Ford PATS

By Glen Beanard technical contributor

P.A.T.S. stands for passive anti-theft system. It is called passive because it requires no action on the part of the driver. Ford likes to play an annoying little game of PATS hide-and-go-seek. That is to say, they cant seem to decide where they want to put the PATS system. Not only do they play hide and seek with it, they keep changing how it operates. There are five different PATS systems, you will need to review technical information specific to the vehicle you are servicing prior to beginning any diagnostic work on a PATS system.

The Key

The PATS system uses a key that contains a tiny electronic device called a transponder located inside the handle. The transponder emits a radio frequency code that is read by the PCM or PATS module (system type dependent).

The key is electronic, but requires no batteries. It is powered by a radio frequency field surrounding the opening of the ignition key cylinder. This RF field is created by the transceiver that is located at the open end of the cylinder just beneath the column shrouding. The RF frequencies are picked up by a tiny coil located in the transponder that serves as an antenna. The coil then transfers that energy into a tiny capacitor as an electrical charge. The newly charged capacitor serves as a battery to temporarily power the transponders logic circuitry. Once powered up, the logic circuitry then returns its coded message back through the coil. The coil once again serves as an antenna, but only this time it is sending instead of receiving. The coil emits its coded message out of the head of the key via radio waves to be picked up by the transceiver.

The transceiver

The duties of the transceiver are to supply power to the transponder in the key head, receive the transponders coded message, and then to send that encoded message to the PATS module or PCM via hard wiring. The transceiver may communicate with the key twice, depending on the system type. The first reading comes as soon as the key-in sense switch has been tripped. The second comes when the cylinder is switched to the on position. For systems where the PCM performs all of the PATS functions, there will only be one code reading. That reading will take place at the key-on position as soon as the PCM wakes up. On a system that contains the PATS module in the cluster, the cluster will have woken as soon as the door handle was lifted to enter the vehicle. The cluster will be ready to receive the code reading long before the key-in sense switch is tripped by the driver.

The transceiver module is a slave to the PATS module. The transceiver makes no decisions. Even when to read the key code is a decision that is not in the hands of the transceiver.

The transceiver is located at the open end of the cylinder just beneath the column shrouding. It is secured by one screw, usually a T-20 non-security style torx. The body of the transceiver is square with a loop that extends from the side of it to surround the opening of the ignition key cylinder. (see transceiver 1 photo)

The PATS Module

The PATS module can be a standalone module, it can be integrated into the instrument cluster, or all functions of the PATS can be contained inside the PCM, depending on year and model.

The duties of the PATS module are to:

1.     Initiate the key read.

2.     Store the key codes in non-volatile memory.

3.     Compare the users key code against the stored key codes

4.     Sending ok to start and do not start messages to the PCM via the SCP network or hardwiring depending on year and model.

5.     Perform diagnostic checks.

6.     Control the theft indicator light.

The Warning Light

The PATS warning light may be a red light on the cluster that says Theft, or a red L.E.D. light on the top of the dash anywhere between the left side of the dash to the center. The warning light serves as both, a visual deterrent to thieves and information feedback to the driver or technician.

The theft light will flash in two second intervals when the key is off. This is only a visual deterrent on vehicles with PATS only. The light will flash rapidly or stay on steady in the event that an incorrect key code, or no code at all, is received by the PATS module or PCM.

For normal operation on a good working PATS system that has received a valid key code matching one of the stored codes, the theft light will come on and then turn off after 3 seconds. That is called prove out. The bulb prove out feature is also needed to observe during key programming and it very important to observe when diagnosing a no start condition on a PATS equipped vehicle.

PCM

Depending on the exact PATS system being used, the PCM may assume all of the duties of the PATS module. At the very least, the PCM is what disables the engine in the event that a theft has been detected.

Over the years, the PCMs strategies have changed in this regards. On the older systems, the PCM would only deny the fuel pump and injectors in the event of a theft. On these older systems, the starter would still engage and the ignition system would still fire. If a technician were to spray carburetor cleaner or propane into the intake manifold, the engine would still fire up and run on the artificial fuel supply. The engine would then die when the artificial fuel supply ran out. This has caused misdiagnosed fuel pumps, fuel pump relays, PCMs, and more when the technician failed to observe the theft light operation and also jump to conclusions.

The newer systems have included a starter interrupt into the PCMs strategies. So that the newer ones not only deny fuel, they also deny starter engagement. The PCM denies or authorizes the starter engagement by controlling the ground side of the starter relay. The ignition switch will supply positive power to the relay while in the start position and the PCM simply completes the ground if the key is recognized, or breaks the ground if the key is not recognized.

System Operation and Servicing

The exampled system here is from a 2000 Lincoln LS. This system contains the PATS module inside the instrument cluster. The scan data seen here is scanned from the IC. (see PATS Data 1 picture)

In order to be able to recognize what is bad about any system, we first have to know what is considered good. This first capture shows the PATS system operating as expected from a good system. Although this system does have a problem (well look at soon), it is working normally in this first capture so far.

Ÿ  Antiscan: The anti-scan is off. Anti-scan is a 20 second time period where the PATS or PCM will not scan key codes at all. This occurs when the PATS has been activated by sensing a key code that does not match one of the stored codes. This is part of the security strategies.