B1351

What Does Code B1351 Mean?

DTC B1351, or “Ignition Key-In Circuit Short To Battery,” indicates that the vehicle’s Body Control Module (BCM), or a similar integrated control unit responsible for monitoring ignition system states, has detected an anomalous voltage condition on the ignition key-in sense circuit. Specifically, the BCM registers a voltage on this circuit that is consistent with battery voltage (B+) when the ignition key is either removed from the cylinder or when the system logic dictates that no key should be detected. This implies that the key-in switch is stuck in a closed or “key detected” position, or the wiring supplying its signal to the BCM is shorted to a constant power source. This subsystem is critical for functions such as accessory power management, anti-theft systems, and driver convenience features like warning chimes.

Common Symptoms

• Constant “Key In Ignition” Warning: The instrument cluster may display a warning message or illuminate a warning light indicating the key is in the ignition, even when it has been removed.
• Persistent Accessory Power: Vehicle accessories (e.g., radio, power windows) may remain active after the key is removed and the door is opened, leading to parasitic battery drain.
• No Ignition Key-In Chime: The audible chime typically associated with leaving the key in the ignition with the door open may not sound or may sound continuously.
• Remote Start/Immobilizer Issues: Malfunctions with remote start systems or the vehicle’s immobilizer, potentially preventing the engine from starting or cranking.
• Battery Drain: A consistent short to battery on this circuit can prevent various modules from entering sleep mode, leading to a discharged battery over time.

What Causes the Code B1351?

• Faulty Ignition Key-In Switch: The most common cause is an internal malfunction of the key-in switch located within the ignition cylinder. The switch may be stuck in the “closed” position, or its internal contacts may be shorted to a power supply.
• Wiring Harness Short to Battery: The wiring leading from the ignition key-in switch to the BCM may have chafed insulation, causing it to short directly to a constant B+ voltage source within the wiring harness. This often occurs near the steering column or firewall pass-throughs.
• Corroded or Damaged Connectors: Electrical connectors at the ignition switch or the BCM can accumulate corrosion or sustain damage, leading to unintended bridges between terminals and creating a short to battery voltage.
• Internal Body Control Module (BCM) Fault: Less frequently, an internal short or failure within the BCM itself could cause it to falsely interpret the key-in circuit status or exhibit an internal short to B+.
• Aftermarket Accessory Interference: Improperly installed aftermarket alarm systems, remote starters, or audio equipment can sometimes be incorrectly wired into the key-in circuit, causing a short to battery.

How to Diagnose and Troubleshoot

Diagnosis of B1351 requires a methodical approach, utilizing a digital multimeter (DMM) and a vehicle-specific wiring diagram.

1. Verify the Code and Check for Related DTCs: Use an OBD-II scanner to confirm B1351 is active or stored. Check for any other related Body (B-codes) or Network (U-codes) diagnostic trouble codes that might provide additional context, such as BCM communication errors.
2. Visual Inspection:
   • Disconnect the vehicle’s battery for safety.
   • Carefully inspect the ignition key cylinder area for any signs of physical damage, loose components, or foreign objects that might be jamming the key-in switch.
   • Trace the wiring harness from the ignition switch down the steering column and towards the BCM. Look for any signs of chafing, pinching, or heat damage to the wire insulation.
   • Inspect the electrical connectors at both the ignition switch and the BCM for corrosion, bent pins, or loose terminals.
3. Isolate and Test the Key-In Switch Circuit (Using DMM):
   • Obtain the vehicle’s specific wiring diagram to identify the exact wire for the key-in circuit between the ignition switch and the BCM. Note the expected voltage states (e.g., 0V key out, B+ key in, or vice-versa depending on design).
   • At the Ignition Switch: With the battery reconnected (or external power source), key removed, and ignition off, backprobe the key-in circuit wire at the ignition switch connector. A DMM should read approximately 0V (or ground potential) if the key is out and the switch is functioning correctly. If you measure battery voltage, the ignition key-in switch itself is likely internally shorted.
   • Continuity and Short-to-Power Test (Wiring Harness): Disconnect the battery again. Disconnect both the ignition switch connector and the BCM connector. Isolate the key-in circuit wire.
     • Measure the resistance between this wire and vehicle chassis ground. There should be no continuity (infinite resistance) if the circuit is isolated.
     • Measure the resistance between this wire and any known B+ power wires in the same harness. There should be no continuity (infinite resistance). If a low resistance is measured, a short to power exists in the wiring harness.
   • BCM Input Verification: If the wiring and switch appear to be functioning correctly, but the code persists, reconnect all components except the key-in switch (if possible to isolate). With the key removed and ignition off, measure the voltage on the BCM input pin for the key-in circuit. If battery voltage is still present, the BCM itself may be faulty.
4. Check Aftermarket Accessories: If present, temporarily disconnect any aftermarket alarm systems, remote starters, or stereo equipment that may have been wired into the ignition system to rule out interference.

Recommended Repairs and Solutions

Once the root cause of B1351 has been identified through accurate diagnosis, implement the following repairs:

• Replace Faulty Ignition Key-In Switch: If the diagnostic steps confirm an internal short or malfunction within the ignition key-in switch, replace the switch mechanism. In some vehicles, this may require replacing the entire ignition cylinder assembly. Always use OEM or high-quality aftermarket components.
• Repair or Replace Damaged Wiring Harness: If a short to battery voltage is found within the wiring harness, the damaged section must be repaired. Carefully splice in new wire of the correct gauge, using solder and heat-shrink tubing for robust, insulated connections. If the damage is extensive, consider replacing the entire affected section of the harness. Ensure the repaired wire is properly routed and secured to prevent future chafing.
• Clean or Replace Corroded Connectors: For corroded electrical connectors, use a specialized electrical contact cleaner and a small brush to remove all corrosion. Inspect terminals for damage and repair or replace any bent or broken pins. If corrosion is severe and has compromised the connector integrity, replace the connector shell and/or individual terminals.
• Replace Body Control Module (BCM): If all other components (key-in switch, wiring harness, connectors) are meticulously verified as functional, and the BCM is confirmed to be misinterpreting the signal or has an internal fault, the BCM will require replacement. Be aware that BCM replacement often necessitates programming and synchronization with the vehicle’s immobilizer system, which typically requires a dealership-level scan tool or specialized programming equipment.
• Correct Aftermarket Wiring: If aftermarket accessories were found to be interfering, properly re-wire them according to manufacturer specifications or remove them if they are the direct cause of the short.
• Clear DTCs and Verify Repair: After any repair, clear the B1351 code using an OBD-II scanner. Perform several ignition cycles (key in/out, start/stop, door open/close) and test all related accessory functions to ensure the code does not return and the system operates as intended. Monitor live data for the key-in circuit status if available on the scan tool.