Friend's 2006 Civic immobilised after replacing battery?

[robbocop33]

My mate just replaced his 2006 Civic's battery,and after this his green key symbol is flashing on his dash and the car won't start?His doors open and closely remotely and his dash lights up with the ignition on,anyone any ideas?

[GreenV8S]

Sounds like your mate needs to figure out how to placate an alarm that has got upset. Sometimes it's as simple as putting the key in the door lock and holding it in the 'unlock' position for a few seconds.

[scott10005]

Hi, there is a cutoff switch under the dash, think it’s at the drivers side, it’s maybe activated itself

[redandwhite]

could be the intertia switch, at the end of the dash remove the panel & reset the switch - although only deployed if in a bump

[Butter Face]

Doesn't sound like the intertia switch, the green flashing light is normally an immobiliser light.

Is it an EP or FN civic?

[NMNeil]

Try a hard reset.
Remove the negative cable from the battery and cover the negative terminal to prevent mistakes. Touch the negative cable to the positive terminal of the battery and hold it there for about a minute. If it won't reach, use a length of wire.
Turn the ignition on and wait for about 5 minutes. Turn the ignition off and reconnect the negative battery. Hopefully this will fix it.
Inside the PCM, ECM, BCM etc are large capacitors and if you simply remove the battery cable you have only performed a soft reset as the capacitors are still charged and can maintain that charge for months. By connecting the capacitors directly to ground via the negative battery cable you have discharged the capacitors and reset the immobilizer completely.
Cost = $0