B1604: Anti-Theft Indicator Circuit Open
Diagnostic trouble code B1604 indicates that the vehicle's control module (typically the GEM, BCM, or security module) has detected an open circuit in the anti-theft system indicator light. This indicator, usually located on the instrument cluster, is activated by the security module to show the status of the anti-theft system (such as PATS on Ford vehicles). An open circuit means there is a break in the wiring between the control module and the LED or bulb, preventing it from illuminating. The PATS system may still function normally, but the driver will not receive visual feedback about the system's armed/disarmed status.
1. Commonly Affected Makes
2. Most Common Causes
- Open or broken wiring between the control module and the indicator light
- Burnt-out or damaged anti-theft indicator LED or bulb
- Corroded, loose, or disconnected indicator connector
- Internal failure of the control module (GEM/BCM) driving the indicator circuit
- Excessive resistance in the circuit due to poor splices or jumpers
3. Symptoms You Will Notice
- Anti-theft indicator light does not illuminate when the system is armed or disarmed
- No visual feedback for the anti-theft system status
4. Step-by-Step Diagnosis
Visually inspect the anti-theft indicator light for damage or burnout
Check wiring and connectors between the control module and indicator for breaks, corrosion, or looseness
Test for voltage and ground at the indicator connector with the system active
If wiring and indicator are good, suspect a faulty control module (GEM/BCM)
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive. The anti-theft system may still function, but you will not have visual confirmation of its status. The severity is low.
How much does it cost to fix?▼
Repair costs typically range from $50 to $200, depending on whether it's a simple bulb replacement, wiring repair, or module replacement.