Ignition Run/Start Circuit Failure

• Faulty ignition switch
• Open or damaged wiring in the ignition circuit
• Poor connections or corroded terminals
• Faulty relay in the ignition system
• Malfunctioning body control module (BCM)
• Defective starter motor
• Issues with the fuse related to the ignition system

Common misdiagnosis for B1556 Ignition Run/Start Circuit Open

• Faulty ignition switch
• Bad battery connections
• Defective starter relay
• Wiring issues or shorts in the ignition circuit
• Malfunctioning body control module (BCM)
• Faulty key fob or immobilizer system
• Defective fuses related to the ignition system

Common Troubleshooting Steps

The OBD-II code B1556 indicates an issue with the ignition run/start circuit, specifically that it is open. This can lead to problems with starting the vehicle or keeping it running. Here are some common troubleshooting steps to diagnose and resolve the issue:

• Check the Vehicle’s Battery:
• Ensure the battery is fully charged and in good condition. A weak battery can cause various electrical issues.
• Inspect Fuses:
• Check the fuses related to the ignition system. A blown fuse can interrupt the circuit and cause the code to trigger.
• Examine Wiring and Connectors:
• Inspect the wiring and connectors associated with the ignition system for any signs of damage, corrosion, or loose connections. Pay special attention to the ignition switch and related harnesses.
• Test the Ignition Switch:
• The ignition switch itself may be faulty. Use a multimeter to test the switch for continuity in the run/start positions. If it fails to provide continuity, it may need to be replaced.
• Check for Ground Issues:
• Ensure that all ground connections related to the ignition system are secure and free of corrosion. Poor grounding can lead to circuit issues.
• Scan for Additional Codes:
• Use an OBD-II scanner to check for any additional trouble codes that may provide more context or indicate related issues.
• Inspect the PCM (Powertrain Control Module):
• In some cases, the PCM may be at fault. Check for any software updates or known issues with the PCM for your specific vehicle model.
• Test the Ignition Relay:
• If your vehicle uses an ignition relay, test it to ensure it is functioning properly. A faulty relay can prevent the ignition circuit from completing.
• Perform a Visual Inspection:
• Look for any signs of tampering or previous repairs that may have affected the ignition circuit.
• Consult Wiring Diagrams:
• Refer to the vehicle’s service manual for wiring diagrams to trace the ignition circuit and identify any potential breaks or shorts. 1
• Professional Diagnosis:
• If the issue persists after performing these steps, consider seeking help from a professional mechanic who can conduct more advanced diagnostics. By following these steps, you should be able to identify and resolve the issue causing the B1556 code. Always remember to take necessary safety precautions when working on a vehicle’s electrical system.