B1320: Driver Door Ajar Circuit Open
The B1320 code indicates that the vehicle's control module (such as the GEM in Ford or equivalent body control module) has detected an open circuit in the driver door ajar switch circuit. This switch signals whether the driver's door is open or closed by providing a variable voltage or ground signal. An open circuit means there is a break in the electrical path between the switch and the module, preventing the correct signal from reaching the system. The module interprets this lack of signal as an open circuit and stores the fault code.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty or worn driver door ajar switch
- Open or corroded wiring between the switch and control module
- Loose, corroded, or disconnected door switch connector
- Failed GEM or body control module (BCM)
- Damaged circuit board traces in the module connector
3. Symptoms You Will Notice
- Door ajar warning light stays on or flashes
- Interior dome light stays on or behaves erratically
- Power locks or alarm system may malfunction
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to the B1320 code.
Visually inspect the driver door ajar switch and its connector for damage, corrosion, or loose fit.
Test the switch operation using a multimeter: measure continuity or voltage signal with door open and closed.
Check wiring between the switch and the control module for opens, shorts, or corrosion.
If wiring and switch are good, test the control module's input circuit; replace module if faulty.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, the vehicle is generally safe to drive. However, the door ajar warning may be distracting, and interior lights may stay on, draining the battery. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Repair costs typically range from $50 to $200 for a switch replacement, up to $300-$600 if the control module needs replacement, plus diagnostic fees.