Summary
B1600 is a Ford-specific code indicating the Passive Anti-Theft System (PATS) received a transponder key code that does not match any of the keys programmed into the vehicle's PATS module. The most common cause is a faulty key transponder (35%), followed by an issue with the PATS transceiver (antenna ring) around the ignition cylinder (25%) and a need for key reprogramming (20%). When this code is active, the theft indicator light typically flashes rapidly and the engine will either not start or will start and immediately stall.
Severity: High — vehicle may not start or may start then immediately stall
Safe to drive: Yes, if the engine is running — the issue is starting the vehicle, not driving it
Repair cost: $50–$500 depending on cause
DIY difficulty: Moderate to Hard
What does B1600 mean?
Ford's Passive Anti-Theft System (PATS), also called SecuriLock, uses a transponder chip embedded in the key head. When you insert the key and turn the ignition, a small antenna ring (transceiver) around the ignition lock cylinder sends an RF signal that powers the transponder chip. The chip responds with its unique code, which the PATS module compares against its list of programmed key codes. If the code matches, the PATS module authorizes the PCM to allow fuel injection and engine starting.
B1600 is set when the PATS module successfully reads a transponder code from the key, but the code does not match any of the codes stored in its memory. This is different from a "no key detected" fault — the system is reading a code, but it's the wrong one. The PATS module then instructs the PCM to disable fuel injectors, and the engine either won't start or starts on the initial crank but dies within 1–2 seconds.
The PATS system has been used in Ford, Lincoln, and Mercury vehicles since the late 1990s. Each vehicle can typically have up to 8 keys programmed. If a key's transponder is damaged, a non-PATS key is used, or the PATS module's memory has been corrupted, B1600 will result.