92 LS400 Alarm Woes

[nathanOJ]

I have a pearl white 92 LS400 that has been good to me for 6 years so far. I do not use the wireless remote key to get into it, so that means using the drivers door lock a couple times a day since this is my daily driver. The problem I have is the alarm going off when unlock the door. This means sticking the key in, turning to the right, then BEEEPP! BEEEP! BEEEP!! DAMN IT!! What is weird is that the alarm goes off sometimes, not EVERY TIME. Sometimes the door lock actuator tries to "fight" my hand turning the key.

So I took the interior panel off the door and pulled out the locking mechanism with the lock actuator in it, cause that's where most of the problems are with these LS's, right? I cleaned the lock actuator motor and that was a tremendous improvement, I tried cleaning the "contacts" where the actuator keeps it's positioning. I have replaced the "courtesy" switch as well but to this day it still goes off. WTH? What is tripping this Lex to freak out?!?  

That was my thought until I got in a minor accident... I had to change out the passanger door with all the locks and such with a salavaged door. I found my clue as to what might be wrong here. 

There is a switch on the cylinder lock by the handle that tells the car whether to lock or unlock the car. That's the end of the confusion. That has to be it. I'm guessing that lock sends the unlock message to the computer before the actuator knows what's going on. If that message doesn't get sent, the alarm thinks the door is getting jimmied open and throws a tantrum. There is a position sensor on the cylinder AND the actuator assembly; the cylinder HAS to send a signal before the locking actuator, otherwise it will freak out.

This is my hypothesis. Has someone else complained of this problem? Is this it? I don't want to throw parts at it and waste my time. 

Thanks.

[Exhaustgases]

I have a 90 with that same problem, I have not dealt with it yet. But I know the problem is with the key lock assembly and the switch there in. I don't know what happens to it, it could be both a corrosion issue and an out of an adjustment deal, like I say I haven't fooled with it yet. I have worked on the trunk lock though but that was dealing with stuck tumblers and such. If I remember the switch just removed from that assembly. And major problem with Lexus parts and even other cars they will not just sell you what you need, they have it all in a nice expensive assembly. Even things like power steering return hoses, you don't just get the little rubber one you need you get the steel pipe as well.

So its not a position sensor its more of just a switch since a position sensor is most always a variable resistor. I will check my manual and see what it is for sure if you need more info.

Oh and the courtesy door open close switches are most always the cause of the alarm going off when the car is just sitting, like at 2 am and waking up all your neighbors. I suppose the hood switch is part of that deal too.

[nathanOJ]

Correction: When I said "position switch" or "position sensor" for the actuator I meant limit switch or limit sensor. For the cylinder sensor, it's just a switch.

I still have the salvaged cylinder switch. It can be easily removed off the cylinder lock. It connects to the cylinder via a plastic flat head type connection. Then it has contacts VISIBLE for moisture to corrode. :/ 

[nathanOJ]

Well today I took off the door panel to get to the cylinder switch. Here are some photos to show what I mean. I cleaned up the contacts inside but there was some corrosion that I couldn't get off with some penetrating oil. The black stuff in the photos is completely gone, and I reflowed the solder to the traces in case there was a cold solder joint in there (yes, I may be crazy but I don't want to keep taking off the panel again). I slightly bent the rotating contact piece so there was more force on the contact points. The locks seem to respond when I got everything back together. I tried a couple times of unlocking the car after it armed. Alarm didn't trip yet. :) Time will tell if that was the fix.
 

Just be careful when removing the switch, very brittle. I have not broken it, but the door I replaced last month broke when I was swapping cylinders. Glad I had an extra :)

[sha4000]

I just changed my drivers door handle and had to remove the lock. All 3 wires attached to the cylinder broke off flush with the cylinder. I was real worried since I don't know what that connector controls. I put the door back together and tested all my lock functions with the remote key and everything worked as it always did. I'm wondering if that connector is somehow part of the security system. I have to test if the alarm sounds.

[nathanOJ]

11 hours ago, sha4000 said:

I just changed my drivers door handle and had to remove the lock. All 3 wires attached to the cylinder broke off flush with the cylinder. I was real worried since I don't know what that connector controls. I put the door back together and tested all my lock functions with the remote key and everything worked as it always did. I'm wondering if that connector is somehow part of the security system. I have to test if the alarm sounds.

Drivers door handle has an additional switch on it to turn on the keyhole light. Basically, in the dark, your supposed to pull on the door handle, it lights the keyhole, now you can see in the dark to where put your key without scratching the paint. Then theres an LED or light attached to the cylinder lock with 2 wires on the side to light the key hole. Then there are the three wires on the  very back of the cylinder that is used for the cylinder positioning. If the latter is broken off, you'll set the alarm off by unlocking only the driver door manually. And you can't unlock/lock all doors with it. Using the remote key will be no problem.

But anyways, I had almost a week of opening my driver side door with no alarm!! YAY!

[nathanOJ]

11 hours ago, sha4000 said:

I just changed my drivers door handle and had to remove the lock. All 3 wires attached to the cylinder broke off flush with the cylinder. I was real worried since I don't know what that connector controls. I put the door back together and tested all my lock functions with the remote key and everything worked as it always did. I'm wondering if that connector is somehow part of the security system. I have to test if the alarm sounds.

Drivers door handle has an additional switch on it to turn on the keyhole light. Basically, in the dark, your supposed to pull on the door handle, it lights the keyhole, now you can see in the dark to where put your key without scratching the paint. Then theres an LED or light attached to the cylinder lock with 2 wires on the side to light the key hole. Then there are the three wires on the  very back of the cylinder that is used for the cylinder positioning. If the latter is broken off, you'll set the alarm off by unlocking only the driver door manually. And you can't unlock/lock all doors with it. Using the remote key will be no problem.

But anyways, I had almost a week of opening my driver side door with no alarm!! YAY!

[sha4000]

On 5/19/2016 at 10:12 AM, nathanOJ said:

Drivers door handle has an additional switch on it to turn on the keyhole light. Basically, in the dark, your supposed to pull on the door handle, it lights the keyhole, now you can see in the dark to where put your key without scratching the paint. Then theres an LED or light attached to the cylinder lock with 2 wires on the side to light the key hole. Then there are the three wires on the  very back of the cylinder that is used for the cylinder positioning. If the latter is broken off, you'll set the alarm off by unlocking only the driver door manually. And you can't unlock/lock all doors with it. Using the remote key will be no problem.

But anyways, I had almost a week of opening my driver side door with no alarm!! YAY!

Thanks for that info. I don't need the lights and I lock/unlock with the remote. I was thinking of trying to resolder the 3 wires back onto the cylinder if it turned out to be detrimental to the operation of the car.

[Exhaustgases]

Craig, is it the same deal on the 98 or do you also have an older LS?

[sha4000]

On 5/22/2016 at 0:13 AM, Exhaustgases said:

Craig, is it the same deal on the 98 or do you also have an older LS?

Sorry for the confusion, I did not realize that he was commenting on a 92. I only have the 98 and there are only 3 wires connected to the cylinder that plug into a connector in the door.

[Exhaustgases]

I did that same fix a while back now. I used a very small screw driver to scrap the contacts and then put the same grease on them, it was a fun little deal to do. Had to hope things went back together ok and not fall out of alignment when doing so. Its worked just great since. I think they go bad from lack of use, either sitting too much or using the remote to lock and unlock the doors. Hmm also it could be from too much use and wearing the grease off the contacts. ?  Gosh any ideas?   Nothing else happening on this site. So looking at old threads.