Headlights/ dash lights flashing

Make sure your tank is venting.

Check all the grounds for the running lights

David,
Do you have a part number or location/description of the part you replaced? I have the same problem.
John

sounds like an alarm system that has the horn disconnected,so when you start the vehicle it trips the alarm then resets itself after awhile .see if there is an aftermarket Alarm system under the dash and remove it!

Might want to check the fuses if you haven't already.

I would concentrate on the computer itself-also get onother opinion by doin a code scan again-the wiring inthe harness may hav faults-if ur tech minded go to sec 629 library

This may be the start of a worse problem that the Impala eventually developes. The Body Control Module has a design flaw along with the Passlock anti-theft system. You may get away with just replacing the BCM for now. It needs to be reprogrammed at the dealer and the car will not start if you replace the BCM without reprogramming it. I would also recommend against replacing it with a remanufactured one. Repair cost is going to be around $500 at the dealer.

If the Passlock system is also at fault, add another $500 for a new ignition switch and cylinder. If you haven't experienced random starting problems yet, they are coming soon. When you turn the key, nothing happens. I thought my 2002 Impala may have been immune to these problems that I've heard about constantly, however, at 90,000 miles, it became "possessed". The symptoms started slowly and got worse. Beside the interior lights flashing like strobs in the middle of the night (while the car was not running), the headlights would occasionally click off and on a few times while I was driving at night.

The relay switch you hear clicking is the Battery Rundown Protection relay. I'm suprised your battery hasn't drained to the point where the car will not start in the morning.

have to have the key reprogramed. you can try the 3 step cycle. turn the key to run for 10 mins than cycle to off and back on. you have to do 3 10 mins cycle

I have the same problem and now my car is dead.

i may be wrong at this but i think it's your alarm system. headlights, doors and horn all connects to an alarm system (if your alarm system does this) i mean, some alarms, when you unlock or lock your car, the lights turn and horn blows simultaneously with the alarm. if you have an alarm system that seem to malfunction, it may also affect your doors, horn lights etc. have it checked or replaced.

well, as ive said, i may be wrong. =)