How does the SKIM relate to the PCM? - JeepForum.com
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post #1 of 6 Old 02-21-2020, 11:18 AM Thread Starter
sdg3205
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How does the SKIM relate to the PCM?

I've always been a little confused about the SKIM interfaces with the other electronics in our WJs. Is it its own entity that can relay start information to any PCM/TCM/Computer in the engine bay, or is a SKIM module MARRIED to the rest of the car's computer modules?

You may have seen in my other post that I want to drop an 02 HO into my 01 non-HO and the information on the swap is shaky at best. Since I want the option to run regular fuel and the full benefits of the HO, my plan was to swap over the entire engine bay harness and PCM. Will the 02 PCM have any issues interfacing with my SKIM or anything else from my 01? If so, do I simply swap over the SKIM module from the 02 as well?

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post #2 of 6 Old 02-21-2020, 12:43 PM
Waterluvr
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The skim has two main functions in the WJ series Jeep, it stores the programming code contained in the security key(s) RF chip and when you crank the Jeep to start it the skim verifies the unique RF code via the antenna ring around the ignition cylinder.

After it verfies the information received from the RF antenna it also communicates with the pcm to confirm a married skim code that's programmed to both the skim and the pcm.

The pcm is the only other module it communicates with.
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post #3 of 6 Old 02-21-2020, 01:24 PM
WestKy
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Thats why I asked in my question "Sentry system" about selling all my "Key" parts as a group. I also read somewhere in the forum here or elsewhere that you can get your ECU reprogramed for about $150 so as not to require a skim sentry system.
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post #4 of 6 Old 02-21-2020, 03:00 PM Thread Starter
sdg3205
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About 18 years ago when we installed a remote start system, we had to glue a spare key to the skim module.

So in this case I could install the 02 SKIM module which is married to the HO PCM, glue a key to it and continue to use my old keys and FOBs. Seems like the best solution. Then my keys and door locks donít need to change.
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post #5 of 6 Old 02-21-2020, 03:16 PM
WestKy
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I did the same thing when installing a remote start because I could never get the immobiliser bypass function to work, so I sacrificed a $90* key the same way you did then kept a steel key in my wallet in case I lost the other transponder key so I could open the door and rip out the hidden one in a pinch.

*My jeep only came with one key so I had to have one cut for $30 then another $60 to have it programmed.
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post #6 of 6 Old 02-25-2020, 08:57 PM
ParkerStovall42
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Is the SKIM married? Kinda. The SKIM stores which transponder keys are allowed to start the vehicle independently from the PCM. From the factory, the PCM has no value stored for what the correct ID is for the SKIM installed in the vehicle. On first startup it will query the SKIM for it's ID, write that value to memory, and then refuse to allow anything that doesn't match to start the engine. What the various PCM rebuilders do is erase the block of memory that contains the SKIM ID so the PCM believes it needs to query the SKIM for that value just like a first startup which will marry whatever SKIM is present to the PCM. Or just allow you to run without one if you never plug a SKIM in.
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