I have a 2001 RX300 that upon start up or when a door is open, the door open dash warning light does not go on. The dome light will also never turn off when in the auto position. The courtesy lights on the door itself do come on when you open a door. All other functions on the driver side door (windows, locks...)work. Can anyone give me an idea of how to fix this. Thanks.

 

Let me get this straight..
Engine running. Door open and no illuminated door open warning light in the dash...right?
Does the dome light stay on in the auto position even when all the doors are close?

Does this happen only on when the driver's door or any door?

 

Let me get this straight..
Engine running. Door open and no illuminated door open warning light in the dash...right?

Correct.


Does the dome light stay on in the auto position even when all the doors are closed?


Yes.


Does this happen only on when the driver's door or any door?

All doors and rear hatch too.

 

Kinda hard to diagnose electrical problems over the net and no wiring diagram. lol..
I'll try my best though.

Well lets start with the obvious.
I'd first check if the bulb for the "open door warning light" on the combo meter is not burnt out.
They must be in the same wiring since they probably use the same ground.
If the bulb is burnt. It won't be able to complete the circuit to turn off the auto dome light. (just my theory)
These multiplex systems run diff circuits but need to communicate with each other for them to work.

 

Bulb checks OK.

Thanks.

 

Alright.
Next thing you should check is power and ground to that bulb.

I think that this bulb has constant power to it with ign. ON.
Illumination is contolled by ground.

 

If I was looking at a circuit diagram I could possibly provide more concrete help. So take the following as general discussion.

Earlier each door switch provided a path to ground and the bulb was always fed +12v on the other side. Once the switch was released it would connect to ground and the circuit would complete.

Now the door ajar switch feeds the ecu. The ecu then activates the dash display and dome light. The ECU further has short and long delay (based on lock or unlock) and also has soft turn off. In Lexus the ecu senses the rotation of wheel and at certain speed makes a ding-warning if the door is open. In Lexus, the door ajar switch is part of the door catch mechanism along with the door lock actuator.

Back to the problem at hand,,, if all doors are failing then it is more likely that the problem is in the ecu or beyond (all the way to the bulb). If the on-door-off switch allows you to turn on the bulb, the the bulb is OK. Then we are left with ecu and wiring. Typically Lexus wiring and connectors are of good quality and if no one has messed with the wires then we are left with ecu. Which ecu controls the light bulb cab be answered by looking at the circuit diagram

Out of desperation, you may like to disconnect the battery for 20 minutes or so. [Again all the above is based on what I "think" is the setup]

Salim

 

Thanks, I think you are on to it. Where can I get a wiring diagram and where is the ECU located? Is there additional computers or modules that feed the ECU for door information and if so, where are they located?

 

i have the same issue with my friends 99 rx300. all the doors will turn on the dome light except the driver door. it seems the car does not know when the door is open/closed. and the drivers door light never turns on. if anyone has any input on this let us know. thanks

 

This sounds like an easier one. The most likely suspect is the switch that senses when the driver's door is open.

 

I had an um... occurrence once that caused my passenger door ECU (as in the entire part with the window and door lock switches) to short out. Until I replaced it, the car wouldn't recognize the door being open. Lots of electronics + troubleshooting = fun.

 

^^ Bob is right. This is one of the easier ones.
9/10 times it's the driver side door latch assy.(door ECU)
Part # 69040-48020

 

I had a similar problem on my RX300. The dealer wanted to change one of the latches. But before I had the work done. I looked around the internet. And found you can clean the door contacts. So I just sprayed the hell out of all the door latches with WD-40.

Fixed the problem.

 

where is the switch that senses the door open? is it the whole door latch assembly?

 

Yes.

Salim