Is it possible to switch out the complete ignition from one 2002 alero to another of the same kind. i'm affraid ill set of a security code.

IS their a certain part on ignition switch that could be faulty ????? Rather then looking to replace parts that may not fix the problem ,take an have a scan tool hooked up an have code's in the BCM - body control module .Qualified repair shop. The BCM controls the anti-theft . Not to auto zone or pep boy's or advance etc. They can not read BCM code's .
Passlock?"¢ System
The Passlock?"¢ System is provided in order to prevent vehicle theft if the ignition lock cylinder is forced to rotate or the ignition switch is operated while separated from the ignition lock cylinder case. If starting is attempted without authorization from the Passlock?"¢ System, the powertrain control module (PCM) will disable engine starting. Start disable may be in the form of fuel disable or starter disable, depending on engine application.
The components of the Passlock?"¢ System are as follows:
?€¢
The ignition lock cylinder and key

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The ignition lock cylinder case, including the Passlock?"¢ sensor

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The ignition switch

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The body control module (BCM)

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The security indicator on the instrument cluster

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The powertrain control module (PCM)

Do you know what DTC'S - diagnostic trouble code's are
DTC B2947 DTC B2948 DTC B2957 DTC B2958 DTC B2960 DTC B3031 DTC B3033 DTC P1626 DTC P1630 DTC P1631 DTC P1632

Not sure I follow your question, but you can change the lock as long as you get a key blank that matches the chip in the old key.
The lock cylinder only holds the sensor for the chip in the key.

If you know that your battery, starter and ignition are working properly then continue on to possibly disabling the security system which is a known fault with Olds Alero from a failed passlock sessor.

You left something disconnected is my best guess. Look under the dash and see if the ignition switch is connected completely.

TO REMOVE IGNITION.FIRST TURN OFF RADIO.TO KEEP FROM LOCKING IT OUT.REMOVE NEGATIVE BATTERY CABLE.WAIT 20 MINUTES.THIS WILL DISABLE AIRBAGS.ALLOW THEM TO DISCHARGE.NOW YOU HAVE TO REMOVE THE INSTRUMENT CLUSTER.REMOVE THE TWO SCREWS SECURING THE IGNITION SWITCH.PUSH THE SWITCH ABOUT 1 INCH STRAIGHT BACK TO CLEAR THE MOUNTING BRACKET THEN LIFT IT UP AND OUT FROM BEHIND THE INSTRUMENT PANEL.DISCONNECT THE IGNITION SWITCH ELECTRICAL CONNECTORS AND THE IGNITION INTERLOCK CABLE.USING THE KEY TURN THE LOCK CYLINDER TO RUN AND PRESS IN THE PIN TO RELEASE THE CYLINDER THEN WITHDRAW THE CYLINDER WITH THE KEY.THE CYLINDER MUST BE REMOVED TO REPLACE IGNITION SWITCH BECAUSE YOU HAVE TO DISCONNECT WIRE TO THE IGNITION SWITCH. IN ORDER FOR CAR TO START YOU HAVE TO REPROGRAM NEW IGNITION SWITCH TO THE BCM AND PCM.TO DO THIS.TURN IGNITION SWITCH TO THE ON POSITION WITH ENGINE OFF FOR 10 MINUTES WATCH THE SECURITY LIGHT. WHEN SECURITY LIGHT EXTINGUISH.TURN OFF SWITCH FOR 5 SECONDS THEN START THE ENGINE.IF STILL DONT WORK TRY THIS PROCEDURE TWO MORE TIMES.IF YOU GET CAR RUNNING CHECK ENGINE LIGHT TURN ON CHECK FOR CODES P1630 P1631 P1632 USE CODE SCAN TO ERASE CODES IF CODES REMAIN LET DEALERSHIP CHECK IT OUT.THEY WILL HAVE TO ERASE CODES AND REPROGRAM THEFT SECURITY SYSTEM.

TURN THE IGNITION SWITCH TO THE ON POSITION FOR 10 MINUTES WITH ENGINE OFF.UNTIL SECURITY TURNS ITSELF OFF.THEN TURN OFF IGNITION SWITCH WAIT 5 SECONDS.THEN START THE ENGINE.IF SECURITY STILL ON DEALERSHIP HAS TO FIX.

SOUND LIKE THE THEFT SECURITY PROBLEMS. MOST OF THE TIME.THE IGNITION KEYS OR IGNITION SWITCH KEY LOCK CYLINDER WORN WHERE THE BCM AND PCM DONT RECOGNIZE KEY OR SWITCH SIGNAL.SO THE BCM AND PCM WILL GO IN THEFT SECURITY MODE.THE DEALERSHIP WILL HAVE TO FIX.BECAUSE IF THE KEYS , IGNITION SWITCH AND LOCK CYLINDER AND BCM HAS TO REPLACED.THEY WILL HAVE TO BE REPROGRAM USING DIAGNOSTIC EQUIPMENT. NOT A HOME FIX.YOU WILL NEED TO GET FIX SOON AS POSSIBLE.BECAUSE FAULTY SECURITY THEFT CODE WILL SHUT DOWN VECHICLE FUEL SYSTEM WHILE DRIVING OR IT WILL GET TO A POINT WHERE CAR WONT START NO MORE.THIS FIX WILL COST ABOUT $600.00.

Try replacing the ignition module...

I replaced the fuel pump and the fuel pump relay also the battery is new and its cranks but it is not starting. What do I need to do next? or replace? possibly since its a 2002 Alero, would it be the ignition switch?

the most common cause of this is the key, to check this use another working key, if the problem persists the ignition lock cylinder sensor is defective and the lock cylinder must be replaced, the dealer will need to do this as the security system must be re-programed to accept the new key code.