75ZT Community

I was bought a 75 a few days ago reporting that "The alarm keeps going off". He gave me the key, and using the keyfob lock/unlock buttons I locked the car, and within about 15 - 30 seconds the alarm triggered. I popped the bonnet switch off, = switch and connectors clean and dry (like new), all good with the multi meter, popped it back on again. 'That's me finished, good job too because it has stated to rain'. I Locked the car, same thing happened (uh). From the O/S front door, I went round opening and closing each door, tailgate, and tailgate window. When I opened the O/S front door I noticed the alarm led was blinking slowly (what!!). I Shut the door pressed unlock and the alarm led went out. As soon as I pressed lock the alarm triggered, and the alarm led immediately began blinking slowly, without the initial rapid blinking. There is no set pattern, I locked the car about 10 times and the alarm would either trigger as soon as I pressed the lock button, or shortly after locking, each instance the alarm LED (Light Emitting Diode) just immediately started blinking slowly.

Pressing unlock silences the alarm and unlocks the doors each time without a problem.

The alarm LED when blinking, seemed to blink slower than usual to me.

The 75 has had no electrical mods apart from a DD and digital tuner, and has always been bought to me for service. (ok say it if it makes you feel better).

I suspect the Alarm Control Unit has gone tits up. Any other offers.

Now where was I... ah yes.

Is the Alarm Control Unit plug and play?.

Could there be issues with the keys and rolling codes?.

Has anyone replaced an ACU and tadah?.

If I plugged a unit in from a MG Rover or Landy, would the original unit throw its toys out the pram more than it is already, if it is the ACU

Cold weather can affect the switches inside the latch that tell the BCU (Body Control Unit) whether the door is open or not. I had a problem on my green car where the passenger door would say it was open when it wasn't whenever the weather was as cold as this. It was usually OK until you opened and then closed the door. After that you had to wait until the car warmed up before it would behave properly. If you can get to a T4 (Testbook version 4.Computer Diagnostic System) it will tell you what the last items triggering the alarm were. Alternatively you could temporarily disconnect the door open wire for that door from the BCU.

The alarm control unit is actually the BCU. And no they aren't P&P. You need a T4 to copy the keys and ZCS codes across.

Thanks Duncan, I forgot to mention it gives the door open beep if the alarm is triggered with a delay when lock is pressed.

I cannot understand how an actuator issue could trigger the alarm as soon as the lock is pressed, without a door open beep, and the alarm LED blinking after unlock is pressed and all doors are opened.

T4 should be interesting with the alarm led blinking away, to me anyway.

There again I think I have given up on MG surprising me long ago.

Steve I would still go for the bonnet switch swap it over with yours and see if it makes any difference also turn up the rubber stops so bonnet is tighter, also spray some WD40 into the drives lock, easy way to remove the bonnet lock is two credit cars either side of the switch push in and lift out the switch.

Battery re-set might help also

Battery re-set plus--------------A brick resting on the bonnet switch, then try it.








PS.---bRought------------------Lol.------

Colvert wrote:Battery re-set plus--------------A brick resting on the bonnet switch, then try it.

Did that and that mate.

Arctic wrote:Steve swap it over with yours, also turn up the rubber stops so bonnet is tighter, spray some WD40 into the drives lock, remove the bonnet lock. Battery re-set might help also

Did that, that, that, that, and that Steve. Swapped my switch with his the next morning, and sprayed WD on all doors, as initially it was getting dark and was raining. He uses it for work so passenger doors are not frequently used.

I have told him to just keep locking it manually, until he can get it on a T4 to find out what is triggering it.

Devilish wrote:
I have told him to just keep locking it manually, until he can get it on a T4 to find out what is triggering it.

Steve drop Stef a PM or text and ask him if he as time to get it on the T4 before he goes back to work Tuesday I think ?