Dome light issues 04 prerunner.

So I have seen a few other posts regarding this issue, and it doesn’t seem like anyone else got the answers they needed so I figured I’d make my own post. I have a 2004 Tacoma prerunner. A few years back I started running an LED in the dome light with zero issues until now. The dome light recently stopped working in the door position, but works when switched on. However, in the door position, when the vehicle is unlocked with the key fob, the light comes on. So it’s only the door switches that are not working. Checked the door switches with a multimeter, they all work fine. Super confused, because as far as I can tell from the wiring diagram, both the ON and DOOR positions get power from the same wire, so that should be fine. And unless I’m mistaken, I haven’t found a separate ground wire shown for the key fob to use for the DOOR position, so I’m at a loss at this point how the DOOR position ground could have a fault. Still haven’t done a continuity check from the switch back to the body control module yet, will have to wait till after work, but if that shows no faults I’m not sure what else to check. Anybody who’s had and fixed this issue who can provide some insight as to what I’m missing would be greatly appreciated.

 

I'd swap a halogen bulb in it and see if it works. A LED bulb (without a resistor) never worked in my 01 double cab, made the BCM go crazy.

 

Apologies, forgot to clarify that I did swap in a halogen with no success. Also the LED worked for years, and the issue only came up when I tried to swap a brand new bulb, same brand.

 

So i'ts been almost a month and I still haven't resolved this issue. Wiring all rings out good with a multimeter, the dome light switch is good, it even turns on in the door position when the key fob is used (via the TVIP ECU, it shares the black and white wire that goes to the body ECU for the door switches) to unlock the vehicle, which tells me that everything from the fuse junction block all the way to the body ECU is good, and my problem lies at the body ECU, or possibly but very unlikely all four door switches, which appear to be working with a multimeter. I have tried reseting it by disconnecting the battery and waiting 15 minutes with no luck. Anyone else reach this point and find a solution other than a new body ECU? Also, would a dealership be able to run a diagnostic on the ECU to detect an internal fault with the dome light door switch circuit? I don't know what else it could be, and at this point, I've pretty much resigned to either not having a door activated dome light, or deleting the wire that goes into the ECU and taking it directly to the door switches. Y'alls input is greatly appreciated.

 

As the switch contacts can get dirty have you tried cleaning them.

I have them test fine with the meter yet still not close until cleaned.

 

The switch has to be good, the light turns on when in the DOOR position if unlocked with the key fob. As per the wiring diagram, this means it is grounding via the black and white wire that runs off of the DOOR side of the dome switch, and splits going to both the body ECU, and the TVIP ECU. In the case of being unlocked by the key fob, it’s getting its ground from the TVIP ECU. For whatever reason, it’s not getting a ground from the body ECU/door switches.

 

My 98 4Runner had similar issues with the overhead lights. Did all the electrical checks... replaceing all the door swithes fixed the problem for me.

 

Okay, thought I had checked those but maybe I missed something. Thanks for the input.

 

Has anybody back probed the connector for the door switches where it connects to the body ECU, and if so, does anyone know if you are supposed to get 12 volts there? Or is it a lower voltage that just passes the signal to the ECU to ground it elsewhere?

 

https://charm.li/Toyota Truck/2004/Tacoma 2WD V6-3.4L (5VZ-FE)/Repair and Diagnosis/
look under "body and frame /
body control" tab for diag info.

 

Appreciate that thank you. Is that from the service manual, or the wiring manual? Also I am assuming that those pin out values are with the everything connected and back probing the connector?

 

Your door switches close completing the ground when the door opens .

I have replaced many left door switches they do wear out.

In my own vehicles I just remove the bulbs and never use the lights. They just never light what I need to see.

 

I'd back prob the ECU door switch pins.
Open and close the doors and see if the ECU is being pulled to ground.
If not, there is issues in the wiring to the ECU.
If not, then the ECU isn't working "right".

 

Will check with a multimeter tomorrow. If it is pulling to ground, (meaning I'm reading ~12v correct?) then I guess I missed something with the wiring/switches, and my course of action is pretty straight forward. If not, and the body ECU is indeed bad, what are my options? Is there anybody that repairs them? Or do I have to get a new one from the dealership or a scrap yard?

 

Typically, in these case. The wire will voltage on it when the door is closed (Switch open / Door Closed).
When the door opens, the switch closes, and the wire at the ECU should go to 0v-1v.

Basically, when the ECU see a ground connection, it supplies a ground to the light.

 

Okay, didn’t know that. So the door switches do not complete the circuit, they merely send a signal to the ECU which then grounds it from the white and black wire shown bottom right of the diagram?

 

Door switch wires back probed at the connector (1L) read 0 volts with doors open, and .3-.4 volts doors closed.

 

0v is right with door(s) open.

BUT...... .3/.5v is not right.
It should be about 5v-5.5v

So lets clear things up.

1. When the switch is set to ON, the ground is supplied by one of the screws for the switch.
2. When the switch is set to DOOR, the ground is supplied by the Body ECU @ the 1H Connector - Pin #9.
3. It passes through the IG1 Connector at pin #3 before it gets to the body ECU.

So, Have we checked the ground at the BODY ECU 1H Pin #9 or the IG1 pin #3?

Also, still confused at the .3/.5v as that is low.
But we need to see if the ECU is even providing a ground.

Obviously, you'll want to have to have the doors open when testing.
You might even supply your own ground to the 1L Door Switch pin just make good and sure the ECU has a good ground at the pin.

 

Will check when I get home. Thank you very much for the help. Electronics is not my strong suit, so any and all advice I can get is greatly appreciated.

 

On a brighter note, just got new tires put on, and they look great! Pics coming shortly…