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

Toyota did the drawing, not me

only one box in your entire car has ~100 wires going to it (and 4 separate connectors to hold all of those wires) - that's the ECU
(which also controls the transmission and A/C)

if your ECU is working correctly, any OBD-II compliant scanner will work just fine, including AutoZone's and even this impressive $20 cheapie!

Yes, thanks Yamae.

I removed and disassembled the ecu. along side the ecm. behind the glove box with 4 black multi pin connectors.

it says toyota ABS & TRC & VSC 89541-50110
Denso 079400-7643 12 V
SV 89540 - 50110
100794-7424
and barcode.
I found ZERO evidence of capacitor leakage. Circuit board looks perfect. no smell, connections/wiring/pins perfect.

Could this be a module ecu for something other than the body?
abs- anti lock brake?
trc- traction control ?
vsc- vehicle saftey control?

I do have photographs. Not sure how to post them here..

Mike

99 LS400 wiring issues
 

Here are the 4 photographs of the ecu and capacitors.. all looks great ..

OK, I removed the MPX BODY module left of steering collum.

Removed cover, no signs of leaking capacitors or any melting burnt or abnormal looking spots on circuit board. Connections all good as well.

Also nothing under and around the steering collum looks out of place bad damaged etc.

NOW WHAT????

Guess I will put it in driveable fashion and limp on over for a scan attempt.

The label on this ecu/module is marked
TOYOTA 89221-50090
MPX BODY
123300-4186
DENSO 12 v
e13a-00 0039
e13020187

Wished my camera would take a very clear photograph for ya'll.

Hello ALL,

I removed both ecu's. The abs-tra-vsc ecu disassembled and inspected for capacitor leaks burnt spots, or anything odd in the connections and circuit panel. ALL good.
Also found the Body ecu near steering collum left side firewall behind fuse panel above left foot.
no obvious issues. A possible slight brownish discoloration on the insulator sheet between the circuit board and the body ecu housing (metal).Not burnt or melted. Circuit panel looks great.
Re installed and hooked up scan tool. NO SIGNAL..

A few of the things seem back to normal. The 4 ways /turn work properly now, the horn works normal, the door ajar light works properly for all doors. The seat belt light comes on now but goes off after car starts.Security light is also off now.
NO CODES No Communication.

Still, headlights not working on auto, wipers inop, door locks inop, mirrors inop, power trunk release inop.

Question; How can I get a signal from some computer on this car to give me a code or lead me in the right direction.

I saw a post about body ecu connector G34 pin3. Please help with more info about location this and testing it properly.

Thank you
Michael

I am trying to get scan tool to respond.

I have 4 wires at the OBD II connector
Black w gray 12 v
Yellow grnd
white w tracer grnd
white w tracer grnd

Why would a scanner not receive any signal at this connection?

1. an ECU can have bad capacitors and yet they look fine visually - mine did the first time I took it apart, and out of sheer frustration I pulled it out again 2 or 3 months later, even though everything had looked great, and by this time they were leaking and had almost damaged the main circuit board beyond repair.

2. you need to get the real Toyota factory service manual, for the step by step troubleshooting procedure on these problems that remain, so in other words, you get the door lock working or the wipers working or whatever, and you will likely get everything else working at the same time. you can buy the paper manual set on ebay for ~$200 if you want it right now, or sit back and wait and eventually find one for $75 - In the meantime, you can sign up for Toyota Information System and view or download whatever service manual pages are applicable for a 2-3 day unlimited period for only $15 - this is a service of the factory and required by law in USA.

3. to reiterate and earlier comment I made, I have never seen an ECU fail to communicate the OBD-II codes to a scanner unless the ECU itself had issues or else there was a power or ground problem to the ECU, which is easily checked at the connectors going to it, you will need something slend to measure the voltage and ground while it is connected (i.e. something like sewing needles)


PS - from what I can see in your blurry pics, the caps look OK visually, but this is no guarantee that they are good.

Hi,

I did use a volts ohms tester on the obd II connector.
Black wire 12 v
Yellow wire Grnd
white w tracer grnd
white w tracer grnd

I am well versed with mechanical repairs , however without manuals and scanner it can be difficult.
Dealing with the ECU issue i am uncertain if that OBD II scanner reads the ecm for the engine first? Wouldn't that be where trouble codes are stored?
Does the OBD II scanner read from the Multiplex body control ecu first/second/third?
Does the OBD II scanner read from the ABS, TRC, VSC ecu first, second, third?

Is there a resistance reading on the capacitors, so they can be tested while in the circuit board?

The battery goes dead now. So there is a circuit drawing that was not drawing voltage before.
Quite a complex problem.

If I buy a new mulitplex body control ecu, does it have to be programed at the dealer?

Thank you all for the continued support.

Mike

OK,

I have 12 volts and ground at the OBD II connector.
The Lexus dealer claims if the ECU is NOT responding to the scanner the ECU is defective.

At $2600 bucks I dont like hanging parts on to see if that will work .

Any advice, Please

www.car-part.com and/or ebay.

find a used ecu with a warranty.

1998 ls400 zero OBD II response
 

Thank you for the link to purchase a used ECM w CHIP, (some claim is a must)

There is NO warranty on electrical items, as i suspected. Understand perfectly.

This car is pssessed.

I have nearly the entire dash out now.
Car runs and drives ok.
horns work properly now
headlights work on manual only
door open light and location works good.

wipers work only on high but when first turned on run very slow and then all the sudden really fast. Sometimes gaining speed above the norm. inop on delay and other speeds. washers work good

both fuse panels are functioning properly
No obvious issues inside any of the 3 computers. ( no cap leaks, burnt, hot spots, connection issues)
ALL wiring and connections i have found look great. No mice issues with wires.
Checked several ground connections removed and installed back, all were clean and good.
inside dash and around engine compartment that i could find.

Seat belt lights dont work correctly,
power door locks/mirrors inop
flashers stay on all the time.

Every voltage, ground, ohms test on all i come in contact with has been good.

wth

Mike
mikeee1482us@yahoo.com

ps. I saw somewhere there is possibly an ecm relay...??????????????

:uh:HELP:woot:

just a heads up, you can't just replace a '97 or '98-00 ECU and expect it to work. Those years had immobilzers, and the immobilizer codes are stored in the ECU. So if you swap a new ECU, you would need to have someone with a Lexus/Toyota Scanner (usually a high end snap-on with propriety programming) to reprogram the ECU to your old keys. (Or, have the keys from the car your used ECU came from.)