Stock 89 alarm trouble even after cleaning door sensors and other guides

[AaronB]

Forgive the essay, I wanted to be as specific as possible with my issue.

So I'm having trouble with my 89 factory alarm and hoping I'm forgetting something. I know I can pull the alarm computer and ground the wire but I would like to keep the factory alarm installed.

My driver key hole would never disarm so I would always unlock the car from the passenger side when I used the alarm. Recently I don't use the alarm so I lock the drivers door with my key from the outside, so the doors are locked but no alarm is armed. The other day I opened the drivers side door that was locked from the outside, and the alarm went off. After investigation it seems locking either door even from the outside will arm the alarm. I can shut it off via the ignition slot but the immobilizer is still active.

I tried all the reset tricks with turning the key and what not, still the immobilizer is set. I disarmed the alarm with the hatch key hole and it successfully disarmed, still wouldn't start. If I pull the dome fuse the car starts perfect so I believe the immobilizer is the culprit.

I pulled the driver door panel off, and pulled the cap on the back of the key hole that sets the alarm, it was dirty and I cleaned everything up, reinstalled, the car acts exactly the same. I unplugged the driver door alarm sensor and the car still acts the same except when I lock the driver door from the outside, it obviously will not arm because it's unplugged.

I'm just at a loss, I don't understand why the hatch will disarm the car but not the immobilizer, and why in the first place the key hole would arm the alarm when its supposed to only happen when locking from the inside. Unless I am not understanding how this system works. Thank you anyone who reads all of this.

 

[3p141592654]

The alarm knows the doors are locked because there is a switch in each door's "power-lock" solenoid that closes when the door is locked and this is separate from the switch in the key cylinder.

For disarming the alarm, the hatch key switch is on a separate circuit from the two door key switches, which are both tied together. So, if you cannot disarm the alarm with either of the door keys, then you need to troubleshoot those circuits.

At the junction box in the driver kick panel are two blue connectors with all the door wiring from the drivers door. The brown/yellow Arm wire is grounded when the key is locked. The violet-yellow disarm wire is grounded when the key is unlocked. You need to check that these are functioning correctly. They are shared by both doors. If one door shorts the disarm wire because of a fault, then neither door is going to be able to disarm the alarm.

Since you say the rear hatch key also doesn't disarm, then this points to a problem with the starter relay, or the alarm ecu itself. You should manually ground the starter relay blue-orange wire (pin 13 of the alarm ECU) and confirm correct operation of the starter circuit. If that allows the car to start, then something is wrong with the alarm ECU.


See the TEWD for details. http://www.cygnusx1.net/Supra/Library/TEWD/MK3/manual.aspx?S=Main&P=122

 

[AaronB]

Thanks so much for the very detailed response. From what you explained the alarm ecu will be my first test before checking the door power lock circuits. It's funny the hatch cylinder will disarm the alarm but the immobilizer will still be set ie. I'll unlock hatch, then door, get in like normal but no crank. Which I guess points further to the alarm ecu. Will report back when I know more, thanks again

 

[3p141592654]

I would check the starter circuit first. You could have a coincidental fault in the starter circuit that looks like an alarm problem. Its a simple test. Ground pin 13 (blue-orange) of the alarm ECU.

 

[AaronB]

Here's an update, mostly me being confused. I am very stupid when it comes to wiring so bear with me.

I went under the dash and found (I believe) the theft deterrant ecu. Found the plug with the blue/orange wire and unplugged it. Here's where I'm confused. That plug has 4 pins, and 5 wires going into it from the main harness. It doesn't match what I see in the tsrm being only 4 pins. Regardless I tried grounding it to see what would happen. I used a multimeter as a fused jumper cable, 1 end in the pin and the other on various metal spots under the dash. Had an assistant push the clutch and turn the key, no cranking. Did I completely mess up the test or does it point to a fault in the starter circuit. Like I said I'm very green with this stuff, trying to check everything before coming on the forums