Ford PATS Codes and No-Start Problems

What the passive anti-theft system does

PATS stands for Passive Anti-Theft System. The key carries a small transponder chip in its head and no battery of its own. A transceiver ring around the ignition cylinder throws out a low-frequency field that powers the chip, and the chip answers with its stored code. The PATS control module compares that code against the keys already programmed to the vehicle. When it matches, the module tells the powertrain control module to enable the fuel pump, the injectors, and the starter. When it does not match, the engine can crank and die within a second or two, or refuse to crank, and the theft light comes on or flashes.

PATS is a separate system from remote keyless entry. A fob that will not lock the doors and a no-start that lights the theft indicator are usually two different faults. Treat a door lock complaint and a start complaint as separate jobs.

The PATS and security codes in this catalog

The catalog carries the Ford PATS codes that show up when the system refuses a key. B1600 means the transceiver did not receive a signal from the ignition key transponder at all, which points at a non-PATS key, a failed chip, or aftermarket remote start interference. B1601 means the module read a key code but did not recognize it, which points at an unprogrammed or wrong key. B1681 means the module lost the signal from the transceiver itself, so look at the module, its fuse, and its wiring. B2103 means the antenna is not connected, common after steering column work. P1260 is the immobilizer code: the vehicle was immobilized because the theft logic did not pass.

Two more codes get mistaken for PATS troubles. B10AB is a remote keyless entry fob that fell out of sync, which affects locking and unlocking, not starting. B2100 is a worn driver door key cylinder switch, a door lock input rather than an immobilizer fault.

Why a security no-start is usually the key or the ring

On a Ford that cranks and dies with the theft light on, the part that fails least is the control module. The key chip and the antenna ring fail far more often. A key that turns the ignition perfectly can still have a dead or damaged transponder, because the blade and the chip are separate things. Testing is cheap. Try a second working key on its own with no other transponder keys on the ring. If the second key starts the engine, the first key is the suspect.

Interference is real. Other PATS keys, foil stickers, brass key tags, and a gas station or loyalty transponder dangling on the same ring can block the read. Move them off the ring and retry. Also know what reprogramming cannot do. Erasing and reprogramming keys does not cure an intermittent PATS no-start. If no fault can be found, do not reprogram as a guess, and reprogramming the PCM does not change PATS behaviour either.

Check order before you replace anything

1. Second key, alone. Use a known-good Ford PATS key with nothing else on the ring. This splits a key fault from a vehicle fault in one step.
2. Watch the theft light. At key on, a normal system lights it for about three seconds and then puts it out. A light that keeps flashing or stays lit marks a PATS fault.
3. Antenna ring and connector. Check that the transceiver ring is seated around the ignition cylinder and that its connector is fully home and free of corrosion. Column work is a common cause of a loose ring.
4. Power and fuses. Check the PATS fuses and the module power and ground before condemning the module.
5. Scan for codes. Pull the PATS and body codes. B1600, B1601, B1681, and B2103 each point at a different part of the chain.

Work this list top to bottom. Skipping the second-key test is how people end up buying a module they did not need.

When the problem is the lock, not the chip

Not every no-start is a security refusal. A worn ignition lock cylinder, a bent key, or a broken actuator can stop the key from turning at all, which is a mechanical repair, not a programming job. On the door side, B2100 covers a failed driver door key cylinder switch. Low battery voltage also causes strange start behaviour and can corrupt a start attempt, so charge the battery fully before chasing the security system. These faults show different symptoms: a lock that will not turn, versus a lock that turns and the engine still dies. Match the symptom to the system before you test anything.

When to stop and call a locksmith or dealer

Key programming is where DIY stops. Ford changed the rules over the years. The early systems allowed a self-program with two working keys in a timed ignition sequence. Later generations require a Ford-capable programmer and security access, and an all-keys-lost job always needs that security access procedure. That is equipment and authority a home garage does not have.

A professional locksmith with Ford-capable tools performs the same programming as a dealer, so you are not locked into the dealership. What you should not do is buy a used module and expect to bolt it in. When the PATS module is separate from the PCM it usually has to be programmed to the vehicle, and it is not a normal parts-store item. The transceiver ring, on the other hand, is a modest part and a common fix once the codes and tests point at it.