2003 Chevy Malibu

The most common failure in these is the ignition lock and the sensor built into it. The right thing to do is to replace the lock but it may fail again. I'm giving you a way to bypass that portion of it but the rest of the system has to be functional

Here's how you can bypass the sensor.

Go buy a 2.2k (2200 ohm) ohm resistor at an electronics store. Go to radio shack and just get one as close to that as you can. Remove the covers on the steering column and locate three small wires at the lock cylinder. Cut the yellow wire and the orange/black wire or on some vehicles, it's the yellow and black wires. Solder the resistor between those wires. Tape it up and put the covers back on and follow this relearn procedure. If this doesn't work you have a wiring problem in the steering column.
30 Minute Re-Learn Procedure
1. Turn ON the ignition, with the engine OFF.
2. Attempt to start the engine, then release the key to ON (vehicle will not start).
3. Observe the SECURITY telltale, after approximately 10 minutes the telltale will turn OFF.
4. Turn OFF the ignition, and wait 5 seconds.
5. Repeat steps 1 through 4 two more times for a total of 3 cycles/30 minutes ( the vehicle is now ready to relearn the Passlockà † Sensor Data Code and/or passwords on the next ignition switch transition from OFF to CRANK).
Important
The vehicle learns the Passlockà † Sensor Data Code and/or password on the next ignition switch transition from OFF to CRANK. You must turn the ignition OFF before attempting to start the vehicle.
6. Start the engine (the vehicle has now learned the Passlockà † Sensor Data Code and/or password).
7. With a scan tool, clear any DTCs if desired (history DTCs will self clear after 100 ignition cycles).