B1351 — Ignition Key-In Circuit Short To Battery #

Note: The code description may vary depending on the vehicle manufacturer (OEM). Always consult your specific service manual for exact terminology.

• Ignition Key-In Circuit Short to Battery (Ford, Lincoln, Mercury)
• Ignition Key Warning Circuit Short to Battery (Mazda)
• Key-In Detect Circuit Shorted to B+ (General Motors)

Summary of DTC B1351 #

The B1351 diagnostic trouble code (DTC) indicates that the ignition key-in circuit—the electrical path that monitors whether the key is in the ignition—has a short to battery voltage (B+). In practical terms, this means the circuit is registering power when it shouldn’t, typically due to a wiring issue or component fault. This code is set by the body control module (BCM) or similar control unit when it detects abnormal voltage in the key-in detection system. While this code does not usually affect engine performance, it can disrupt warning chimes, security features, or accessory power functions. Early diagnosis can prevent lockout scenarios and ensure proper warning signals.

Frequent Symptoms for DTC B1351 #

Drivers and technicians may notice various signs when code B1351 is present. These symptoms often relate to the vehicle’s warning and security systems rather than driveability:

• Key-in ignition warning chime sounds at the wrong times or not at all
• Interior lights stay on or fail to turn on/off properly
• Door ajar or key reminder warning light illuminated
• Accessory power (e.g., radio) remains on or cuts off unexpectedly
• Security/anti-theft system may not arm or disarm properly
• Occasional battery drain due to circuits remaining active

Probable Causes for DTC B1351 (in order of likelihood) #

The most common causes of a B1351 code involve issues within the key-in detection circuit. Here’s what typically goes wrong, starting with the most likely:

1. Damaged or shorted wiring in the key-in detection circuit
2. Faulty ignition switch (the mechanism sensing key insertion)
3. Corroded or loose connector at the ignition cylinder or BCM
4. Body control module (BCM) malfunction
5. Aftermarket accessories improperly spliced into ignition wiring

Step-by-Step Diagnostic for DTC B1351 #

Diagnosing B1351 requires a systematic approach to isolate the fault. Here’s how a technician should proceed:

• Verify the code with a professional OBD-II/EOBD scan tool and note any related codes.
• Consult the vehicle’s wiring diagram for the key-in circuit.
• Visually inspect the ignition switch and surrounding wiring for signs of damage or aftermarket modifications.
• Check connectors at the ignition cylinder and BCM for corrosion, bent pins, or poor fit.
• With the key out, use a multimeter to check for unexpected battery voltage at the key-in signal wire; trace and repair any shorts to power.
• Test the ignition switch’s key detection function using the OEM procedure.
• If wiring and switch are good, use scan tool data and bi-directional tests (if available) to check BCM response to key-in status.
• Clear the code and retest after each repair step to confirm resolution.

Possible Repairs for DTC B1351 #

The repair will depend on the identified root cause. Common solutions include:

• Repair or replace damaged wiring or connections in the key-in circuit
• Replace a faulty ignition switch or key-in detection sensor
• Clean and secure connectors at the ignition cylinder and BCM
• Remove or properly integrate any aftermarket accessories interfering with the circuit
• In rare cases, replace or reprogram the BCM if internal fault is confirmed

Is It Safe to Drive with Code B1351? #

Yes, but with limitations: Code B1351 typically does not impact the vehicle’s drivability or safety directly. However, it may cause loss of warning chimes, improper operation of interior lights, or security system malfunctions. If you rely on these features (e.g., key reminder to prevent lockouts, or anti-theft functions), address the issue promptly. Prolonged neglect can also risk battery drain.

Vehicles Most Commonly Affected by DTC B1351 #

While B1351 is seen across several brands, it is most commonly reported in the following vehicles:

• Ford F-Series (F-150, F-250, etc.)
• Ford Explorer, Taurus, Focus
• Lincoln Town Car, Navigator
• Mazda Tribute (Ford-based platform)
• Mercury Grand Marquis, Mountaineer
• Some General Motors trucks and SUVs

Common Mistakes & Best Practices for DTC B1351 #

Technicians and DIYers sometimes overlook key details when tackling this code. Avoid these errors:

• Skipping the wiring inspection and replacing the ignition switch prematurely
• Ignoring aftermarket alarm or remote start system interference
• Failing to check connectors for corrosion or loose pins
• Not clearing the code after repairs to confirm the fix
• Overlooking BCM software updates or TSBs (Technical Service Bulletins) that may address false codes

Quick FAQ for DTC B1351 #

Q: Will B1351 cause my car not to start?
A: Generally, no. This code affects the key-in detection circuit, not the starter or immobilizer—unless the BCM disables starting as a theft-prevention measure, which is uncommon.

Q: Can I reset the code by disconnecting the battery?
A: You may temporarily clear the code, but if the underlying issue remains, B1351 will return. Permanent repair requires addressing the root cause in wiring, switch, or module.