Alarm battery replacement
My 1998 Astra Estate 1.8 CDX has a factory-fitted Thatcham 1 alarm. When turning off the ignition, there would sometimes be four chirps from the alarm, indicating its internal batteries were low. I was advised to remove the alarm, commonly referred to as a power sounder, while the ignition was on. It went off immediately, but died fairly rapidly because of the poor state of batteries. I opened the Bosch unit and fitted new Varta cells.
However, I don’t seem to be able to plug it back in again without it going off. I have tried various methods involving locking/unlocking, ignition on then unplugging it then reconnecting, but they all fail. The only way it doesn’t go off is with the battery disconnected and plugging it in, but as soon as battery is reconnected, it goes off.
There must be a correct method of recommissioning it – help! Alan Worland The sensors in the power sounder (PS) are designed to set off the alarm when a voltage drop is sensed. This is to prevent the vehicle battery being disconnected to disable the alarm. The sounder should be connected in the same state as when it’s disconnected, ie, ignition on. The alarm can sound when reconnected, but should stop after a short time. The PS will then be reset and operate correctly. This may be annoying to the neighbours, but if you have not given it a short time to settle after connecting, this should be tried.
If the same PS unit is fitted as was removed, the code should not need to be re-entered. If the unit was off the vehicle for some time and the job of replacing the batteries took a while, allowing the unit to totally deplete, then it is possible the security code (found on the code card of the vehicle) will need to be entered. This can only be done using Tech 2 software.
You do not mention if the vehicle will start. If it will, then it is unlikely to need coding as the immobiliser is being disarmed. If the vehicle will not start, the unit will need recoding. And if the vehicle does start but the sounder continues to blast out, the unit may be faulty.