Service Procedures; Enabling; Vehicle Immobilizer System - Jeep 1997 Grand Cherokee Service Manual

8Q - 6 VEHICLE THEFT/SECURITY SYSTEMS

SERVICE PROCEDURES

VEHICLE IMMOBILIZER SYSTEM

WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO
RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
NOTE: The following tests may not prove conclu-
sive in the diagnosis of this system. The most reli-
able, efficient, and accurate means to diagnose the
Vehicle Immobilizer System involves the use of a
DRB scan tool. Refer to the Vehicle Theft Security
System menu item on the DRB scan tool for the
procedures.
The vehicle immobilizer system and the Chrysler
Collision Detection (CCD) data bus network should
be diagnosed using the DRB scan tool. The DRB will
allow confirmation that the CCD data bus is func-
tional, that the immobilizer receiver is placing the
proper messages on the CCD data bus, and that the
Powertrain Control Module (PCM) is receiving the
CCD data bus messages. Refer to the Vehicle Theft
Security System menu item on the DRB scan tool for
the procedures. Refer to 8W-39 - Vehicle Theft Secu-
rity System in Group 8W - Wiring Diagrams for com-
plete circuit descriptions and diagrams.
(1) With the ignition switch in the Off position,
depress the Lock or Unlock button of the immobilizer
transmitter. Listen for the immobilizer receiver to
issue an audible chirp (Unlock) or chirps (Lock). If
OK, go to Step 2. If not OK, replace the transmitter
batteries with known good units and repeat Step 1. If
still not OK, go to Step 2.
(2) Check the fuse in the Power Distribution Cen-
ter (PDC). If OK, go to Step 3. If not OK, repair the
shorted circuit or component as required and replace
the faulty fuse.
(3) Disconnect and isolate the battery negative
cable. Unplug the wire harness connector at the
immobilizer receiver. Check for continuity between
the ground circuit cavity of the immobilizer receiver
wire harness connector and a good ground. There
should be continuity. If OK, go to Step 4. If not OK,
repair the open circuit to ground as required.
(4) Connect the battery negative cable. Check for
battery voltage at the fused B(+) circuit cavity of the
immobilizer receiver wire harness connector. If OK,
refer to the Vehicle Theft Security System menu item
GROUP 8M - PASSIVE
STEERING COLUMN,
on the DRB scan tool for further diagnosis. If not
OK, repair the open circuit to the PDC fuse as
required.

ENABLING

The vehicle immobilizer system is disabled when it
is shipped from the factory. This is done by program-
OR ming within the Powertrain Control Module (PCM).
The logic in the PCM prevents the immobilizer sys-
tem from arming until the engine start counter
within the PCM sees twenty engine starts. The sys-
tem must be enabled when the vehicle is received
from the assembly plant.
The preferred method for enabling the immobilizer
system is to electronically advance the PCM engine
start counter using a DRB scan tool. Refer to the
Vehicle Theft Security System menu item on the
DRB scan tool for the procedures. Once this condition
has been met, the PCM will allow the immobilizer
system to arm.
If a DRB scan tool is not available, the immobilizer
system can be enabled manually, as follows:
(1) If five minutes or more have elapsed since the
last previous engine start, or if the vehicle immobi-
lizer receiver has been actively armed, depress the
vehicle immobilizer transmitter Unlock button. Lis-
ten for a single audible chirp from the immobilizer
receiver to confirm the Unlock message has been
received.
(2) Start the engine. Each engine start must be
followed by a minimum engine run duration of ten
seconds.
(3) Allowing a cool-down period between starts, go
back to Step 1 a total of twenty times. After twenty
cycles, confirm that the vehicle immobilizer system is
enabled by actively arming the receiver and attempt-
ing to start the engine. The engine may start
momentarily, but should stall above about 500 rpm.
CAUTION: Repeated sequential starts of the engine
to run up the PCM engine start counter and enable
the immobilizer system must be avoided. Overheat-
ing and damage to the starting system components
and wiring can result.
The same immobilizer system enable logic will
apply anytime the PCM is replaced with a new unit.
ZG