OldSurfer

01 RX300 AWD 173k

no DTCs

no driveability issues

Hello, hoping someone has seen this combination. I dug through my wiring diagrams but could not find a common element.

All this worked yesterday...

Then it rained hard overnight, found driver's side well is wet. Cannot see any leak source, but did find the sunroof drain plugged, blew that out. Examined everything I could see or feel under the dash, no wetness trails or hints. (That blockage might not be new, it's my wife's car, she doesn't notice things.)

Issues: Temp gauge stopped working. Vehicle coolant is heating properly however.

Key in On position, CEL lights up, no AT temp light, no battery light, no oil pressure light.

While running:

Dash PRNDL has no indicator (again, runs and drives fine, monitored with scanner).

Radio HVAC display has no info, although at first it did have radio info. Radio plays.

The no seat belt light not working.

Power door lock switches not working both driver and passenger. Windows function fine.

The closest thing I could find was this https://www.clublexus.com/forums/rx-...t-working.html where a liquid spill under the driver seat was thought to be at fault. Under the seat, however, it is dry, but I don't know if the seat module is elevated or recessed under the carpet. Never been in there.

I have checked all the fuses for a hint but none were fried. The battery is good. I have disconnected it to reset the computers but that had no effect.

Everything else seems to work. Blinkers wipers sunroof hazards headlights etc.

Does this ring any bells for anyone? I would likely next pull the driver side seat and carpet to see if there is a source for the water but doubt all those dash indicator failures route through there. Or maybe just pull the cluster and look back there with a mirror for intrusion.

I did get the PRNDL to flash on once before during a brake so I 'am guessing" the circuits to the display and window locks still work, but something is loose or obstructed or there's some odd ground issue.

I just couldn't find a common circuit for those things. And at first, the dash would not light at all but that came back.

Thanks much, can't imagine someone has't seen this before.

-g

salimshah

Going on a hunch here ...

There is the fuse box directly under the front pillar. Water intrusion can cause all the instrument cluster to act up.

Note position of each fuse, pull them out. Get a hair dryer and use low heat to dry out the box, Wipe each fuse terminal and apply electrical grease and re-seat the fuses after giving enough time to air dry.

Salim

OldSurfer

Thanks, that's a good hunch, I stuffed paper towels overnight in likely intrusion spots to see if the continuing rain gave me a clue this morning as to the path, but no luck, all dry.

Will start drying components/connectors one by one, looks for changes or something. Thanks again.

bordenj66

So I am having almost identical symptoms, also started yesterday/Friday. Drive to work all is fine. In the afternoon the passenger doors wouldn’t unlock either with the fob or pressing unlock from inside the cabin. The back door lock does respond but only to the fob. Some dash indicator lights don’t come on, the engine temperature indicator stayed on C, pushing the ECT button doesn’t engage the ECT Snow light in the dash, and only the drivers side window and moonroof function.

This morning when I started her, everything worked again. Drove to the library. When leaving the library, same list as above again not working.

Battery voltage checks out ok. Disconnected battery for fifteen min, no change. There is no water damage or moisture. No sign of blown fuses, and the list above spans several fuses.

I hate electrical issues. Body and mechanical I can deal with.Thoughts appreciated.

Margate330

Hi friends, sounds a lot like Body ECU failure or a problem in the Multiplex Bean communication when multiple modules shows erratic behavior.

All of the body's modules are linked together using the MPX data wires on each module.
Modules are found in door locks & windows, memory mirrors, seats, dash cluster, AC, Info Display, sunroof, etc.

If you figure it out please share your fix.

bordenj66

Ok so I’m looking for resources for diagnostics. The two main resources I have (links below) don’t seem to include the diagnostic sections for the multiplex system, and it is recommended to check there first before tackling body ECU.

Does anyone have a link to diagnostics sections covering the multiplex comms system?

Links:

https://m.box.com/shared_item/https%...browse/9328827


https://s3cf792cad773e861.jimcontent...odes%20DTC.pdf

Margate330

Ok please clarify some things before digging into the multiplex system and can start with something more simple.

Can you unlock the doors and roll the windows down using the switches on the passenger side front door and the rear doors?
If so this is probably not the multiplex for a failure here.

However, if using the master switches on the driver side front door is failing to roll the windows down & lock doors on passenger side front and rear doors, it can be the multiplex and I'd start with the driver side door switch/ecu first and unhook the plugs from it and see what happens and if things go back to normal for dash cluster, etc.

OldSurfer

UPDATE/POSSIBLE SOURCE
I wrote here about thinking I had found the source, but the change in behavior when touching these two connectors was not the root cause. The problem returned.

salimshah

It seems you have inherited the problem and it was addressed in the past by excessive di-electrtic grease, but the source of the problem was never addressed [water intrusion]/redirection. I would go one step further by encapsulating in plastic wrap ... but I would also try to fix the bad contacts in the connector by taking all the pins out and cleaning/replacing the bad pins. Lexus parts sells the pins too but you can get the connectors from a junk yard.

Salim
ps: I think I have come across a post that mentioned the same connector damaged by water intrusion.

Margate330

Awesome job and thank you for sharing your fix!

It appears the multiplex data communication wire runs from the Driver Door Master Switch/ECU thru the IC1 junction(in your pic) to the Combination Meter ECU(dash cluster) and then to Instrument Control Panel ECU, etc. Other Body ECU wires may also be running thru here but the data wire connecting the ECU's together is critical for data integrity and communication and can cause multiple system/ecu failure.

PS- You saved yourself a fortune diagnosing this yourself since intermittent electrical problems are the most difficult kind to track down. Multiple trips to the repair shop at $100+ per hour is what happens to most people.


Here is the path connecting the ECU's to the Body ECU and special attention to junction IC1.









Location of the junction IC1 plug.

OldSurfer

This is great info Margate. Unfortunately, noted above, we ran into the same issue a few drives later. I think I'm going back in to check pin fitment next, there really was a lot of grease packed in there. Thanks for the diagrams.

Margate330

Aw darn I thought you fixed it.

I updated the pic above to show the full path of communication.
In that plug is the data wire coming to and from the Driver Door Master Switch/ECU- as can be seen a bad connection at IC1 breaks the loop for the multiplex.

*Note- the data can travel in either direction as shown by the arrows down the MPX wire in a loop so most ECU's have 2 paths so I'm not suggesting a loop break for multiple random symptoms, just that a poor connection can disrupt data integrity and cause glitches and one of many things that can go wrong and all ECU's/modules can be affected.

OldSurfer

UPDATE / POSSIBLE FIX

Moving up from the blue connector in my first photo, there is a female to female union in the image below. It's not marked but I circled it. It's also open in each end to possible intrusion, I found green crusties joining two of the terminals. The RX is operating again fine, but I've been down a couple rabbit holes, so am just waiting to see.

Thanks all.




the pins inside, corrosion had grown betw 2 of them




We will see. Thanks

Margate330

That would be the J3 & J4 junction if I read the diagrams correctly.
There is a lot of circuits going thru that plug.

OldSurfer

Going to call this a fix. Been using it solid and no returning issues. Thanks again for the help.