coltking

Few weeks back my son left the rear passanger door open it drained the battery.So i obviously charged it carried on with the day.Next morning dead again ,charged it again .following morning dead again replaced w a new battery few days go by dead again .so i have found 4 amps of draw narrowed it down to the dome and mpx b fuse . My drivers door window controls not working aswell as seatbelt adjust memory power mirrors and dome light car is not seeing doors ajar either .ive inspected all wires running in rubber boot and all look fine and test for continuity from end to end .im in need of help please.

RA40

iTrader: (6)

I'll post this for any others that may look up this thread with a drain issue:

Since you've narrowed it down to those areas, what happens when you pull the fuse to that circuit? At the individual point, what happens when removing the bulb or unplugging the switch assembly? Check the door ajar switch on the door your son left open is my thought.

coltking

Well tried again today to find the drain .pulled ecu looked inside looks ok by visual.pulled body control unit looks fine by visual.removed rear door card and visually inspected and tested all wires removed rear door lock/ switch opened micro switch cleaned and checked for operation.so far all looks good. Still drawing .8 amp .open door draw is 1.2 amp somehow ive droped few amps maybe different tester used today ? Still no power mirrors ,dome light or notification that any doors are open pulled the 2 fuses under hood marked mpx b and dome .drain is down to .05 amp . windows still work by each switch without these fuses .is it possible for 1 bad mpx box to mess the rest?.anyone have a wiring scematic for 98 ls 400 body control unit .leaning towards the bcu or ecu just not sur if the ecu has any connection with the bcu

dicer

You will never find any kind of information on body control units or ecm's. If you ever do let me know where.
You can get fuse adapters that will allow you to hook up an amp meter to the various fused circuits to locate which one is doing the draining.

coltking

So last night went out for a ride about 45 min.upon returning the car had recognized the passenger door was open aswell as all door ajar switches working the power mirrors were back memory seats all controls on drivers door i tried putting in dome light fuse back in lights all came on put mpx b fuse in .same problems came back w all the accessories not working .pulled the fuses again w no luck of accesories coming back pulled the battery again and left over night ..going to test more soon .so my thought is somewhere in dome light wiring and mpx b wiring. Problem still exists .still looking for wiring diagram for the dome light cct? Anybody?

aptoslexus

Interior lighting diag.

Yamae

Your problem needs some one who is familiar to the MPX network system of UCF20/21.

The system has a communication bus and 5 controllers are sending signals each other via the bus named MPX. What I mean by controllers are 4 door controllers and 1 body controller. The system is rather complicated and usually a dealership just replaces those controllers when troubled. I know some about the system but I'm not good at explaining details in English. I worry that one or more of the system controllers is/are damaged and not working properly or the bus line is not functioning. But a simple battery draining should not damage the system.

I have 4 simple questions to ask you before I assume more.
Q1; Does the trunk opener switch work?
Q2; Does the steering tilt and telescopic work?
Q3; Didn't you have any seat memory problem before?
Q4; Didn't you disconnect any connector without removing the battery's negative cable while you were doing trouble shoots?

coltking

So today went had a friend hook up his snap on scanner it wont recignize the car .it did a month ago when my water pump fell apart said high temp of 272 .so it was working then now its not reading . another problem now is temp gauge works when wants to is it possible the ecu may be the culprit? Weird that all these options came back to life yesterday with the 2 known fuses which are drawing not even in .then put in dome fuse lights came on put in mpx b fuse lights went out .so i pulled mpx b out ..no lights so i pulled dome fuse back out.this is driving me crazy..and when the door open came on cluster the door light in bottom corner did not come on .yes memory for seats was working prior to this.also tried each connector at a time .connector on left on bcu will remove draw .had a electronics tech look at bcu and didnt see any shorts or opens.yes to all ur questions yamae thanx for everyones help.

coltking

If the ecu was at fault would it also affect bcu?

Yamae

Sorry that I have some difficulties understanding your writings. But I don't think the main ECU is the culprit.

What I worry about is that connectors were removed without disconnecting the battery. This often causes newer problems. Those controllers can't be checked by eyes nor by a simple circuit tester.

coltking

Hi Yamae not sure what to do at this point.is there any testing i can do to let you know what is going on.

Yamae

Would you answer my questions Q1 and Q2 for the fundamental judgement?

coltking

Yes.trunk opens fom inside car but not wity key button .yes the tilt and telescoping wheeel is still working.

Yamae

You need your key to press several seconds or more to open the trunk. Anyway the MPX bus line seems to be not dead judging from your answer. I would suspect that the black box inside of the door is partially dead. The black box is called driver's MPX network door computer/controller. The page 142 of the wiring diagram says it "driver door ECU". What happens if you disconnect it. Still you have a big current draw? Don't forget to disconnect the battery while you do the job.

A strange thing is that the scanner can't communicate with the main ECU. I just wonder why so.

coltking

Thank you Yamae for your time and help i will remove negative battery terminal then dissassemble drivers door to see if we get rid of the draw .I will reply soon.thanks again.can i just unplug door connection?or remove mpx ?