Hi all. I did some searching, but didn't find quite this issue. Hoping somebody will have some ideas.

I have a '90 convertible. When I got it out this spring it all seemed good for a couple of days, but then developed a habit of the security system spontaneously activating. I'll start it, then after about 30-60 sec the horn sounds, lights go on, etc. Shutting it off does not help. Disconnecting the battery shuts it up, reconnecting it is ok until I start it again.

Based on other posts, it sounds like perhaps I've lost the cpu? But all the other ones made it sound like it would go off right away, rather than waiting a while.

Anybody recognize this issue, or have debugging ideas? Thanks in advance...

 

Looks like no takers

Gonna start looking for manuals. Are the chiltons/haynes ones any good for this class of problem, or am I better off getting one of the ex-dealer manual sets, like off of ebay? TIA...

 

Links for the FSM are in the FAQ. This one will have S5 wiring diagrams too: http://foxed.ca/foxed/index.php?page=rx7manual

I don't think the CPU will play a role with the alarm system, but you can verify in the manual. At least in S4s, there is an alarm control unit behind the glovebox. S5s may be different. You'll also have door, hood & trunk sensors, as well as the sensors somewhere on the door locks. If there is an intermittent connection at one of these points, the alarm control unit may interpret it as someone breaking in. I haven't gone looking for any of these sensors besides the ones on the doors. The same switches used for the interior lights are used by the alarm system to tell if the door is open or closed.

I used to occasionally have the alarm go off on my '87 TII, and the trick I used to get around it was to lock/unlock the door once, then lock it again and walk away. If I just closed the door and locked it, it might go off on its own.

 

I've had alarm problems in my black vert. What I've learned is that the passenger side lock mechanism is stiff and sometimes won't make it's full movement down to lock with the central locks. When that happens is when my alarm goes off. I imagine the alarm eventually registers something off with the door and starts going off.

 

My 91 vert had intermitent alarm problems that went away when a new cpu was installed(CPU is next to the fuse box).

 

Thanks for all the replies.

My car is definitely an S5, so no separate control unit behind the glove box.

Judging by the '91 schematic, the theft deterrent system *is* part of the cpu, which is what 6rotors said.

It sounds to me like I need to replace the cpu. Is there a source for used/repaired ones, or should I just see if I can get it from Mazda? Is there any point in trying to repair these things? It doesn't look all that complex...

 

i thought there was a body cpu that could be changed that solved the alarm issue? maybe it was the horn cpu?
I know its not the main CPU because I had a TII coupe that didnt had aftermarket ECU and it still had alarm issues and in another discussion is where I read about the body/horn cpu

 

Ecu = passenger side footwell
Cpu = driver side kick panel

The CPU may not control the alarm, but it does play a big role in alarm operation. I had my cpu re-soldered and upon reinstallation I discovered I had a factory alarm (center console and security light was missing).

I would imagine the signals for the door and other sensors pass first through the cpu for lights and what not and then to the alarm control module. Thus if the cpu is screwy, the signals might not make it to the alarm

 

so it must be the horn cpu right?

 

Yep!
Actually that's why I had my cpu re-soldered, to get my horn to work. The alarm was a bonus.

 

they are like $85 new