Strange SKIM module behavior question - JeepForum.com
 
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post #1 of 7 Old 08-21-2017, 10:08 PM Thread Starter
SouthernGypsy
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Strange SKIM module behavior question

A friend found a nice barn find on a 2000 model Sahara edition with a 4.0L and 5 speed, and un-known to him the sentry key system. It had been in storage since 2010 and was running when parked in a climate controlled garage but now wont so they had to trailer it home. After a bunch of testing we decided yesterday that it was the PCM had gone bad. However this evening without me there one of his neighbors who has a Jeep had an idea and well, well the guys created a new issue...

The neighbor with a 1998 model (Sport I think) with a 4.0L and 5 Speed so they tried his PCM on the 2000 model,. The No Bus error went away, the gauges started working, but it still only cranked without starting and when they checked with an OBDII reader it came up with a code for a bad Camshaft Position Sensor and a code P1685 for something to do with the security key. They didn't know what the security key was but looked up the Cam sensor online and discovered that the 2000 has one, and the 1998 has an old-style distributor so clearly that wasn't gonna work. Pulled the PCM back off.

Another friend had a 2003 model with a 4.0L but with an Automatic but the cam sensor looked the same so they tried that one, that one was back to the No Bus error on the dash, again cranked but no start, and when they read the codes they had a code for no bus to Transmission module which could be expected since the 2003 had an automatic, and again that same P1685 code to do with the sentry key.

Now. here is where it got more interesting. After they had already tried the 2003 model computer the guy with the '98 put his PCM back on his Jeep to go home and it starts but only runs like 3 seconds then dies. So checked his with the OBDII reader and has 2 codes, that same P1685 code for sentry key, and also another code (they forgot the number) for bus error with SKIM module.

The guy with the 2003 put his PCM back on, and his runs fine, no codes at all.


So then after some online reading one of the guys decided they needed to unplug the SKIM module from the 2000 model and plug it into the 1998 model just letting it hang under the steering column, tape one of the two sentry keys from the 2000 model to the sensor ring on that SKIM module and that would allow his Jeep to run to get home and figure out the rest tomorrow. Only, that didn't work, even after clearing codes with the OBDII reader and verifying they was erased, disconnecting battery again, etc. His 1998 model still will not run more than 2-3 seconds and those same two codes are back.

So after all this he then called me. After going over and working with them for over an hour I'm confused myself... I think I have heard plugging in a computer from a non-SKIM vehicle into one with a SKIM can cause it to start thinking there should be a SKIM even when put back on another Jeep, but why wouldn't moving the SKIM module to the other Jeep not then make it start when one of the code keeps was held close to the sensor ring?

Why didn't it affect the 2003 models PCM causing it to start having the same problem?

And and a bigger question is what can the guy with the 1998 model do to get his Jeep running again?

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post #2 of 7 Old 08-22-2017, 03:48 AM
Jonny Jeep
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Different communication is used for early and late models. CCD Bus Vs. PCI Bus. The change was between 2000-2001 models.

The SKIM in the 00 model won't have been able to communicate with the 03 PCM so it's unaffected by it.

The 98 could communicate with it so the PCM will now be programmed for SKIM. The SKIM should have been unplugged before trying the 98 PCM.

Options for the 98 are a replacement non-SKIM PCM with same engine and transmission (97-99 should work but 97 didn't have cruise programmed), getting the PCM reprogrammed to remove SKIM, fitting SKIM to the 98 and having it programmed with a DRBIII unit.
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post #3 of 7 Old 08-22-2017, 08:31 AM Thread Starter
SouthernGypsy
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Yea, they didn't even realize the 2000 model had a SKIM or what a SKIM was.

I've always heard the SKIM doesn't lock into a new PCM until three successful starts using the correct key for that SKIM, but they said it never started for them even once.


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post #4 of 7 Old 08-22-2017, 08:41 AM Thread Starter
SouthernGypsy
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What was the first year they had the Camshaft Sensor instead of a regular distributor?

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post #5 of 7 Old 08-22-2017, 09:23 AM
JEK3
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Quote:
Originally Posted by SouthernGypsy View Post
Yea, they didn't even realize the 2000 model had a SKIM or what a SKIM was.

I've always heard the SKIM doesn't lock into a new PCM until three successful starts using the correct key for that SKIM, but they said it never started for them even once.


~
Seems to me you can't just swap components around.

From the FSM:

The SKIS Secret Key is an ID code that is unique
to each SKIM. This code is programmed and stored
in the SKIM, the PCM, and the ignition key transponder
chip(s). When replacing the PCM, it is necessary
to program the secret key into the new PCM
using the DRBIII scan tool.

...

OPERATION
The Sentry Key Immobilizer Module (SKIM) contains
a Radio Frequency (RF) transceiver and a
microprocessor. The SKIM transmits RF signals to,
and receives RF signals from the Sentry Key transponder
through a tuned antenna enclosed within the
molded plastic antenna ring integral to the SKIM
housing. If this antenna ring is not mounted properly
around the ignition lock cylinder housing, communication
problems between the SKIM and the transponder
may arise. These communication problems will
result in Sentry Key transponder-related faults. The
SKIM also communicates over the Programmable
Communications Interface (PCI) data bus with the
Powertrain Control Module (PCM), the ElectroMechanical
Instrument Cluster (EMIC) and/or the
DRBIIIt scan tool.
The SKIM retains in memory the ID numbers of
any Sentry Key transponder that is programmed into
it. A maximum of eight Sentry Key transponders can
be programmed into the SKIM. For added system
security, each SKIM is programmed with a unique
Secret Key code. This code is stored in memory, sent
over the PCI data bus to the PCM, and is encoded to
the transponder of every Sentry Key that is programmed
into the SKIM. Therefore, the Secret Key
code is a common element that is found in every component
of the Sentry Key Immobilizer System (SKIS).
Another security code, called a PIN, is used to gain
access to the SKIM Secured Access Mode. The
Secured Access Mode is required during service to
perform the SKIS initialization and Sentry Key transponder
programming procedures. The SKIM also
stores the Vehicle Identification Number (VIN) in its
memory, which it learns through a PCI data bus
message from the PCM during SKIS initialization.
In the event that a SKIM replacement is required,
the Secret Key code can be transferred to the new
SKIM from the PCM using the DRBIIIt scan tool
and the SKIS initialization procedure. Proper completion
of the SKIS initialization will allow the existing
Sentry Keys to be programmed into the new
SKIM so that new keys will not be required. In the
event that the original Secret Key code cannot be
recovered, SKIM replacement will also require new
Sentry Keys. The DRBIIIt scan tool will alert the
technician during the SKIS initialization procedure if
new Sentry Keys are required.

...

NOTE: If the SKIM has been replaced with a new
unit, the Sentry Key Immobilizer System (SKIS)
MUST be initialized before the vehicle can be operated.
(Refer to 8 - ELECTRICAL/VEHICLE THEFT
SECURITY - STANDARD PROCEDURE - SKIS INITIALIZATION).
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post #6 of 7 Old 08-22-2017, 01:17 PM
mukluk
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Quote:
Originally Posted by SouthernGypsy View Post
What was the first year they had the Camshaft Sensor instead of a regular distributor?

~
The 2000 model year was the first to use a coil rail and cam sensor instead of a single coil and distributor, hence why the '00 wouldn't run with the '98 PCM.

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post #7 of 7 Old 08-22-2017, 06:34 PM Thread Starter
SouthernGypsy
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Quote:
Originally Posted by mukluk View Post
The 2000 model year was the first to use a coil rail and cam sensor instead of a single coil and distributor, hence why the '00 wouldn't run with the '98 PCM.

Yea, they didn't notice that until they had the no cam sensor code on the reader.


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