What's that on the dash?

[BudhagRizzo]

I have a '91 Previa LE. The fuse box cover in the middle of the dash has this little button-thing, and a wire clip on the underside of the cover that leads to it. For the life of me, I can't figure out what this is. Any ideas what it is (and will I feel stupid once I find out?) :)

[timsrv]

It's the "armed" light for the security system. When it's blinking you know the alarm is set. Tim

[BudhagRizzo]

Thanks! Didn't even realize this van had a security system. I'm gonna have to read up more on that.

[timsrv]

Yeah, the security system was optional (typically only came on some LE models). Unless there's a fault it should automatically arm every time you lock the van, then disarm every time you unlock (with a key). From what I understand, some Previas even had a keyless entry system (although I've never seen one). For keyless entry, I'm assuming you could arm/disarm with that as well.

Some things worth noting: These Previas have little sensors at every lock location. This is so the TD ECU "Theft Deterrent Electronic Control Unit" knows what's going on. Over time these sensors wear and corrode. The alarm will only set if the TD ECU gets the signal that all doors are shut & locked, so if you have a bad sensor the system won't work. Then there's the door open/close sensors & the ignition switch..........the ignition switch has a sensor to tell the TD ECU whether the key is in or out. Over time the ignition switch wears & doesn't always return to the "key out" position. When this happens the system will not allow you to lock the Previa or arm the alarm. The proper cure for this is replacing the ignition switch, but it can usually be kept at bay by wiggling the key a bit when removing from the ignition. The door open/close switches (http://www.toyotavantech.com/forum/showthread.php?1324-Open-door-warning-light-stays-on) that control the dome lights, also talk to the TD ECU, so if one of those has failed the system cannot be armed.

Here's some pics of a lock sensor:

http://i8.photobucket.com/albums/a23/timsrv/previalock1.jpg

http://i8.photobucket.com/albums/a23/timsrv/previalock2.jpg

http://i8.photobucket.com/albums/a23/timsrv/previalock3.jpg

http://i8.photobucket.com/albums/a23/timsrv/previalock4.jpg

These were taken of a Previa driver's door lock/handle assy....the last 2 pics are the interior of the sensor. These can get moisture inside the assembly (not uncommon). The moisture eventually leads to corrosion, which leads to no or intermittent continuity while turning the key. These can also become damaged or stuck in the wrong position.

The one pictured above had been damaged by moisture / corrosion and was not sensing correctly. If you look closely at the bottom picture, you can see a black mark in the middle of the left contact strip. This is a dead spot caused by corrosion. When 1st taken apart, the interior of this sensor was filled with green corrosion -- the picture was taken after the sensor was cleaned. In this case there was enough contact strip left to allow repair by bending the contact arm slightly outboard. This made the arm travel on a good portion of the contact strip. After the repair, the interior of the sensor was coated with dielectric grease, reassembled and put back into service.

You can check these with an ohm meter by disconnecting the harness from each handle assy, then check for continuity while rotating the key. There are 3 wires on each sensor (one common, one for lock, and one for unlock). If you're not getting continuity in lock or unlock positions, or if you're getting continuity when the key removed from that lock, then you have a problem with that sensor. Tim

[BudhagRizzo]

Humungous thanks for all the info. I think the previous owner disconnected all that because all the doors look like they've been all taken off and put back on for whatever reasons. I'm slowly finding out little things about this van. Thanks again! :)

[BudhagRizzo]

Update: So last week I locked up the Previa -- I usually don't, but last weekend I had all my band gear in the van. I went to unlock the driver side door and, to my surprise, the car alarm went off (I guess I do have a security system!) But I didn't know how to shut it off! I hopped in, put the key in the ignition and turned it. This killed the alarm, but I couldn't start the van! Kinda thinking about what you said, and working backwards (in desperation), I went around and manually unlocked all the doors, put the key in the ignition, and to my relief the van finally started up. This all totally caught me off guard! A friend later told me that, to disengage the alarm system, I should try unlocking the door, locking it, then unlocking again. Haven't tried it yet, but just wondering what your thoughts are on that little "trick". Thanks!

[timsrv]

It sounds as though a lock sensor (probably the one you used to unlock the van) is not transmitting the "unlock" signal to the TD ECU. When you opened the door the "door open" switch was activated but the TD ECU thought the door was opened without being unlocked from the outside 1st (it assumed somebody reached in through a broken window to unlock/open the door from the inside). To fix this issue you'll need to remove the driver's door handle & rework/replace that sensor. Assuming it's only the driver's door sensor that's faulty, you could get around this issue by simply unlocking the van from another door. One thing worth noting: The TD ECU requires a "double signal" from the driver's door before unlocking the entire van (this means unlocking with a key, returning the key to the neutral position, then turning to the unlock position again). This is a security feature to prevent the entire van from being unlocked if only the driver is entering. Unlocking the van from any other lock (except the rear hatch) will immediately unlock the entire van with only one twist of the key (assuming the lock sensor on the door you use is functioning correctly). Tim

[BudhagRizzo]

Thanks Tim! What you've just said all makes sense to me now. On another occasion before this, I tried locking the van up by going around, starting from the driver's door, to the hatch, side door, then passenger door -- with the key, mind you, because a couple of the door locks inside are a little flimsy. When I got to the passenger door and locked it, I went to test the side and passenger doors, and they had unlocked at the same time! It confused me at the time, but now with what you described, it makes sense now. I'll be sure to check out that sensor and get back to you (hhmm... it's probably why the "door open" light on the dash flickers every once in a while.) Thanks again, Tim!

[MondoVision]

I have a 92 Previa LE. The alarm started going off unprovoked this week. I suspect that when I washed my car some water got into the sensors in the door handles. I kind of hate the alarm system, so I didn't want to bother with cleaning or replacing the senors. After about of year of dealing with my unpredictable and untrustworthy alarm system, I finally figured out a way to disable it. Much thanks to this thread for all the alarm system details!

To disable the alarm system I disassembled the the rubber nipple looking sensor toward the bottom of the passenger door. I cut the wire and grounded it to the frame. This way, the door always appears to be ajar and the alarm can never be set. My door ajar indicator on the dash has never worked anyway, so I haven't experience any negative consequences from this work around. I can sleep easier at night knowing I can trust my Previa to stay calm, and my neighbors can sleep WAY easier at night now. That alarm was LOUD!

Thanks again Timsrv for this fantastic forum.

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