Allante V8-273 4.5L (1991)
Lock Cylinder Switch: Description and Operation
Resistor sensing contacts are located in the Ignition Key Lock Cylinder. These contact the Key Resistor Pellet on the key when it is inserted. When the
lock is rotated, ignition voltage is applied through Fuse 14 to the PASS Key Decoder Module terminal A1. The Pellet resistance is then compared against
the programmed value in the Module.
If the Key Pellet is the proper resistance, terminal A3 is grounded, energizing the Starter Enable Relay. At the same time, a signal is applied at terminal
A2 to enable the Powertrain Control Module (PCM). When this signal is received by the Powertrain Control Module (PCM), it allows fuel injector
pulses to begin.
If the Key Resistor Pellet is the wrong value, the PASS Key Decoder Module will shut down for approximately 3 minutes. During this interval there will
be no output at terminals A3 or A2.
If the Ignition Switch is turned on again during this interval, the Timer will begin over again and the PASS Key Decoder Module will remain shut down
for another 2 to 4 minutes. The PASS Key Decoder Module will continue this process even if a key with the correct pellet is used to turn the ignition
back on. The Timer is restarted by the ignition voltage at terminal A1 when Ignition Switch is turned to RUN.
Once the Timer has completed its 2 to 4 minute cycle with the ignition off, the PASS Key Decoder Module and Timer are reset. A key having the correct
code can then be used to start the engine.
When the PASS Key Decoder Module senses ignition voltage at terminal A1, the Module will ground the THEFT SYSTEM ARMED Indicator for
approximately 2 seconds as a bulb check function. Should the key resistance not match the programmed value in the Module, the Indicator will remain
on. If the Ignition Key Lock Cylinder circuit is open or shorted, the Indicator will not light at all and the vehicle will not crank. The Theft Deterrent
Module also controls the THEFT SYSTEM ARMED Indicator during the arming sequence of the Universal Theft Deterrent System (UTD).
If there is a failure involving the wire from terminal A2 of the PASS Key Decoder Module to the PCM, or a loss of power or ground to the PASS Key
Decoder Module a message will be displayed on the CCDIC.
If the PCM does not receive the Cranking Fuel Enable signal, the "Starting Disabled..." message will be scrolled on the CCDIC.
If this message is displayed the key should be removed from the Ignition. The PASS Key Decoder Module will shut down for 2 to 4 minutes and the
vehicle will not start during this time period. If the Ignition Switch is turned ON during this time period, the Timer will reset and the PASS Key Decoder
Module will remain shut down for another 2 to 4 minutes.
If the PCM loses the Cranking Fuel Enable while the engine is running, the engine will not stall. If this occurs the "Theft System Problem.." message will
be displayed on the CCDIC and Code 58 will be set. Once the engine is shut off with this message displayed, it is likely that the engine will not start
again. This message will also appear on the CCDIC if there is a loss of power or ground to the PASS Key Decoder Module while the engine is running.
