Read the following paragraph from GM, this will give you some insight on the passlock system on your vehicle.
The electrical switching portion of the ignition lock cylinder assembly
is separate from the key and lock cylinder. The electrical switch
portion and the key and lock cylinder synchronize and work in
conjunction through the action of the mechanical assembly between the
The Passlock(TM) sensor contains 2 hall effect sensors. The tamper hall
effect sensor is on the top. The security hall effect sensor is under
the tamper hall effect sensor. Both of the hall effect sensors monitor
the magnet of the lock cylinder through an opening. The tamper hall
effect sensor is physically placed on top of the security hall effect
sensor. This arrangement enables the tamper hall effect sensor to engage
first if an intruder attempts to bypass the Passlock(TM) sensor by
placing a large magnet around that area of the steering column. There is
a tamper resistor inside the Passlock(TM) sensor in order to help
prevent tamper to the system. Passlock(TM) equipped vehicles
have a selection of 10 different security resistors ranging from 0.5K
ohms up to 13.6K ohms . Installing one of the security resistors inside
the Passlock(TM) sensor will generate a unique Passlock(TM) code. All 10
combinations of the Passlock(TM) sensor have the same part number.
BODY CONTROL MODULE
The body control module (BCM) contains the theft deterrent system logic.
The BCM reads the Passlock(TM) data from the Passlock(TM) sensor. If
the Passlock(TM) data is correct, the BCM will send a class 2 message to
the PCM to enable the fuel injectors and crank relay.
During the tamper mode the vehicle
may start. The vehicle will then stall. If the BCM receives the wrong
Passlock(TM) data, the VTD system will immediately go into the tamper
mode. The tamper mode will lock-out the vehicle fuel injectors and crank
relay for 10 minutes . The SECURITY indicator will flash while the VTD
is in the tamper mode.
If the Passlock(TM) sensor sends a correct password to the BCM when the
ignition is in the ON position, the BCM will send a fuel enable and
crank relay enable signal to the PCM.
The SECURITY indicator appears on the message center inside the
instrument cluster. If the SECURITY indicator flashes or if the SECURITY
indicator lights continuously during vehicle operation, refer to the
POWERTRAIN CONTROL MODULE
The PCM communicates with the BCM over the Class 2 serial data line.
When the BCM determines an incorrect password, it sends a Class 2 serial
data password to the PCM in order to disable the crank relay and fuel
injection system. If the BCM receives the expected voltage from the
Passlock(TM) sensor, the BCM sends a class 2 serial data password to the
PCM in order to enable the crank relay and fuel injection system. The
PCM then allows the vehicle to start normally.
FUEL LOCKOUT CYCLE
The Passlock(TM) system has a lockout cycle of approximately 10 minutes .
Once the vehicle is in the lockout cycle, the vehicle remains in the
lockout cycle for 10 minutes , even if the ignition switch is turned
from the ON position to the OFF position.
The Passlock(TM) system uses the lockout cycle in order to synchronize
all of the Passlock(TM) components when any Passlock(TM) related part is
replaced. The Passlock(TM) system requires 3 consecutive lockout cycles
in order to complete the 30 minute learn procedure for a changed
CHANGING THE PASSLOCK(TM) COMPONENTS
The design of the Passlock(TM) system is to prevent theft even if the
various theft deterrent parts change. The parts that can no longer be
changed without the possibility of going into a tamper mode are:
* The Passlock(TM) sensor
* The BCM
* The PCM
If you replace any of these parts the vehicle may not start for 10
minutes . This is the long tamper mode. If this occurs, the system must
go through a long tamper mode cycle. During this time the SECURITY
indicator will be flashing for the full 10 minutes and DTC B3031 will be
set. The BCM and the PCM require the full 10 minutes in order to
complete a learn cycle. The ignition switch must remain in the ON
position until the SECURITY indicator stops flashing. You will need to
repeat the cycle if the ignition switch does not remain in the ON
position. When replacing any of the above parts, perform the Programming
Theft Deterrent System Components procedure.
The design of the Passlock(TM) system is to prevent the vehicle
operation if the proper ignition key is not used in order to start the
vehicle. The mechanical key, in normal operation, will turn the ignition
lock cylinder. The Passlock(TM) sensor monitoring the position of the
lock cylinder will relay the Passlock(TM) data to the body control
module (BCM). The BCM will determine the validity of the Passlock(TM)
data. The BCM will send a password to the powertrain control module
(PCM). When the PCM receives the correct password the PCM allows the
crank relay and fuel injectors to operate normally. The Passlock(TM)
system requires the PCM and the BCM to communicate the various functions
in order to operate. These functions transmit over the class 2 serial
data line. For an explanation of the class 2 serial data description and
operation refer to Data Link Communications Description and Operation
in Data Link Communications.