My 2012 Chevrolet Impala won't start

Odd as it may sound it is not unheard of to have a "new" battery and/or alternator to be defective, so these should be checked. Also recheck all wires and cables involved to be sure they are connected tightly and properly. Not sure if your OBD port will send data if engine isn't running but could be worth a try. Also, hit the starter with a hammer a few times. Seriously. If you have a solenoid on the starter it should be double checked. Previous answer is best place to start.

Security System:

• The vehicle's security system might be preventing the engine from starting.

• Test: Consult your owner's manual or a mechanic to troubleshoot the security system.

• Engine Control Module (ECM):

• A faulty ECM can disrupt communication between the various components, including the starter.

• Test: Have a mechanic diagnose the ECM using a scan tool.

• Faulty Wiring or Connections:

• Loose or damaged wiring can interrupt the electrical signal to the starter.

• Test: Visually inspect the wiring harness and connectors for any damage or corrosion. A mechanic can also use a multimeter to check for voltage and continuity.

• Immobilizer System:

• If your vehicle has an immobilizer system, it might be preventing the engine from starting if it detects an unauthorized key or a problem with the transponder chip in the key.

• Test: Consult your owner's manual or a mechanic to troubleshoot the immobilizer system.

Troubleshooting Steps:

• Check for Error Codes:

• Use a scan tool to read any diagnostic trouble codes (DTCs) stored in the ECM. These codes can provide valuable clues about the underlying issue.

• Verify Power and Ground:

• Use a multimeter to check for proper voltage and ground connections at the starter solenoid.

• Test the Starter Relay:

• The starter relay is responsible for sending power to the starter motor. A faulty relay can prevent the starter from engaging.

• Inspect the Starter Solenoid:

• Ensure the starter solenoid is functioning correctly and has a good connection to the battery and starter motor.

If you're unable to identify the cause, it's recommended to seek professional help from a qualified mechanic. They have the tools and expertise to diagnose the underlying issue. It's crucial to have a thorough diagnosis to identify the root cause of the problem. Replacing parts without pinpointing the issue might not solve the problem and could lead to unnecessary expenses.

All good answers above. You might also try the lock out safety function. The car must be in Park (maybe neutral) before it will crank. With the key held in "start" position try jiggling the shift lever back and forth fairly hard while in Park. Foot on the brake. Other than this, consider paying a mechanic to run a full diagnostic test. It will cost you, but not as much as the battery and starter. I agree that batteries and alternators have been faulty right out of the box so have them checked. Also you will find on the Web some sites where for a small fee you are connected with a mechanic who specializes in your brand of car. My wife's BMW had an issue in the drivetrain that the dealer could not figure out. I found a site for BMW mechanics, paid something like $35-45 and had a correct diagnosis in minutes. Be careful that you do not sign up for a monthly "service", just a one time deal. DId you or a friend put in the battery and alternator? If you paid a mechanic he should have got the car running one way or another. Go to AutoZone for example and look for a manual for your car. These are very detailed and help with diagnosing things. $20 bucks or so. Good Luck!