My 99 ford explorer won't start. When i turn the key, i get nothing. All my lights and electrical work. I suspect the anti-theft module under the steering wheel, because the "theft" light blinks when i attempt to start it. Is there an easy fix i can do myself?

chech and test fuse relay and connections === test battery [load test ] ---test starter and solenoid

Because you have changed the Module twice, (to the replacement one then back again), You will have made the ECU, (the car's brain), think it is actually being stolen. You'll need a Good Auto Electrician to look at you vehicle to sort this out.
Anti-theft units are coded specifically to the vehicle it is originally fitted to and only that vehicle so it can communicate with the ECU and the Key fob. That means they are not normally a part you can just swap. The only way to swap them is to pay the Silly prices and get a Dealership to re-programme the ECU and the Anti theft module to match your vehicle.

Anti-Theft -Passive Anti-Theft System (PATS) The passive anti-theft system (PATS) contains the following components:

• theft indicator
• encoded ignition key
• transceiver module
• PATS control module (located behind the passenger side air bag module)
• powertrain control module (PCM)
• standard corporate protocol (SCP) communication network

99 F-150 ignition/anti-theft question - Ford F150 Forum - FordF150.net

www.fordf150.net > ... > Electrical (Everything except audio systems)

Sep 16, 2009 - I had 2 keys for the truck, one worked perfectly fine, the other wouldunlock the ... over but the anti-theft light flashes and the engine won't actually start. ...Should I just spend the $80 for the switch and hope that is all it needs? ... for Fordkeys (Later 1998-newer Ford, Lincoln, Mercury) ... Mustang 1998 - 2001

electrical - Can I disable antitheft (PATS) on 03 Mustang ...

mechanics.stackexchange.com/questions/.../can-i-disable-antitheft-pats-o...

Jan 4, 2012 - So my question is: Is there a way to just disable the anti-theft system? ... This will make the car always 'see' a key with a chip. ... as they are usually intertwined with the anti-theft system to ensure the engine will not start. ... Where is the Wiper Relay/Control Module located on a 1994-1998 Ford Mustang??? 7.

How to Turn off Theft System on Cars: 7 Steps

www.wikihow.com > ... > Cars > Car Maintenance and Repair

wikiHowJump to Questions and Answers - Be the first to ask a question about this topic: ... Itwill not start and your battery will die. ... Reset a Check Engine Light ... Thanks to allauthors for creating a page that has been ... How to. Make Oat Flour. Cook Bacon in the Oven ... People are incredibly helpful and open to new ideas ...

The passive vehicle protection system will be activated and will disable the vehicle from starting if there is a:

• damaged encoded key.
• unprogrammed key.
• non-encoded key (key has no electronics).
• wiring concern.
• transceiver concern.
• PCM concern.
• module communications network concern.

Reset ? IF your anti-theft system light is flashing when trying to start your vehicle , an the engine doesn't crank , turn , or nothing happens when you turn key , then your anti theft system is at fault ! An trying to reset will not work ,you need to have it checked DTC'S - diagnostic trouble codes ,then fixed ! I suggest you have it towed to the dealer or a ASE certified repair shop !
PATS uses the powertrain control module (PCM) to enable or disable the engine. The PATS module communicates with the PCM over the SCP communication network in order to enable engine operation. The PATS module and the PCM use sophisticated messages in order to prevent a theft. The PATS and the PCM share security data when first installed together, making them a matched pair. After this security data sharing, these modules will not function in other vehicles. The PCM shared security ID is remembered even if the battery is disconnected. The PATS module also stores the vehicle's key identification code, even if the battery is disconnected. There are special diagnostic repair procedures outlined in this workshop manual that may be carried out if either the PATS module or the PCM needs replacement.

Do you have a question ?
Have you tried another key ?

My 2000 cavalier has done this for 6 months. You take your key out then open your door, wait ten minutes and the system resets itself and the car will start-annoying you bet!!!

take the positive side of the battery off for about 3 seconds and then put it back on to see if this will reset the security code

That's a very good posibility. If the anti-theft light flashes rapidly when you try to start the car with the suspect key, you will need to have a dealer program the keys. Good Luck and please leave rating.

Yes I agree it's the 'smart key'. Normally when you buy an explorer new, you will get 3 keys. 1 of the keys is a valet key.
If you were to copy another key that has a smart chip (transponder) in it, the new key won't work until you 'program' the third (new) key. To program it you need the original 2 keys that work.
The only other thing could be that there was a remote start in the vehicle and there could be something wrong with the module that bypasses the transponder. If there is a remote start in the vehicle you might be lucky to some extent if it still works.
If you move the shifter hard and it worked before, like you said, there could also be damage to the wires that goto the key cylinder, the reciever for the transponder in the key. Try having someone hold the key in start and use the tilt wheel, that too will tell you theres damaged wires if it starts.
Unfortunately you probably will have to bring the vehicle to a ford dealer to get additional keys programmed or the damaged part replaced.
It shouldn't cost too, too much. Just be glad you don't have a Saab, replacement key's are $145 Ea!
If your inclined, you can dissassemble the plastic shroud around the steering column and look for damaged wires coming from the black ring around the key down the the connector under the dash.