P0125 sets when engine coolant temp does not reach temperature for closed loop operation within a set amount of time.
May be a faulty sensor or thermostat.
P0420 Is related to a faulty rear 02sensor.
P1518 PCM & TAC module communication detected missing or invalid serial data.
If TAC related repair has been done, clear DTC & recheck system. It may be necessary to preform clear codes function twice to clear this DTC.
make sure starting system & charging system are functioning properly. Low voltage can cause this DTC to set. This should help. Let me know how its going.
It is tied into the pass-key system that disables your car as part of vehicle security. You would have to by pass the pass key system which would make it vulnerable to theft as any duplicate key or broken ignition could start the car. In my estimation if it ain;t broke don't fix it or you might wind up with an inoperable car. There is more than mechanics involved ...codes and software programmed into the bcm will disable the starter, pump and injectors.
Go to this link. All the info you need to understand the system plus a few ways to near it on your vehicle
got old key place it on side of columb it should start
also try turning on ignition wait 10 min then start it should reset comp to except key but also check the manule
there is a way I've seen it done but never have done it myself. That "chip" is like a resistor for the anti theft system. When I asked the guy how he bypasses it, he stated, "I find the correct resistance needed, then add a resistor in line so that it bypasses the ignition switch." This way the orginal keys will work even if they don't have the "chip." Now the vechile he did that on he still had the key with the chip. The chip or ignition cylinder wasn't contacting each other so it would sometimes run and sometimes wouldn't. So I don't know if he tested the key or if there is a different way. I know this isn't much help but I KNOW it can be done.
The security is locked look in your vehicles manual to find the procedure to reset.