Next few times you try starting, notice the car reaction step-by-step:
1: do the normal interior/door/dome lights illuminate when the door is opened?
2: without pressing the brake pedal, push the START button twice. Does the instrument panel illuminate?
3: Now hold the brake pedal down and press START. Did the engine try to start normally?
If the answer to 1 and 2 is "no" then the bug is likely poor connections at the battery. Slamming doors or the trunk lid is often enough to get flaky connections to touch enough to make the car start.
Aftermarket replacement batteries often have posts a little smaller in diameter compared to the factory battery so the wire clamps don't grip tightly enough even when the adjustment screw is bottomed out. Loosening the adjustment screw a bit and really shoving the clamp down, onto the battery, and then tightening the screw may help (force the clamp further down the tapered post); inserting a piece of thin metal as a shim between the battery post and the wire clamp can help too. Also, follow the negative (black) wire to where it attaches to the floor of the car - this is the primary ground point and if that screw is loose or the wire end is corroded the ground will be intermittent.
If the answer to 1 and 2 is "yes" but 3 is still a "no" then I would suspect an issue with the brake pedal switch (i.e. it is not realizing you are pressing the pedal) or the transmission park/neutral safety switch isn't seeing the shift lever in Park or Neutral so the engine is inhibited from starting - a safety thing. Push really hard on the brake pedal and try starting. Still nothing? With the dash instruments still lit up, push the brake pedal and shift from Park into Neutral and try starting... or go Park - Neutral - Park and try starting again. Pushing the shift lever fully forwards helps on some cars when the safety switch is somewhat mis-installed or is loose. The vehicle immobilizer might have triggered as well; try pressing the key fob unlock button twice and then try re-starting. Put the key in the dash slot (under the nav/stereo unit on early model year cars) or hold it against the START button (later model years) and try starting... if that works, the car is not "seeing" the key via the normal transponder mode; using the slot/holding it to the button uses the backup RFID mode. That bug can mean a bad battery in the fob (it won't lock/unlock the car from 20+ feet away if this is the case) or problems with the in-car fob detection receiver. On my 2009, hitting START when the fob is not detected generates an error message on the insturment cluster - do you see any error messages?
When you press the brake pedal while trying to start, how far does it move? Normally it depresses at least half an inch with moderate pedal forces but, if the car has been sitting a long time or the vacuum assist has bled off from the power brake booster, the pedal will be MUCH harder to push. In that case, you may not be pushing it far enough to actually trigger the switch that tells the computer "brake pedal is pushed" so the engine won't start - all that'll happen is the instrument panel will illuminate. An improperly adjusted brake switch can cause this too... and since many Genesis owners had that switch replaced recently from the recall there is a chance it isn't adjusted quite right. Mine wasn't - it was in too far actually so the car thought the brake pedal was still being pushed after I got out of the car: the rear brake lights were lit! Lifting the pedal slightly turned off the lights; I loosened the lock nuts on the switch assembly and backed it out slightly to fix the issue.
mike c.
