1999 LS400 wiring-security issue
 

Hi,

I have a 99 LS400 that has been perfect til now. I am not certain if I have a sercurity issue for some reason, or what causes the lights and horn to go crazy.

I started the car to warm up for 10 mins, loaded some christmas goods in back seat and trunk while the engine was running..
Drove about 4 miles .
The dome light, door open, 4 way flashers headlights, security light on dash ALL came on .

As well the HORN blows constantly.

I pulled over. read the owners manual and tried the door lock/trunk lock/ignition lock sequence to no avail.
Also , i disconnected the battery for 10 mins.

Same issue, lights stay on, horn on, unless battery disconnected.
I unplugged the horns and drove to the dealership.
After a visit to the LEXUS dealership - they could not get a response from the ecu/ecm.
NO codes/ NO communication.

On the way home I noticed the interior lights stay on all the time. The wipers are inop but the washers work. The 4 way flashers come on intermittently. The door open and seat belt lights do NOT come on at all. The door lock and mirror controls are INOP also.

I removed the glove box and checked a variety of wires and connectionsin the blower /heater box area and r kick panel looking for loose or burnt conditions. Fried relay or anything out of the normal range. All looked good.
Checked fuses and relays, Found no power to heated mirrors and headlights upper fuses. ???? Headlighs lower fuses good with power.

Any Idea's?????????????????

I am trying to travel back to Florida.
Your expert help would be truly appriciated
Mike
mas1482us@yahoo.com

ttt wiring issues

LS400 1999 wiring issues
 

While driving down the road my interior lights came on as well did the door open and seat belt and security lights. The horn sounded constantly.

The door locks and mirrows and wipers are inoperative.

The headlights stay on unless the battery is unhooked.

The Local Lexus dealership could not communicate with the obd,ecm,ecu.

Has anyone had crazy issues like this?

Thanks

Welcome to Club Lexus.

Sorry to hear, this sounds like a Multiplex Network Door Computer issue. I've read of these failing on Siennas but some of the symptoms are a bit different. Still within the realm of this ECM unit so I would check there first.

yes, I have had crazy issues, and one of the identical symptoms was "ECU will not communicate with any scanner, including the dealership's"

please read my extensive post and fix, it saved me a $2500 ECU replacement!

PS - mine is also a Florida car - I am starting to think that LS400 ECU's are particularly unforgiving of Florida's heat & humidity!

lol if it was the ECU he would likely have problems driving the car, but as he's stated it drives fine (hence he Drove it to the dealership.) This makes it far more unlikely a culprit.

I'll go with RA40's suggestion to have the body/muliplex ECU tested, and have the main harness checked for shorts.

so when have you ever seen the simultaneous twin symptoms of A) electrical things on car acting crazy AND B) ECU will not communicate with the dealership's scanners, and yet the problem turned out to be something BESIDES the ECU? - would be interested to hear of such a case. I agree that it is possible that a ground or short could do it, but that is exceptionally rare on a '99 unless someone has worked on the electrical system (i.e. aftermarket alarm, remote start, upgraded sound system etc.)

even if the issue turns out to be one of the subordinate ECU's to the main one, I have an exotic Old Rasputin Russian stout ale I am buying if the problem with that mini-ECU box is not also its capacitors! - same basic problem and essentially same fix!

Hi,

There has been no wiring tampering with alarms or remote starts. I checked every connection and wiring in the glove box area.

I am heading under the dash next.
Are you referring to the BODY control module ( left of steering collum) as the possible culprit?

The electrical issues get more bizzarre every time i drive the car, (which runs great)
emergency flashers stuck on now. Trunk pops unlocked while driving. seat belt light now comes on while door is opened , headights work normally now wit manual switch but not on auto, wipers inop,,, glad it is not the rainy season.

Thank you for any and all input..
Michael
mikeee1482us@yahoo.com

No communication sends up a flag. If the wiring up to the ECM is intact, this would tend to favor some part inside has gone south. One thing to try is unplugging it and see what symptoms are present. If it is the same as what you are experiencing, it is likely dead. Unfortunately it isn't like some $40-$50 small part and the cost of this ECM is going to hover ~$200.

Although RA40 suggested that it may be a Multiplex Network Door Computer but I think he wanted to mean the Multiplex Network Body Computer which is causing your problem. The Multiplex Network Body Computer handles the security horn, interior lights, trunk solenoid, head lights, wipers and etc working together with the ECU.

When the Multiplex Network Body Computer detects something unusual, it communicates with the ECU using the signal line "KSW" (pin 3 of G34 connector). I suggest you to check this line to confirm or simply just replace the Multiplex Network Body Computer itself.

To check inside of it visually sometimes help you to find the problem but it is all electronics circuits. It basically needs some special equipments and some skill to find the failed parts. If I were close to you, I could help you. If it were a capacitor issue, you could fix it easily just replacing them.

Anyway check inside of the Multiplex Network Body Computer.

Multiplex body control
 

Hi ALL,

I have not yet reached the ecu/body control module/mutliplex unit.
However I did a test of the fuses under the dash drivers side.
Discovered 40% of the fuses have NO voltage to them.
HUMMMMMMM

Digging deeper.
Are there any wiring diagrams available of the body control module ( what it looks like) so I can ohm and voltage test the wiring?

I did drive the car again. It runs fine. Noticed the security light is no longer on.
Is there a paperclip jumper trick to get the codes if any?
Maybe since the light is not illuminated I can get the computer to respond to a scanner?

Thank you for advice.
Mike

Keep in mind that many fuses will not have voltage unless certain conditions are present (car running or lights on, etc.)

there is no "paperclip" trick on a '99 that I am aware of, but many Lexus models (not sure about 99 LS) have a Toyota-style diagnostic connector in the engine compartment, probably with a protective cap on it. You would still need an appropriate scanner, and a cheap OBD-II scanner will not interface to this Toyota specific port.

I have, so far, never seen a case where the car would not talk to an OBD-II scanner and the problem wasn't the ECU itself (and by far, the most common ECU problem is the caps), but there's always a first time!

OK, after reading the full capacitor ordeal. I am going in that direction..
Nice drawing of the glove box area, but there are 2 computers side by side behind the glove box.
I did locate the hidden screw.. geesh.. Another access hole would have been easy.

I have replaced prom's in ecm before and can solider. So we shall see what has been leaking....
I am curious if the BODY control module on the drivers side has the same capacitors?

Wish me luck

Mike

the scanner connection (white with black cover)under the dash only has 3 pins in it. There cant be much more than voltage and ground for the scanner to communicate with.

I cant keep going to dealer @ 125 per hr to see if I found the communication issue.
Does anyone know if auto zone scanner will work on a nice1999 ls400?

thanks