Hi guys, it's been a while since i've posted on here, life has taken me to a pretty rough place the last few years. I'm a single father now, and I've been on disability for the past two years with no sign of that changing any time soon. My kid and me just moved to a newer area of town in a basement suite so we could get out of a really bad situation, and it's left me with basically no money, and now my car broke down. I have an electronic engineering diploma, so I do have quite a solid understanding of electical systems and how to troubleshoot and diagnose as well as repair them, but looking at the wiring diagrams for this car, I just can't understand what's going on with them. they seem like they really aren't giving the full picture at all.

Basically I went to start the car a couple of weeks ago, and it wouldn't start. No crank, but dash lights and dials and such came on. After some troubleshooting, I found that the starter relay was not getting a start signal, and thus the starter wouldn't crank. I followed that back and found that the 60A E/G-B fusible link was blown. I couldn't think of any reason why, as the only work i had done on the car recently was changing the brake pads on the front, and cleaning some mud out from the bottom side of the engine block on the passenger side, as well as putting some sheet metal screws into the fender (checking for wires on the other side first, of course) to hold the wheel well liner in place better as it was flapping inthe wind. I figured maybe I had simply touched something by accident when i was clearing the dried on mud out, so I bypassed the link with a 60A fuse on a wire, just to see what would happen, and this allowed the engine to fire up and I had no issues. I drove it for the next week or so with no issues, and then a couple of days ago on the way home, the car suddenly went into limp mode just as I went to leave a stop light. I limped the rest of the way home (it was only about 2km), and after shutting the car off in the back of the house, it wouldn't fire up and had similar symptoms to the issue a week ago. Opened the hood and sure enough, the 60A E/G-B fusible link was blown again. So I pulled the battery out, and out of curiosity I measured the resistance between the battery terminals, just to see what it would show, and when I bypass the fusible link that is blown, it reads 0.1 ohms, so basically a dead short. Without the bypassed fusible link, it starts at a low resistance and builds up, suggesting that the meter is slowly charging some capacitors, which makes sense I guess?

So far I've followed the wiring diagrams and found that E/G-B supplies power to the #2 Relay and Junction box on the left side of the engine bay (from the drivers seat), but when i pull the various fuses, the resistance stays at 0.1 ohms with the link bypassed. To me, this suggests that the main wire leading from the fusible link to the junction box must somehow have shorted out somewhere?? does this sound accurate? and if so, where the heck is this wire routed??

looking through the diagrams, I can see this wire should be coming in on connector 2D, which is shown on the Fuse Block diagram page for RB/JB #2 on Unit C. But where the hell is connector 2D? And looking at this diagram, it looks like a whole bunch of connectors are missing from it. Looking down from the top, everything that is in the general area of Unit C isn't shown on this diagram. Or is this diagram showing the bottom of the RB/JB #2?

Please help. I'm desperate. I have a super important doctors appointment to get to tomorrow morning, and I haven't been able to get groceries for a few days now, and we're really starting to get into a bad situation. I'm honestly at a loss for what to do. Any help or advice at all would be super appreciated. I am willing to share my phone number privately if anyone thinks they could help me, or if you want to post up here, please do. I would be grateful for any advice at all.

thanks in advance.

 

Take a look at this. Any chance you have a power tilt steering column?
I'd be suspect of the steering lock system as it's seems to be fed by the 60A fuse. Sounds like you're mostly on the right path as for thinking it's the wire itself after the fuse and something happened to it compromising its integrity.

As for the battery leads, there are so many small paths to ground, I have never measured it, but can imagine it shows low ohms based on the giant spark thrown when connected.

I would place a 12V incandescent test lamp on the downside of the 60A fuse so, one side on +12V, the other the 60A leg gets powered by the bulb. Now start unplugging fuses in the branch below. With all fuses out, that leaves the wire itself.

Last question, the front controller does all outward lighting, has the car ever been wrecked causing significant front end repairs? That would be my next path.

 

just to clarify what you mean about the test lamp, do you mean i would install the battery as normal, or simply connect up JUST the 12 volt post to one side of the test lamp, and hte other side of the test lamp would go directly to the downstream side of E/G-B fusible link? I'm super overwhelmed with this right now, and when I get stressed out like this my brain basically stops working right (i'm autistic..fun times). What's the purpose of doing this? Is the idea that the light will be on (because of the short) until I either pull out the fuse for the component that has the short, or until I find the short in the wire and disconnect the short from ground? If that's the idea (which makes sense to me right now), then would I not also get the same effect by simply putting a multimeter on the downstream side of the fusible link, and the other side of it to ground, measuring the resistance to ground on that leg only, and then going step by step through each leg that is supplied by this fusible link?

to answer your questions, yes, i do have a power tilt steering column. in fact, now that you mention it, a few weeks ago I did notice that my left side shift paddle stopped working. I wonder if the two things are related now.

and no, the car has never been in a collision. I did notice a connector that leads to nowhere that's dangling inside the bumper down by the drivers fog light. i assume this is for some equipment that is optional and isn't installed on my car - i wonder if it is causing an issue. though i kind of doubt that's it as the wires are small gauge and it didn't look like it was damaged at all.

one thing that i'm not understanding about the diagram you posted is why only some of the components show wires leading away from them, and others do not. for example the steering wheel lock fuse line ends at junction box 2, whereas the front control-b line continues on, I assume to the fuses for the horn and the headlamp based on other diagrams i looked at?

looking at this diagram:
https://charm.li/Lexus/2007/IS%20250...on%20Diagrams/

I feel like it is possible that the wire with the issue is the W-L colored wire leading from the E/G-B fusible link to RB/JB #2, but I don't know where this wire is routed. I guess the only way to know for sure is to literally pull the fuse box out and trace the wire from there, but I guess I was hoping I could find out the route it takes so that I could try to inspect it first.

is my thinking correct when i am thinking if I pull the TEL, ALT-S, ETCS, A/F, STR LOCK, and FR CTRL-B fuses, then I will have fully isolated the wire leading from E/G-B fusible link, and thus if I still have low resistance to ground from the downstream side of the fusible link, I will have isolated my problem to that W-L colored wire?
thanks very much for the help.

 

Hopefully I capture most of this. Meters are great for measuring voltage and resistance, but they impose zero load. A test with one end on +12V and the other into a load will light a test. No load, no light where a meter only need micro amps to show voltage. My path would be this, connect battery as normal leaving fuse out. Now start pulling fuses and in the ideal world, you pluck the right one and the light goes out. But that won't explain a 25A fuse killing a 60A fuse so I fear something worse has happened. Unless, someone installed a big fuse downstream? Has this been verified? Toyota and Lexus did have a wire failure on auto tilt steering columns but most of the time it took out CANH or CANL data wires for some reason. What is your source for schematics? It should have chart for locations of grounds, hot, junction blocks and all that. I have accounts on www.alldatdiy.com if I get time, I may try look that over but mine is only for 2013 350 so I may not see the same thing. You are on the right path. Also as you test, try to use a 40A fuse vs 60 to minimize damage.

Edit adding other half of chart.
Tried to add. It hates me.

 

There is more to first picture adding additional loads to 60A fuse. Does this show up on your schematic?

 

thanks for the replies.

so just to answer your questions and comments:

- totally understood re the meter imposing zero load. what i'm struggling to understand is what benefit will putting a test light across the blown fuse, in place of the blown fuse (i.e. don't replace the fuse, instead jump across it's contacts with a test light, such that the test light will pass current like the fuse would have done if it were not blown). this is what you're suggesting, yes? if so, then if there is a short downstream of the fuse, the light will be lit as long as there is voltage being supplied to the upstream side of it (since the downstream side of it would be at 0 volts potential, due to the short). once the correct downstream fuse is pulled (whichever one the short is on, assuming the short is downstream of one of those downstream fuses), this will break the short to ground, thus the test light should go out. but a few questions there - if the other circuits that are supplied through this main fuse draw sufficient current, would they not also light the test light? or would the test light drop voltage to the point that the circuits would not function, thus the current flow wouldn't be sufficient to light the test light. also, if my understanding of your suggested setup is correct, then i would assume that i would get a similar result by simply putting an ohm meter with one lead on the downstream side of the blown fuse, and the other side on a ground point, and then i could simply pull downstream fuses, and when i pull the correct one, the ohm meter should go from 0.1 ohms (basically a short to ground) and would go up to some value (don't know what value it would end up at, since i don't know the circuit resistance of all other circuits, but rest assured it should be much more than 0.1 ohms, since if it was that low, then the current draw would always be very high). my reason for asking this is that i don't have a 12v test light handy anymore as mine got run over by my old roommate, and i don't have another vehicle so i can't easily go out and buy tools.

re a big fuse downstream, no there is no big fuse downstream of the blown 60A fuse. everything is factory as far as i can tell.

your point about how it could be possible for the 60A fuse to blow but not the downstream fuses which all have lower ratings is, to me, exactly why i actually do not suspect my issue to be located on any of the circuits that are downstream of the smaller fuses. if there was a short on any of them, their specific fuse would blow, and the fusible link would be fine, as this is what the purpose of having those smaller fuses is. they are intended to protect against over current draw in the event of a short downstream of them, and to also protect against the larger (and more expensive) fusible link from blowing due to a fault that is on one of the smaller individual circuits.

my understanding of the purpose of the fusible links is that they are there to protect in the event that there is a fault on one of the larger supply lines that go from the fusible links to the various downstream circuits which are all individually protected by their own fuses, located in various junction boxes around the vehicle. so the only logical reason for a fusible link to go, but not any downstream fuses, is if there is a short that is located in between the fusible link that blows and the downstream fuses from it.

actually, now that i've thought this through a bit more, on a clear mind, and talked it through here with you, i'm realizing that the only logical explanation for this fusible link to be blowing is a fault in the wire that goes from the fusible link to the relay/junction box #2. it is the only wire that is between the fusible link and the other, smaller, fuses, so if the fault was downstream of the smaller fuses, they would inherently HAVE to blow before (or worst case, with) the fusible link.

i just couldn't picture a situation occurring where a circuit protected by a <25A fuse has a fault to ground on it, but where sufficient current to cause the 60A fusible link to blow would be able to be drawn through the <25A fuse without blowing it. these smaller fuses should blow faster, and at a lower current, than the 60A fusible link.

thus, the W-L colored wire leading from relay/junction box #1 to relay/junction box #2, which goes from the 60A E/G-B fusible link to the ALT-S, ETCS, A/F, and STR-Lock, and the Front CTRL-B circuits, is, to me, the only logical answer for where my fault lies. would you tend to agree here? or is there something that i am missing?

 

as for the diagrams, i am getting all of my diagrams from here:

https://charm.li/Lexus/2007/IS%20250...%284GR-FSE%29/

which is charm.li

it appears that these are all factory diagrams, as some of them do match the diagrams you have posted.

what i'm struggling with is understanding where exactly the connectors are on the relay/junction box #2. if you go to the Fuse Block diagram pages, and look at the diagram for

Engine Room R/B No.2, J/B No.2 - Engine Compartment Left

you can see the box shown, and on it there is Unit C at the top, unit A on the lower left, and Unit B on the lower right. After thinking about this, I believe this drawing is actually looking up from the bottom of the box, as the connectors shown as being on Unit B are actually on the left side of the box when viewed from the top, but they are plugged in from the bottom of the module that is slotted into the junction box. additionally, the connectors that are shown on Unit A and Unit C do not match up at all with any of the connectors that go in from the top. i think this is what has been confusing me.

based on the Power Distribution Diagrams, Power Source Part 1, and based on the diagrams that you posted, it appears that the 60A E/G-B fusible link (located in Junction Box #1 by the battery) ONLY supplies power to the 7.5A ALT-S, 10A ETCS, 15A A/F, 25A STR-LOCK, and 25A FR CTRL-B circuits downstream, all of which are protected by their own individual fuses, none of which are rated higher than 25A. This should absolutely support my theory that the fault MUST lie in the connection between the 60A E/G-B fusible link and Junction Box #2 (located by the washer fluid reservoir and the main ECU under the hood (near the drivers side headlamp assembly basically). A fault anywhere else in the system should be blowing the smaller fuses, and likely not the fusible link at all.

So I think what my next step might be is to pull all of the fuses mentioned above (the smaller ones, 25A and less), then measure resistance from the downstream side of the 60A E/G-B fusible link to ground. If that resistance is still 0.1 ohms or so, then i cannot see any possible way that the fault would lie anywhere other than the wire between these two junction boxes.

Sound logical?

 

PROGRESS!!!!

So i pulled apart the J/B No 1, the one with the fusible link in it, and i disconnected the wire from E/G-B fusible link (white with blue line). Then I put the ground lead from my multimeter on the negative cable (battery removed of course), and clamped my positive lead from my multimeter onto the eyelet connector of the E/G-B wire. Since the junction box was disassembled, this gave me some play in the bundle of wires, and I removed the electrical tape and split loom wiring harness sheath from the bundle of wires coming out of the bottom passenger side of this junction box (which the E/G-B wire is a part of). Then I set my meter on auto ranging ohms, and started to wiggle the wire back and forth, pushing in and out, and before I moved the wire, it was showing approx 500kOhms or so. When i moved it in one particular direction though, the resistance plummeted down to under 10 ohms, and even hit 0.1 ohms a few times. But it wasn't very easy to reproduce exactly. So I worked my way down the bundle of wires towards the point where it splits off, with some of the wires going through the firewall, and some of them going down under the battery tray and under the computer box th ing that is under the battery tray.

there is a section of the bundle of wires a few inches away from the firewall where, when i pinch it in a specific direction, or when i press gently downish and a little towards the drivers side of the car, i can very easily reproduce the 0.1 ohm condition. i'm not totally sure though that this wire actually GOES into the firewall, or if by doing this I am simply flexing the rest of the bundle, but the net effect is the same - it causes this white with blue stripe wire to short out to ground!

now here's my thought - maybe you can correct me if i'm looking at this wrong, but when i look at all of the wiring diagrams, it seems pretty clear to me that this wire goes directly from E/G-B 60A fusible link in J/B #1, over to J/B #2 by the drivers headlamp assembly, supplying power to the ALT-S, ETCS, A/F, STR LOCK, and FR CTRL-B fuses. I cannot see ANY other places where this wire is connected to. If I am correct here, then I would be able to simply disconnect both ends of the wire, run a new wire (I wouldn't even need to follow the original route, just simply need to make sure it is safely routed from one J/B to the other), and connect it up at both ends. Since the original wire would just be dead, I wouldn't need to worry about removing it from the car.

My only concern with doing this is that then I would still be risking other wires in that same area getting damaged by whatever damaged this wire. Not sure how likely that is to happen, but I think it would def be a risk. But I don't know if I have it in me to start pulling the whole dash apart on the passenger side, along with pulling apart the wire bundle on the engine side of the firewall.

Any suggestions here? How hard is it to get enough of the dash out that i could access the area where the wires come through the firewall on the upper far passenger side?

 

I don't know if this will help but, lots of times here we see these kind of wire problems. It's the result is a Rodent got up there and chewed on some wires. Did you check to see if there was any evidence of a Rodent anywhere?

 

I don't have time for a detailed response, but glad you found the location of short!

I know you have limited options for tools but plan on purchasing a crimp tool, bare crimps (butt connectors) and shrink tube for a proper repair if the wires core is damaged.

I'll make a list. Just make sure whatever is done doesn't overheat and cause a fire. i.e. bad connection or too sma of wire. These conditions are actually worse than a short as they won't open the fuse.

 

oh i've def got a fair number of basic tools. crimper, eyelets, etc. i don't personally use butt connectors - when i was in college i took some electronics classes, and we were taught the j-hook method to solder join two wires, and i use that with heatshrink tubing over top to ensure the joint is protected. I've just seen too many cases where crimped connections can fail, if they aren't also soldered, and butt connections are essentially impossible to solder properly and still maintain an insulated connection. but by making a j-hook on each wire, slip heatshrink over one wire, hook the two j-hooks together and then pinch the ends together so they are tight together, and solder that joint well, the resistance of the joint is lower than a crimp-only connection, and it isn't nearly as prone to heating during higher current draws.

as for a rodent infestation, no, there is absolutely no evidence of rodents damaging wires at all. i'm honestly baffled as to how this wire could have become damaged.

 

so i've managed to get the junction box #1 (by the battery) apart fully, but I cannot, for the life of me, figure out how to get the junction box #2 (by the drivers headlight) apart. and i can't find where this E/G-B supply wire comes into this junction box. it doesn't come in from the top side I am quite confident of, so in order to fix this issue, I need to find where the heck this wire goes.

does anyone know where it is routed from the junction box #1? or even a general idea of where it goes? does it actually go into the firewall and across the firewall or something? i can't imagine it would - i don't see why that would be done.

can anyone help me figure out how to get this damn junction box out? do i need to pull the ECU box out first?

 

PROBLEM SOLVED AND ISSUE FIXED!!!!

It was definitely a short in the E/G-B to JB #2 wire, which is white with a blue stripe. It is routed from JB #1 by the battery, out the passenger side of the box along with the bundle of other wires, and then it goes down under the battery and the computer that is mounted down there, along the firewall right to the drivers side fender, under the lip that hangs out under the edge of the hood, and follows the hood line until it gets to the JB #2, where it takes a turn down to the front bottom of the box and enters there. I was able to open the wiring harness "box" along the fender, dig out the wire from the bottom of the bundle of wires, and this is where I made my cut. Then I spliced in my replacement wire, and ran it in a similar route, though a little higher on the firewall as I couldn't reach far enough down to follow the original routing. I did modify the JB #1 a little, to give myself a way to access the bolt that secures this wire to the fusible link module, just in case something was done wrong here and I needed to replace it again (I didn't want to pull apart the JB again if this happened - it was just too big of a pain in the ***!). Once everything was hooked back up again, the car fired right up on the second start, as expected. SOOO HAPPY!!!!!! I got my car back!!!!

Thanks for the help and advice, and for talking through this with me!

 

Congrats on your persistence. This would have cost you a small fortune at a shop and I doubt they would have found the problem.

 

Hi Guys , Need some help.

I have started the car with no issues , then got a fault code P0035 and P0058 - B1S2 and B1S1 heater sensor low voltage .
After investigating I found that the catalyst convertor post heater wire was damaged, and I repaired the wiring.

when I try to start the vehicle to clear codes the vehicle doesn't start.
When depressing the brakes start button and all ignition lights come on but no power from push button to starter solenoid, I have check battery voltage 12,8vDC, Starter solenoid wire is all fine and connected, check the starter relay and is fine. , when bridging the relay B+ and ground with ignition on, the vehicle is starting and switch off on the start button,
But when depressing the break with car in P-Position there is no power to the start relay to energize for the power from the battery to the starter motor solenoid .
there is 12v on the main B+ on the relay wire.
I checked all fuses and all are fine,

What could cause the starter relay not to get a current to energize the coil to supply starter with battery voltage.
any assistance please