S.K.I.M blues? ?    
Secuity Key Immoblizer module.  Introduced in 1999.  Or  SKIS.

SKIM Security key immobolizer module.   (aka, IMMO, SKIM or SKIS.)
Is the DASH SKIM lamp, stuck on?   This is a 2002 Grand Cherokee , later years, 2007+ the icon is just red light  and no words."stealth"

Can't start engine for longer that 2 seconds? and the dash SKIM Lamp is active?"glowing"  1992-1998 Jeeps have no SKIM lamp (key icon) and no SKIM IMMO key.

1999 to now  Starting and running. (nut shell list)  
 If the key is a real JEEP key  and gray plastic , it has the so called, CHIP (RF-ID) Transponder, key.    RF-ID means radio Freguency Identification.    RF-ID Key FOB's
1999 to now , for Jeep Cherokee or Grand Cherokee any other models...
Wrangler SKIM was optional in 1996 to 2001years.
 In 2002 to 2006, the FOB  must be programmed to your car. (PCM) In 2007,  you have the option for just a regular transponder chip ONLY key or a push button key FOB .
Jeep calls this FOB  a  RKE , for remote key entry, device.

If the SKIM is unhappy the ENGINE will not start, because the PCM drops the ASD relay.  (1 of 6 ways for ASD to TRIP  and fail)  The engine can run for 3 seconds. (don't let that fool you, scan it and see, "wrong key")
This is by DESIGN, the SKIM part, prevents all drive away no key ,thefts.
  • The Car came with 2 keys, transponder keys day 1.. (full featured RKE) try them both , please. (if one fails, it is bad key, if only door locks fail, on one key, it's a bad FOB coin battery)
  • 8 keys  programmed maximum. (limit) (only dealer has a cure)
  • On newer SKIM cars ,    (the dealer can program you SKIM to ban all lost keys, ever used in your car forever, max paranoia features) In truth nobody does this...
  • If a used key transponder, was programmed to another car, it will never work on your car.  (2007 and newer yes, older cars, I do not know ? read the FSM for you car.)  FSM means Factory Service Manual .
  • Do not have  2 keys or other transponder keys on your same key chain or near the igntiion switch,or they can cross talk and cause errors.
  • Do not have other large, metal objects on the key ring or it may block your transponders RF fields. (fails, until you correct this.. or is random failure.)
  • The newest FSM even names other RF ID keys, tags and such, that interferes with this Jeep system. So if you have troubles, remove all that STUFF from the cab. (and retest), sure turn off the CELL phone, . (and retest) Goggle Heterodyning....

If there are SKIM (IMMO) errors, the scan tool sees them!. and sets DTC's. Scan the PCM and do not work blind. win!  USE a real OBD2 SCAN tool ,like  the Innova 3160.
At key on, the dash SKIM lamp glows for 3 seconds as, a test.
Then  the skim lamp goes  out.  (on my new Jeep 08' the lamp is stealth mode, no icon no words there,, no shape just a red DOT)
If  the key is blank (new key) it enters program mode and flashes. (and a single tone) (if your key is bad, it might do this, and is a clue)
The skim also flashes for gross failures of the SKIM system.
It takes 2 good keys, to make a 3rd, never have less than 2 working transponder keys. Best is at least 3.  (I just saved you $180 in the future, with  you at dealer, and more, if towed there, lots more....)

If SKIM fails?
  1. Try the other Key. (I have 3 , not a choice, a rule)) I have 4th China clone key (fleabay junk) and it works electrically, but the case falls apart, at the slightest gingle..  (I bought real keys , by google searching with rear jeep part numbers, ON SALE)
  2. Check all fuses, if all keys fail.
  3. Unplug  the car starter battery (engine bay) negative cable lug, (you will lose the Radio/NAV codes (passwords, and cry later)  hit the home botton above and read how to un-Brick the radio. (all 6 ways)
  4. Then disconnect, the IGN. switch SKIM module, for 5 min. ( the FSM covers this location, as does all online Jeep dealer parts pages "drawing")
  5. Put the SKIM box plug back and then the battery lug back.
  6. This reset might work,  pray !
  7. A good skim system and   dead radio/nav  system, are ok casualties,  after the battery pull, is worth it, if car now drives ok.

Older Jeeps.
a spare key is $13 (early Jeeps) As seen here.

Starting in 2005 the cheap FULL FOB keys are $70-80
(I had to buy 1,  I had one original key and an aftermarket cheap one,(no buttons) (but very good) key ILCO  , they both work, so I got a dealer FULL FOB blank key and programmed it.)
Logic point 2,  if you have 2 working keys, at least buy a transponder only key, for cheap insurance (2 key rule). The system can't tell a full fob keys, from a key only keys. So all keys  countin the 2 key rule,  (a blessing)

Programming , takes two keys and is in the FSM chapter 8Q- page4 "customer learn" 
See below progam steps for user programming...

HACKS  (05GC) (extreme to easy)  (all rumor but in theory it sounds good , It does work with some years)
Carefully remove the rubber portion of the key. (I'd do that to a cheap transponder only key, no fob.)
Once removed ,you will find a white plastic holder with a transponder chip held in it.
Remove the chip from the holder and glue it to the inside part of the key shroud in real close proximity to the transponder antenna, that surrounds the front part of the lock cylinder.   (keep in mind, this kills the major theft deterrent part of this system)
It is a good idea to try random placings of the chip before making its new position permanent. (use a hot glue gun) (just plant it near the antenna ring, it will work.)
You can now just use , regular flat metal keys, that are dirt cheap $1.50  and I also like their small flat size, just right for a spare in your wallet.

HACK 2 )(best of best)  (PCM reprogramming for NO SKIM , NO MORE)
 Great for offroad only cars, etc. You  will be documented fully.

Warning 2:  Do not put your Wifes no SKIM PCM in to your SKIM active car or, you just bricked your Wifes PCM, bingo, two dead cars.
The act of plugging in your SKIM in to your Wifes PCM does that, so don't do it.

Key metal HELL.
Getting the metal key cut is hard,  many stores don't sell them, but can cut them.
So you must beg them to cut the key, using my blank,  1/2 the Home Depot's flat refuse. (they can not sell a blank, so can't charge you..so refuse you..)

At one Depot, I handed him my house key, then said, sell me a new house, key , and don't cut it please, but do cut my car key. ( or tip them , or bribe them...beg?)
and we made a deal.  (lets make a deal?)
All a royal PITA !!  All of this end to end.  ( It sure didn't lower my Insurance costs, not 1 dime.  I have 2 cars , one with , one without this  )
I think most of all this is gross paranoia...
On my car, a 2008, you must have the metal key part cut first or you can NOT program (learn/clone)  it.
The key  is not programmed, it's actually, learned by the SKIM.

The other hardware store in town is , Lowes, their index card, said use cartridge 11,  he didn't have #11.  off to the Depot. YMMV your Lowes will vary.

The transponder chip, works like a toll bridge transponder, just a shorter range. ( I used to repair them)
The chip is quasi- passive, and the antenna RF field wakes up a DC power supply (magic of RF rectification)) in the chip and the chip powers up, and then sends the rolling password. to the SKIM, I went to school on these chip systems (RF ID)
Someone as I type,just  hacked the system, they first jam the FOB then steals the FOB password, and then accesses the car, using your password. (hacked you are) There is a massive recall now.  This hack is called the Guy in the middle hack.
The battery in my Fob only runs door lock  buttons. period. and panic button.

My cheap key (no fob) is ILEC Y164-pt, DO NOT BUY USED KEYS , new is $13 period. Nor ever buy China clone keys, or cry. At the least, make this your 2nd and 3rd key, or LOSE !

end SKIM bull.

just my crib notes, now shared.

Programming: FSM 2008  paraphrased:  (my operators guide shows the same words, so read that glove box  guide first)
Customer Key Programming
If you have two valid Sentry Keys, you can program
new Sentry Keys to the system by performing the
following procedure:
1. Cut the additional Sentry Key Transponder blank(s)
to match the ignition switch lock cylinder key code.
2. Insert the first valid key into the ignition switch. Turn
the ignition switch to the ON position for at least three
seconds, but no longer than 15 seconds. Then, turn the
ignition switch to the LOCK position and remove the first
3. Insert the second valid key into the ignition switch.
Turn the ignition switch to the ON position within 15
seconds. After 10 seconds, a chime will sound.
In addition,

the Vehicle Security Alarm Indicator Light will
begin to flash.
Turn the ignition switch to the LOCK

position and remove the second key.
4. Insert a blank Sentry Key into the ignition switch.
Turn the ignition switch to the ON position within 60
seconds. After 10 seconds, a single chime will sound. In
addition, the Vehicle Security Alarm Indicator Light will
stop flashing. To indicate that programming is complete,
the Vehicle Security Alarm Indicator Light will turn on
again for three seconds and then turn off.
The new Sentry Key is programmed. The Remote
Keyless Entry (RKE) transmitter will also be programmed
during this procedure.
Repeat this procedure to program up to eight keys. If you
do not have a programmed Sentry Key, contact your
authorized dealer for details.

rev 4   ++++ 3-17-2014  (added year cut offs)