idosubaru Posted August 9, 2017 Share Posted August 9, 2017 (edited) Narrowed down XT6 no spark condition: ECU supplies power to the CAS and it shows 0.5V at both ends (at CAS harness and at ECU pin for CAS power) FSM says it should be 7V or higher. It seems the ECU also has low power so I'm tracking that down now. Not sure why the FSM didn't specify to look there or I missed it. The check engine light doesn't work - although ECU pin shows 12 volts so I assume the bulb is blown? The ECU LED won't light up either so I'm confused but the FSM doesn't spell anything out for that LED. Edited August 9, 2017 by idosubaru Quote Link to comment Share on other sites More sharing options...
Gloyale Posted August 9, 2017 Share Posted August 9, 2017 The check engine light doesn't work - although ECU pin shows 12 volts so I assume the bulb is blown? The ECU LED won't light up either so I'm confused but the FSM doesn't spell anything out for that LED. Backwards. ECU grounds the that pin to illuminate light. So if your are seeing 12v, you are seeing the power through the unlit bulb and no ground on the ECU side to light it. If the light was on you'd get zero volts or full ground. I would check all the ECU grounds for continuity to body, and check the intake ground bolt. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 9, 2017 Author Share Posted August 9, 2017 Copy - ECU grounds had continuity (I'll check that I got them all, I think I tested 6). Should I check resistance of them if that's even possible? The ECU power supply voltage is low or nonexistent. The engine fuse in the cabin fuse box blows at the exact same time the ignition relay clicks. I repeated that multiple times. That tiny screw on the back of the ignition was very loose. I tightened it but still same issues and the back of the ignition still seems to have some play. . I'm unsure how to test the ignition and haven't seen it in the FSM. I'll dig some more. Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 9, 2017 Share Posted August 9, 2017 Unplug the ignition relay and see if the fuse still blows. If not, you know it is after the relay and you can stop looking at the ignition switch. You can also check for a dead short to ground with an ohmmeter at the relay. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 With the ignition relay removed the cabin engine ignition fuse doesn't blow. I don't understand what that means. If I disconnected the battery or fusible link it would also stop blowing the fuse but I see it's in series I just don't unserstand how that guarantees it's up or downstream. You're sure this rules out the ignition switch, because I don't fully get that? So we are back to grounds somewhere like you guys have stated. How does a ground cause over current? High resistance from a poor contact? Can I test resistance somehow between that fuse and ....somewhere else? Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 No, you can stop looking at grounds for now. You have a dead short downstream of the ign relay. Get the wiring diagram out and start following that circuit. If you don't see or think of anything obvious, like where someone has messed with the wiring before, installing accessories or whatever, use the split-half method. That means, going halfway through the circuit to the nearest means of disconnect, and check both sides for continuity to ground. When you find which half is shorted, go halfway in that section and do the same. I can't think of anything obvious at the moment for you to go right to, but I'll edit if I do. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 Yep I'm going to study the FSM tonight. Dead short - so that means a power wire is directly shorted to ground somewhere? Downstream - what does that mean? Previous owner has an aftermarket starting relay or something installed - I know nothing about it. Probably a good chance that's the problem? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 Thanks guys. Can you help me unserstand this? Here's the aftermarket relay (I assume) - right above the coil. Maybe it simply failed - but if it's only for the starter it shouldn't effect the ECU and driving? Far right wire: positive battery terminal Far left wire: starter Middle right wire - it's spliced into some unidentified stock wire that snakes back under the windshield cowl. Where does that wire likely lead - ignition? I'll check continuity tomorrow. What I don't understand is why it only has three connections? It's been like this for 10,000 miles ive owned it. It also has aftermarket Hella lights installed Im going to see if I can disconnect those as a test. Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 Yes, dead short if the fuse blows instantly. Downstream, means after the relay. So everything from the battery to that point can be ruled out. Aftermarket anything is the best place to start! Factory Subaru wiring very, very rarely develops this kind of problem on it's own. 99 percent of the time, it's from stereo installation, fog lights, remote starter, trailer plug, etc. Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 Thanks guys. Can you help me unserstand this? Here's the aftermarket relay (I assume) - right above the coil. Maybe it simply failed - but if it's only for the starter it shouldn't effect the ECU and driving? Far right wire: positive battery terminal Far left wire: starter Middle right wire - it's spliced into some unidentified stock wire that snakes back under the windshield cowl. Where does that wire likely lead - ignition? I'll check continuity tomorrow. What I don't understand is why it only has three connections? It's been like this for 10,000 miles ive owned it. It also has aftermarket Hella lights installed Im going to see if I can disconnect those as a test. That thing is wired to the starter solenoid??? WOW!!!! That's super overkill for starter circuit bypass! But sorry, no, not the cause of the problem you're having now... we'll deal with that later. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 If I want to check the purge control solenoid circuit for a dead short - how do o do that? Check Continuity and resistance from another access point/sensor? One side of the fuse that keeps blowing leads to the pin on the ECU labeled "Ignition Switch Signal". Along the way these components T-off of that line: Fuel pump relay Diode Purge control solenoid By pass air control Check connector Ignition coil So one (or more) of those items has a bad circuit? The other side of the fuse goes to the ignition switch. Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 (edited) You can check any component or section of wiring with an ohmmeter. With one lead of the meter grounded (double check that by testing to a known good ground source) and the other lead on the wire or terminal of the circuit you are testing. You'll be looking for really low resistance to ground, like 10 ohms or less. You can also do this somewhat more crudely with a test light, by clipping the normally grounded end to a power source, then probing with the tip. If it lights up really bright like it does when you touch it to ground, you have found the path to your short. You can do it even more crudely, if you have plenty of fuses, by just unplugging things till it stops blowing them... but I would advise the first two methods. Just keep unplugging and testing both sides where you unplug to narrow it down. Edited August 10, 2017 by Subaru Scott Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 I'm going to guess to maybe start with the fuel pump and the ign coil. Also, have you ever pulled out your passenger seat to address the rotted injector wire junctions under the carpet there? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 You're the bomb, big help I'll try that. Just checking resistance, sounds odd just checking wire resistance but I've done that with parts Never pulled the seats Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 You're actually checking continuity to ground, not resistance in particular as a measurement. The ohmmeter is the preferred tool which shows resistance in a circuit or component. And when it shows super-low resistance to ground, on a power circuit, it means the wire, or component at the other end, is connecting to ground before it goes through the load of the component. If it shows high resistance, it means the circuit is going through the load as it should, and then to ground. There are conditions, of course, that can give you false readings sometimes, but this is how we start. You can use a test light too, as I said (my first tool of choice). If it glows really bright, you have low resistance/good continuity. If it's dim, you still have continuity, but higher resistance. The issue under the seat is pretty common with XTs, but the XT6 may be completely different. Water that leaks in from the side window, the cowl, the windshield, y'know, just sits in the floorboard and rots out the injector wire junctions where they split there. It's pretty well insulated there, so not much chance of a short to ground. Some of the injectors just lose power. But if someone has half-rump roast repaired them before, and removed most, or all of the insulation, that could be an issue. Quote Link to comment Share on other sites More sharing options...
skishop69 Posted August 10, 2017 Share Posted August 10, 2017 Continuity check to ground for shorts is great, but continuity checks on circuits (wires) end to end mean nothing. You can have low resistance on a wire and have your correct voltage and still have little to no current. Say you have 20 strands inside the wire and over the years, do to vibrations and movement, 19 of the strands break inside the insulation. It happens. I see it at least a couple times a month at work. Now you have one strand left that will show good voltage and low resistance but it will not be able to supply the necessary current to run the load. If you suspect a wiring issue on a circuit, you should do a loaded voltage drop test or load test the circuit. I mention this in regards to your voltage issues at the ECU. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 Got it. Thanks, makes sense. Except loaded tests, i don't know what that is. I have is a basic multimeter - amps ohms volts continuity. Here's my current (haha) question: So the ECU wire from that fuse (#11) that keeps blowing - I can literally check to see if that has continuity to ground? So I'll test the power feed for each of items connected to that same wire and one should have continuity since the fuse is blowing every time - so clearly something on that line has a short? Is that correct? I've never done that so it sounds crazy - I'll literally get a continuity confirmation from a hot wire to ground? something tells me I'll strike out probably because I've never done it but I'll do that first. Tell me if this sounds right - since the fuse blows every time, the ECU has to be zero volts so that's more of a symptom than a cause - at least until I narrow this thing down? Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 Yep, start right at the output of the ignition relay, you should find continuity to ground with very low resistance (ohms), like 10 or less. Then, start eliminating portions of the circuit and components by unplugging, till you show no continuity to ground, or continuity with high resistance as is normal when going through a load to ground instead of directly to ground. Start with some of the easy things known to short out on their own, fuel pump, ign coil. Then the ECU, not likely, but it could happen. Once you have eliminated the components from the circuit, you will then be looking for a place where the wiring has been damaged or rubbing against the body. Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 10, 2017 Share Posted August 10, 2017 To be specific about your starting point, you'll be checking one of the two big wires at the ign relay. One should show battery voltage all the time, and the other will be your output, or load wire. You can even leave the meter connected there while you unplug components and sections of the harness. I just suggest the split-half technique because it narrows things down faster. Quote Link to comment Share on other sites More sharing options...
skishop69 Posted August 10, 2017 Share Posted August 10, 2017 To be specific about your starting point, you'll be checking one of the two big wires at the ign relay. One should show battery voltage all the time, and the other will be your output, or load wire. You can even leave the meter connected there while you unplug components and sections of the harness. I just suggest the split-half technique because it narrows things down faster. +1 A loaded voltage drop test is simple and done with a generic meter. Set the meter to volts. Power the circuit on and place the positive lead on one end of the circuit and the negative lead on the other end. It doesn't matter which lead does on which end because you're measuring the voltage drop or differential on that circuit. You want the reading below 0.5v which would mean you're losing less than 0.5v across that wire. Anything above 1.0v is a problem. The reason you want the circuit and device powered up or 'loaded' is that sometimes circuits will only fail when loaded. Straight load testing on the circuit is easier and you can do this with an 1157 or 3057 bulb and socket. wire the two positives for the bulb socket together so you now have one + and one - wire on the socket. Place the wires accordingly on the circuit you wish to test. if the bulb glows bright, they are most likely good. If it glows dim, you have a problem with either the power or the ground circuit. Now you would leave the + attached and take the - directly to ground. If it still glows dim, the problem is on the + circuit. If it glows bright, the problem is on the - circuit. Technically, you should use a small halogen bulb for the build so there is a larger draw, but I have ran across a few scenarios where the draw is too much and things go pop, snap, fizzle so I use the 3057. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 Ignition relay lead: 740 Ohms (car off), 770 Ohms (car on) same wire on the fuel pump relay only registers on the 20,000 scale. By Ohms law 720 Ohms would only produce a fraction of an amp, not enough to blow fuses so I'm confused? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 10, 2017 Author Share Posted August 10, 2017 (edited) Power the circuit on and How do you do that if the fuse blows the instant you turn it on? If I ran a power wire to power it around the fuse it seems like it'll overheat? Edited August 10, 2017 by idosubaru Quote Link to comment Share on other sites More sharing options...
Subaru Scott Posted August 11, 2017 Share Posted August 11, 2017 740 ohms is definitely not a short. Are you sure you're on the right wire? It will be the one of the two large wires that do NOT show 12 volts. Could you put up, or send a link to your schematic? Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 11, 2017 Author Share Posted August 11, 2017 oh man you're confused....Ive got no hope for my daily driver xt6!! Haha. I tested it from the fuse (the one that keeps blowing) and it showed the exact same numbers as from the relay. But the wire is larger like the red one and white/black just like the FSM says. The other two pins in the relay don't show anything abnormal, I think they showed nothing or didn't register until I changed the scale to 20,000. I don't get it - it's got 12 volts on one side and 740 ohms on the other - how can it blow? I inserted another fuse after testing and sure enough - pops immediately when the ignition relay clicks. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted August 11, 2017 Author Share Posted August 11, 2017 Schematic is huge and convoluted. I'll look for a smaller one, may have to post it tomorrow morning. Quote Link to comment Share on other sites More sharing options...
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