2002 f150 5.4 and anti thief light blinks ,wont start, replaced pcm relay, transceiver , pcm reprogrammed, still have problem every few days, wont start. then two hours later, starts fine, next?

https://ricksfreeautorepairadvice.com/ford-pats-antitheft-system/

You can't just change parts an expect it to work , software , modules won't let it work . You have to take it to the dealer or have a mobile lock smith fix it , reprogram it ETC...
Anti-Theft -Passive Anti-Theft System (PATS) The passive anti-theft system (PATS) contains the following components:

• theft indicator
• encoded ignition key
• PATS transceiver module
• powertrain control module (PCM)
• standard corporate protocol (SCP) communication network
• Passive Anti-Theft System (PATS) -Diagnostic Trouble Codes (DTC) Index Powertrain Control Module Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1213 Anti-Theft Number of Programmed Keys is Below Minimum PCM GO to Pinpoint Test F . B2431 Transponder Program Failure PCM VERIFY if using correct PATS key, if defective USE new key. B1342 ECU is Defective (EEFROM in PCM not working) PCM INSTALL a new PCM. REFER to Section 303-14 . B2103 Antenna Not Connected PCM GO to Pinpoint Test A . B1600 PATS Ignition Key Transponder Signal is Not Received PCM GO to Pinpoint Test B . B1601 PATS Received Incorrect Key-Code From Ignition Key Transponder PCM GO to Pinpoint Test C . B1602 PATS Received Invalid Format of Key-Code From Ignition Key Transponder PCM GO to Pinpoint Test D . B1681 PATS Transceiver Module Signal is Not Received PCM GO to Pinpoint Test E . - All Other DTCs PCM REFER to Section 419-10 .

Is the security light on or flashing when trying to start the vehicle .
Anti-Theft The passive anti-theft system (PATS) consists of the following components:

• Anti-theft indicator
• Encoded ignition key(s) (the key contains a transponder)
• PATS transceiver
• Powertrain control module (PCM)

PATS will disable the vehicle from starting if there is:

• a damaged PATS key.
• an unprogrammed PATS key.
• a non-encoded key (a conventional key or one that does not have any electronics).
• damaged wiring.
• a damaged transceiver.
• a damaged PCM.

If it is a anti-theft system you will have to take it to the dealer .This system will keep the starter from spinning the engine .

might wana have that theft turned off i had mine turned off on my 99 due to too manny problems i was like wtf so i had it turned off so now u dont need a key with a (chip) if u turn it off saves alot of time! down the road its stupid

you need to turn the key to the on position for 10 minutes then off for 10
minutes and then on for 10 minutes (a total of 3 times) the will reprogram your key it should start after this

if anti theft module not communication with scanner or diagnostic hook up then your vehicle will probably not start till thats corrected and clicking sounds like relay from security system opening up and shutting down power for starting system

Try turning the key from off to run ( do not start ) and wait 5 seconds, to see if the theft light on the cluster goes out.
If it does, check the fuel pump relay and the fuse for the fuel pump, and the fuel inertia switch in the passenger side kick panel.
If the light does not go out, as Ren1221 posted, try another key. If you do not have another key, you will need to tow it to a dealer or repair shop that can perform the erase all keys, and program 2 new keys.

DEALERSHIP HAS TO FIX IT.ANY TIME YOU HAVE PROBLEMS WITH ANTI THEFT SECURITY SYSTEM THE DEALERSHIP HAS TO REPLACE AND REPROGRAM CAR.IT COULD BE KEYS WORN BAD OR IGNITION SWITCH AND PCM CANT RECOGNIZE KEY.THE CAR WONT CRANK.

the anti-theft light is supposed to blink when the car is locked to show the system is armed.

Does it flash while driving?

Principles of Operation
The PATS uses a specially encoded ignition key. Each encoded ignition key contains a permanently installed electronic device called a transponder. Each transponder contains a unique electronic identification code out of over 18 billion, billion combinations.
The passive anti-theft system (PATS), also known as SecuriLock ®, uses radio frequency identification technology to deter a driveaway theft. This system is known as Securilock® in North America, Safeguard® in the U.K., and PATS in Continental Europe. Passive means that it does not require any activity from the user.
The SecuriLock® System (PATS) is not compatible with aftermarket remote start systems, which allow the vehicle to be started from outside the vehicle. These systems may reduce the vehicle security level, and also may cause no-start issues. If equipped the remote start system must be removed before investigation of PATS-related, no-start issues.
Each encoded ignition key must be programmed into the vehicle's powertrain electronic control (PCM) before it can be used to start the engine. There are special diagnostic repair procedures described in this section that must be carried out if a new encoded ignition key is necessary.
This system contains a new feature named Unlimited Key Mode. This feature allows a customer to program more than eight keys to the vehicle if they request it. Each vehicle in Unlimited Key Mode is set up with a special Unlimited Transponder Security Key. This allows all the customer vehicles to share the same keys, but no other keys from outside can be used to operate the vehicles. For an individual customer, any randomly selected Security Key is acceptable. Refer to Unlimited Key Mode Programming in Key Programming Switch State Control in this section.
The PATS transceiver module communicates with the encoded ignition key. The module is located behind the steering column shroud and contains an antenna connected to a small electronics module. During each vehicle start sequence, the transceiver module reads the encoded ignition key identification code and sends data to the PCM.
The control functions are contained in the PCM. This module carries out all of the PATS functions, such as receiving the identification code from the encoded ignition key and controlling the engine enable. The PCM initiates the key interrogation sequence when the vehicle ignition switch is turned to RUN or START.
All elements of the PATS must be functional before the engine is allowed to start. If any of the components are not working correctly, the vehicle will not start.
The PATS uses a visual theft indicator. The indicator will prove out for three seconds when the ignition switch is turned to RUN or START under normal operation. If there is a PATS concern, this indicator will either flash rapidly or glow steadily when the ignition switch is turned to RUN or START. The PATS system also flashes the theft indicator every two seconds at ignition OFF to act as a visual deterrent.
The following will activate the PATS and will disable the vehicle from starting:

• incorrectly encoded ignition key
• damaged encoded ignition key
• unprogrammed key
• non-encoded key (key has no electronics)
• damaged wiring
• damaged transceiver
• damaged PCM

This may be the start of a worse problem that the Impala eventually developes. The Body Control Module has a design flaw along with the Passlock anti-theft system. You may get away with just replacing the BCM for now. It needs to be reprogrammed at the dealer and the car will not start if you replace the BCM without reprogramming it. I would also recommend against replacing it with a remanufactured one. Repair cost is going to be around $500 at the dealer.

If the Passlock system is also at fault, add another $500 for a new ignition switch and cylinder. If you haven't experienced random starting problems yet, they are coming soon. When you turn the key, nothing happens. I thought my 2002 Impala may have been immune to these problems that I've heard about constantly, however, at 90,000 miles, it became "possessed". The symptoms started slowly and got worse. Beside the interior lights flashing like strobs in the middle of the night (while the car was not running), the headlights would occasionally click off and on a few times while I was driving at night.

The relay switch you hear clicking is the Battery Rundown Protection relay. I'm suprised your battery hasn't drained to the point where the car will not start in the morning.