The dome light fuse in my 2006 Sienna blows every few days. Been to 3 mechanics on 5 occasions, including a dealer. Still a mystery. And I’m so tired of getting into my dark car, especially late at night. Here are the answers to the questions the mechanics all ask me - I’m the original owner, never been in an accident, no after-market anything (radio/alarm/etc.). Unfortunately, it’s not the visor vanity lights - that’s been checked, including disconnecting them. If you could offer any ideas I would sure appreciate it.
Which light? Front or rear? I would suspect a short around the door switches.
Is the wrong amp fuse being used each time? There should be a diagram near the fuse box or on the back of the cover.
The big problem for both you and the mechanics is not knowing how much time it will take to discover the cause. There is no way to estimate the cost. I once spent many hours spread over several days diagnosing something similar. It out to be a pinched wire, but it was my boss’s car and he owned the dealership. I have no advice for choosing a mechanic, but would recommend you pick one and stick with him. Each time you take it to someone new they will waste time duplicating the efforts of the previous mechanics.
Like MTravler stated, the trouble could be due to a pinched wire somewhere in the roof liner or in the pillar, possibly due to a screw. I assume the fuse ties to number of other areas that could cause the trouble but if the dome light is the prime suspect then it may be take less service time to just run a new wire between the fuse and the dome light and bypass the problem.
You need an auto electric person rather than a mechanic. I guess I wouldn’t fault the general mechanics but a dealer should have at least one person who knows how to use a short finder and actually own one of the tools. It’s a simple tool but very effective. It replaces the fuse with an automatically resettable breaker and uses a compass to probe for the short. A number of tool companies sell a version but you could make one easily enough.
A short finder will only find a short while it is shorting out. If the short occurs only when the vehicle is bounced or when some specific circumstance is occurring the mechanic must duplicate the circumstance or isolate all possible and likely circuits one at a time and return the car to service to see if the problem occurs again. But just for grins and giggles, does the car have a lighted vanity mirror on the passenger side sun visor? If so replace the fuse and swing, flip and twist the visor to see if the fuse blows.
Following Rod Knox suggestion about the lighted vanity mirror, does your Sienna have a self-dimming rear view mirror? I don’t kmow if it is on the same circuit, but you might try disconnected the mirror if it has this self dimming feature and see what happens.
I would look at the wires that go from the body to the drivers door. that would be my first choice for a probable short.
Dose this car have pin switches in the door jam? I would check those or whatever type of switch is used. This is the most common place for a short.
Looking at some data for the dome light circuit power it shows the power going to a lot more things than just the dome light so my previous suggestion to fix the trouble isn’t real good. The dome light fuse in the panel under the hood ties to a junction point in the dash fuse panel. Connection point C27 of the panel ties fused power to 3 other points in the dash panel, they are P16, R6, and L13. These 3 points tie to a number of places for the door lights, roof lights, and vanity lights. To me, this is the most logical point to start the hunt for the trouble. By removing two of the legs one will be left on line to see if the fuse still blows out. If that works ok after enough time has gone by then add another leg and see if that works ok. If that works ok then by process of elimination the trouble must be on the final leg not connected on line.
P16 ties to the luggage area and left slide door.
R6 ties to the interior lights and vanity lights.
L13 ties to the right slide door and other points.
After the correct leg with the trouble on it has been determined it will be a lot easier to pin down the problem area since a lot of possible areas of trouble will have been eliminated. Like Barkydog suggested, the doors are good suspects since they can stress the wires when they open and close.
One thing you could do is purchase a 10 amp circuit breaker and add some leads on it so it could replace the dome fuse until you find the trouble and fix it. The breaker will reset itself after the intermittent short is removed and you will have lights again. I wouldn’t make that a permanent fix though.
That would seem the most practical and professional way to find the short, Cougar. But it requires a wiring diagram that indicates the location of junctions and a working knowledge of DC wiring plus a few tools that are rare to the DIYer. Most car owners would quickly tire of the effort and find a good shop if they didn’t get lucky and find the problem very quickly.
I hear ya RK. Intermittent troubles like this are a real pain to find. The OP asked for help, so here we are, hopefully with some advice that will help get this trouble fixed. If the owner is determined enough I think he could pin down the trouble himself. Investing in a factory wiring diagram manual would pay for itself in this one case alone. Along with a getting a meter to test with. The investment costs to the owner would be a lot less than shop labor costs would be.
Another thing that could be done is install seperate 5 amp fuses, one for each of the three power legs coming from the dash panel. When the trouble happens again only one leg will go down and the hunt could begin using the service manual as a guide.
It seems that great minds do think alike, Cougar. Your methodology is spot on with what seemed to develop with my struggles to find shorts. I must have had 8 feet of Mitchell wiring manuals when I moved to Alldata and MOD. Electricity is one of those problems that seems to be difficult to nail down for most people. Like music, it just makes sense to some and the rest of us just try to enjoy it. Many door switches ground the dome light circuit so a short in the wire just turns on the light. But so much of the problems that are tossed out here are way beyond the average car owners knowledge and ability. Sometimes they get lucky and one of us sees through the desperate meandering of the troubled OP and hits a home run. A few of them post their appreciation. I win more often here than I would on a slot machine and my losses are much more affordable.
SO I am having ALMOST the same issue. Only my fuse Blows Instantly everytime. I have tried a bunch of things with no luck. Any ideas? Where can I find a wiring diagram. 2015 sienna
Checked all the bulbs Pulled the ceiling center console and unplugged This allowed the fuse to go in without blowing!! Pulled all the bulbs Still good Bought and replaced all interior bulbs Worked for a few hours, then started blowing again.
Don’t know what else to do.
An auto-electric tech would measure the resistance of the bulb circuit when the bulb wasn’t installed. It should measure infinite, but I expect it doesn’t. From there they’d trace the circuit to find out where the short circuit was occurring. Usually it would be in the area of the bulb’s fixture.