OBD2 Code B1556: Ignition Run/Start Circuit Open
The B1556 code indicates that the control module has detected an open circuit in the ignition Run/Start signal. This circuit supplies power or a status signal to the module when the ignition key is in the RUN or START position. In Ford vehicles, this code typically occurs when the Body Control Module (BCM) or Smart Junction Box (SJB) does not receive the expected signal from the ignition circuit, preventing the engine from starting or causing failures in auxiliary systems that rely on this signal to activate.
1. Commonly Affected Makes
2. Most Common Causes
- Blown or corroded ignition fuse
- Faulty ignition relay
- Open or damaged wiring between the ignition switch and control module
- Corroded or loose ignition switch connector
- Defective ignition switch
- Internal failure of the BCM or SJB
- Poor ground in the ignition circuit
3. Symptoms You Will Notice
- Engine cranks but does not start
- No crank condition
- Dashboard lights or accessories not working in RUN position
- Stalling or intermittent electrical issues
4. Step-by-Step Diagnosis
Check ignition fuses and relays for continuity and corrosion
Inspect wiring and connectors between ignition switch and BCM/SJB for damage or looseness
Test ignition switch output voltage in RUN and START positions
Verify ground connections in the ignition circuit
If all else passes, test or replace the BCM/SJB
5. Frequently Asked Questions
Is it safe to drive?▼
No, this code indicates a high-severity issue that can prevent the vehicle from starting or cause sudden electrical failures while driving. It is not safe to drive until the problem is diagnosed and repaired.
How much does it cost to fix?▼
The cost varies depending on the cause. A blown fuse or relay can cost under $50, while replacing an ignition switch ranges from $150 to $300. If the BCM or SJB needs replacement, expect $500 to $1,200 including labor.