cyfi66

Hey everyone, my LS400 has this issue that randomly appears and goes away. Most of the time, the locks will actuate properly, and lock/beep once when locking the doors with the fob; however, sometimes the locks will cycle twice when locking the vehicle with either the fob or the interior switch. Usually, it will have this behavior for at least a few days, and then go back to working normally.

It goes something like this:
Exit vehicle, press lock button once. Doors all lock, beep.....Doors all lock again, beep.

If I use the interior switch, same behavior without the beep.

I don't understand why this is happening, it also seems to prevent the interior lights from illuminating when unlocking the car as well. All of the door lock actuators are functioning perfectly fine, and all doors lock and unlock completely.

I have also had the alarm randomly activate twice in the past two months or so. Not sure what to try from here.

Yamae

That's what the door lock system works when one or more of the door lock actuator is failing. The twice means the retying. Search the Forum and you'll find ways to fix. The most expensive and effective way is to replace the door lock actuator. The most inexpensive way is just to clean the motor inside. But it is only effective when brushes and the commutator are still OK.

cyfi66

How does the computer know that the lock actuator is failing? Is there some sort of feedback that tells the computer that the lock actuated or not? Or does it look at the current draw?

The problem is that my locks are working fine, so I would have no way of knowing which actuator is going bad.

Yamae

Yes, there is a sensor in the door lock actuator each. When one of the sensors does not detect the stroke within the time limit, there happens the retrying.

cyfi66

I determined that my passenger rear door lock actuator was weak, and I replaced that actuator. The problem however still persists.

I am confident that the door lock position sensor is causing problems, I just don't know which door is the problem. All of the door locks actuate properly, but the car sometimes double locks because it has not received the proper signal telling it that the door actually did lock.

This is also causing my alarm to sound at random. For example, my locks will work fine and not double lock. Then in the night the alarm will sound, and afterwards, the locks will double lock for at least a few days. I assume that in the middle of the night, the connection in the door lock position sensor was loose and the computer thought someone unlocked the door manually which tripped the alarm.

Is there any easy way to figure out which door lock sensor is the problem? The only thing I can thing to do is remove all the door panels and check the continuity of the sensor pins in the door lock actuator while locking/unlocking the doors to see which one is not working.

If I knew which pins to check at the ECU itself, it would make diagnosis much easier and would prevent me from having to remove all the door panels. Is there anyone that could tell me where the ECU is located, and which pins correspond to the four door lock position sensors? That would be extremely helpful for me.

Banshee365

It will be somewhat difficult to test the unlock position switches without taking anything apart. Especially on the front doors. I don't have wiring diagrams for the 99 but my 95-97 diagrams MAY be similar. I've seen Yamae mention that the 98-00 cars communicate with a totally different language. The body control module is located left of the brake pedal and up on the firewall inside of the car. One of the connectors into the BCU has 16 pins. Pin 12 on that connector splices together in a junction box under the rear seat where the two wires from the rear doors come to meet. Pin 12 at the BCU is GREY. I suppose the BCU doesn't care which door is unlocked. It more just wants to see IF a door is unlocked when it shouldn't be back there. You should be able to see if either of the rear doors is showing unlocked by checking continuity through that one pin. Back probe it if possible. The grounds just goto your regular body ground all over the place. I'm sure you can find one near the BCU to use.

That is where the ease stops. The unlock positions are controlled by individual door ECU's for the front doors. From what I can tell the door ECU's put all of the info they receive into coded signals, sends those signals to the BCU and the BCU decodes them to see what is going on in those doors. You'll probably need to remove the front door panels to test at the connector at the BCU. There is an 18 pin connector on the door ECU's. Pin 3 on both doors is the unlock position switch. The other end of the switch goes to body ground of course. Those wires should be BLUE.

Of course, the 99 may be TOTALLY different.

Yamae

The way you want to try would be effective for Gen 1 and earlier Gen 2 models but after the bus system called Toyota BEAN was introduced for 98 and after, things became more complicated. You should be ready to analyse the multiplexed serial communication bus signals. Without doing so, you have no way to know which sensor is bad at the MPX Network Body Computer. Sensed signals are converted to a multiplexed bus signal which can't be simply analysed by an oscilloscope. In order to distinguish, you need a bus signal analyser specially designed for Toyota BEAN system. Without it, it would be quicker to monitor the sensed signal at doors although you need to remove door panels.

cyfi66

Thanks guys, I appreciate your input. I decided to go at it at the doors themselves, and I started with the drivers rear door (since I knew the passenger was good with the brand new actuator). I removed the door panel and tested the blue/white wires from the door lock actuator for continuity. What I found was that with the lock in the LOCK position, the resistance was around 18-20 ohm. When the lock was in the UNLOCKED position, the resistance was about 4-5 ohm. This was a red flag to me, because I know the connection should either be OPEN or CLOSED, not somewhere in between.

I removed the actuator and opened it up. The contacts for the lock/unlock position were coated with carbon laden grease. I cleaned the grease off, applied a light coat of new grease, bent the contacts to achieve a little more pressure, and then reassembled. After testing this time I get the desired results. Lock in the LOCKED position is OL (infinite resistance) and in the UNLOCKED position I read 0 ohm (closed circuit). I then reassembled the door and the double locking is gone! Hopefully that is the last of the random alarming. It seems that carbon within the grease was causing a partial short that would change resistance with the ambient temperature and sometimes get close enough to a short to signal that the door was unlocked and would set the alarm off.

Hope this helps someone in the future. I am glad I didn't have to go into the front doors, the rear actuator is really easy to access.

Banshee365

Blue and white huh? They definitely went with different colors on wiring starting in 98 then too. Good fix. It's great when the first shot from the hip lands a hit! Lots of big time problems can be fixed for free. You just have to have the knowledge and sometimes a little luck to know where to look.