Toyota Scion Electrical Problem

3) There is Continuity and Voltage between Battery and Starter.

4) There is no Continuity OR Voltage between Alternator Batt. Terminal and Positive side of Battery.

You can't have both continuity and voltage at the same place unless you're measuring them differently. You should have continuity between the battery and large starter terminal, but no voltage difference between those two points. If you measured the voltage at those two points with the meter negative probe on ground, that would make sense. There's no reason to expect that fat cable to be damaged.

Similarly, there should be continuity between the battery positive terminal and the generator's output terminal. You found none. You should find 0 volts with your meter probes on those two points, but if you measured AT the generator with the meter negative probe on ground, you should find 12 volts. The confusion is did you measure "at" or "between"?

Continuity measurements must be taken in circuits that are not powered up, otherwise you will get some false readings. While measuring the voltage BETWEEN two points can be useful, taking them AT various points with respect to ground is more informative and easier to understand.

Double check the voltage at the generator's output terminal with the meter negative lead on ground. First use the battery's negative post for ground, then verify the reading by using the generator's case as ground. I think from your readings, you're going to find 0 volts there. There are six diodes in the generator. Those are one-way valves for the output current. They let that current flow to the battery, but when it's not running, they block current flow from the battery. By reversing the jumper cables, those diodes were "forward biased", and only the minute resistance in the battery cables limited the current. There is a limit to how much current those diodes can handle and that limit would have been exceeded by many times. Most cars have a very large 80 - 120 amp fuse bolted into the under-hood fuse box which might save the diodes, but when two of them short and allow excessive current, they follow that by burning open so the short is gone. The generator is destroyed, but the short is no longer in the circuit, just as if that wire to the output terminal was unbolted.

If you don't have a large fuse for the generator, there may be a fuse link wire going to it. That is a small section of wire spliced in that is smaller in diameter so it's the weak link in the chain. The insulation is designed to not burn, and it will be a different color than the rest of the wire. You test them by pulling on them. If they're good, they'll act like a wire. If they're open, they'll act like a rubber band. Somewhere between the battery positive cable and the generator output terminal is a break in the circuit.

Many manufacturers use the generator's output terminal as a convenient tie point for the wires feeding other circuits. If yours does that, you might see more than one wire attached there. That would explain the dead starter relay.

Also check the operation of the head lights or dome light. If those don't work either, check for voltage on any of the fuses. The smaller positive wire that is typically bolted to the fuse box may have burned open, or the smaller negative wire bolted to the body may have burned open.

Please read [very carefully] my Case-Contrasted (UPPER) replies within your test. NOT yelling, okay? ADDED THIS WAY FOR CLARITY. Thanks!



You can't have both continuity and voltage at the same place unless you're measuring them differently.
THEY WERE MEASURED DIFFERENTLY: CONTINUITY AND DC VOLTAGE, SEPARATE TESTS.

I THOUGHT I MADE THAT CLEAR, AS LUDICROUS A 'PROCEDURE' AS THIS MAY HAVE APPEARED TO YOU.



You should have continuity between the battery and large starter terminal, but no voltage difference between those two points.
THERE IS NO DIFFERENCE IN VOLTAGE AT THESE TWO POINTS.

CONTINUITY IS: 0.00 (RINGING. IT'S A FLUKE II).

VOLTAGE IS SAME AT BOTH POINTS WITH - TEST TERMINAL TO GROUND/-TERMINAL.

AGAIN, I THOUGHT I MADE THAT CLEAR TOO.



If you measured the voltage at those two points with the meter negative probe on ground, that would make sense. There's no reason to expect that fat cable to be damaged.
AGREED. IT IS NOT DAMAGED, BECAUSE CONTINUITY IS SOLID, WITH RESISTANCE OF 0.00 OHMS.



Similarly, there should be continuity between the battery positive terminal and the generator's output terminal. You found none.
(SIMILARLY? IT'S REFRESHING TO SEE A TECHNICIAN WHO CAN SPELL, AND WRITE. NO PUN!)

CORRECT. THERE SHOULD BE, BUT THERE IS NONE.



You should find 0 volts with your meter probes on those two points, but if you measured AT the generator with the meter negative probe on ground, you should find 12 volts.
THAT'S MY POINT---NO VOLTAGE AT ALL WITH - PROBE TO GROUND! HOWEVER, IF I PUT - PROBE TO + BATTERY TERMINAL I GET THE SAME DC VOLTAGE READING AS IF I WERE CHECKING THE BATTERY.

SOMETHING IS DEFINITELY WRONG HERE.



The confusion is did you measure "at" or "between"?
'AT' (WITH - PROBE TO GROUND/- BATT. TERM.) FOR VOLTAGE: NONE!

'BETWEEN' FOR CONTINUITY: NONE!



Continuity measurements must be taken in circuits that are not powered up, otherwise you will get some false readings.
SOME FALSE READINGS, YES; BUT NEGLIGIBLE FOR PURPOSE OF A 'NO START' PROCEDURE. AGREED?



While measuring the voltage BETWEEN two points can be useful, taking them AT various points with respect to ground is more informative and easier to understand.
AGAIN, AGREED! I'M SURE THAT I FOLLOW YOU.



Double check the voltage at the generator's output terminal with the meter negative lead on ground.
DID THAT. NOTHING!



First use the battery's negative post for ground, then verify the reading by using the generator's case as ground.
ALL GOOD! NO VOLTAGE; CONTINUITY STRONG.



I think from your readings, you're going to find 0 volts there.
I UNDERSTAND THAT. ***WHAT I DO NOT UNDERSTAND FROM WHAT IS GOING ON WITH MY SYSTEM, AND WHAT I THINK YOU'RE MISSING OUT ON IN THAT POINT, IS THAT I MEASURED DC VOLTAGE BETWEEN BATTERY (+) AND ALTERNATOR (BATT.) TERMINAL WITH + & - LEADS, AND I GOT VOLTAGE READINGS AS IF I HAVE MEASURED AT THE BATTERY, CONVENTIONALLY-SPEAKING. THAT IS WHAT I FIND SO STRANGE. ARE YOU TRACKING NOW?



There are six diodes in the generator. Those are one-way valves for the output current. They let that current flow to the battery, but when it's not running, they block current flow from the battery.
I UNDERSTAND: ELECTRICAL 'CHECK VALVES'.



By reversing the jumper cables, those diodes were "forward biased", and only the minute resistance in the battery cables limited the current. There is a limit to how much current those diodes can handle and that limit would have been exceeded by many times. Most cars have a very large 80 - 120 amp fuse bolted into the under-hood fuse box which might save the diodes, but when two of them short and allow excessive current, they follow that by burning open so the short is gone. The generator is destroyed, but the short is no longer in the circuit, just as if that wire to the output terminal was unbolted.
THAT THERE MAKES A LOT OF SENSE. HOWEVER, IT DOES NOT EXPLAIN [IN MY LIMITED UNDERSTANDING] ***WHY THERE IS VOLTAGE BETWEEN BATT. TERM AT ALTERNATOR (MEASURED AS IF IT WERE THE GROUND) AND THE + TERMINAL OF BATTERY.

IS THE ANSWER TO THIS QUESTION CONTAINED IN ABOVE?



If you don't have a large fuse for the generator, there may be a fuse link wire going to it. That is a small section of wire spliced in that is smaller in diameter so it's the weak link in the chain. The insulation is designed to not burn, and it will be a different color than the rest of the wire.
I'VE SEARCHED FOR FUSIBLE LINKS. I FOUND NONE. DOESN'T MEAN THERE'S NOT ONE THERE THOUGH. UNDERSTOOD.



You test them by pulling on them. If they're good, they'll act like a wire. If they're open, they'll act like a rubber band.
UNDERSTOOD.



Somewhere between the battery positive cable and the generator output terminal is a break in the circuit.
MAKES SENSE. (POSSIBLY LOCATED BETWEEN BACK OF ENGINE AND FIREWALL OF THIS SCION?)

BUT HOW DOES THAT EXPLAIN THE VOLTAGE I FOUND IN "***" ABOVE?



Many manufacturers use the generator's output terminal as a convenient tie point for the wires feeding other circuits. If yours does that, you might see more than one wire attached there. That would explain the dead starter relay.
ONLY ONE MAIN TERMINAL ON GENERATOR 'BATT' TERMINAL.



Also check the operation of the head lights or dome light. If those don't work either, check for voltage on any of the fuses. The smaller positive wire that is typically bolted to the fuse box may have burned open, or the smaller negative wire bolted to the body may have burned open.
GOOD INFO. THERE ARE OTHER ELECTRICAL ISSUES.



I APPRECIATE YOUR TIME, caradiodoc-FRIEND.

I think the confusion can be boiled down to one test. When you put one meter probe on the battery positive post and one on the generator's output post, you should get 0 volts difference but you're finding 12 volts. That's proof right there that something is open because those two points are in the same circuit so the difference should be 0 volts. What's happening is something in the generator is passing enough current to act as a ground path for the meter probe. There could be circuitry in the internal voltage regulator or even just the normal reverse leakage of a diode. Since it appears you have a pretty good understanding of electronics, it will make sense that a voltmeter is a very high impedance device. Whatever is in the ground side for that probe can have real high resistance; it won't matter to the voltmeter. A very experienced former coworker got fooled by that in the positive side, and in fact, it involved a fuse link wire. It had burned open but left a carbon track behind inside the insulation. There was no way that circuit could run the radiator fan, but with it unplugged and open circuit, his digital voltmeter read 12 volts at the connector. All it took was a tiny taste of current to sneak through for the voltmeter to pick it up. That's what's happening in the ground side in your case.

Being the smart tv repairman I once was, (I mean smart tv repairman, not that I once was smart), I suggested he take the same measurement with a low impedance test light. You should try the same thing. In his case not enough current could get through that carbon track to turn on the light. In that case, the inexpensive test light is more accurate than the voltmeter.

To say it another way, forget about that test for voltage between the positive battery post and the generator's output terminal. It's just going to create confusion. Instead, keep the negative meter lead on ground and just take voltage readings at various places starting at the positive post. In fact, I recently got confused on my van when the ground wire rusted off the body. I won't go into the details that mislead me, but to be safe, start with your meter leads both right on the battery posts, see your 12 volts, move the negative probe to the body, see 12 volts, then move the positive post down the line until you lose the 12 volts. Even better yet, do that with a test light if you have one.

I hope this doesn't make it more confusing but think of the wiring as a compressed air system in the shop. I had good results with this story with my students. Automotive people typically have a very hard time understanding electronics because they can't see it or manipulate it in their hands, but they can understand compressed air, or water in a garden hose. Your voltmeter is like the pressure gauge on the air system. No air flows THROUGH the gauge so the hole in the pipe where the gauge is attached can be very small. A 1/64" diameter hole is plenty for the gauge to display the pressure. Voltage is electrical pressure. As long as there is any amount of resistance, (within reason), other than an open circuit, the meter will detect the voltage and display it. If you try to run an air tool with the air that can get through that tiny hole, it won't run. Not enough air flow even though it appeared there was enough pressure.

What you might try is running a temporary new wire between the battery positive post and the generator's output terminal. It would be smart to do a resistance check first from the output terminal to ground to be sure nothing is shorted that will burn up that wire. That will restore operation if all that is wrong is something open in that circuit. You still want to find the problem though. In this case we know what caused the open circuit, but when students were troubleshooting my prepared cars, they didn't know the "history". They understood the correct repair involved finding exactly where the wire was broken or grounded because an entire harness could be laying on hot exhaust parts or rubbing on a sharp edge of a metal bracket, and it would just be a matter of time before the next wire would do the same thing.

Car-a-Diagnostic-Doctor (my new 'handle' for you), I want you to know up front that I appreciate the time, thought & effort you put into these replies. I would imagine that you are a very good Instructor too. I feel very confident that you are in fact.

You see, I was a Drill Instructor at Fort Sill, Oklahoma not long ago. And I've seen them all, believe me. Very few really care enough to go the extra mile . . . with anything it seems. I served with some of them on the 'Gun Line' (outside of Temporary Duty Assignments, which is what Drill Sergeant Duty is) at various times in my Career. They were no different there.

I don't mean to appear as though I am speaking ill of my comrades though. In most cases they all performed to the expected standards, and I guess that is where I and a few I [personally] know run into conflict here and there. What I mean is: Some Folks Give A Little More Than Others!

I would imagine that had you pursued the Military Career Management Field that I chose you would have been a Fast-Tracker too (Not Tooting my own horn here, okay). (Don't leave home and join the Army or Marines either, okay?)


Illustration is always a very good teaching tool, and you made excellent use of one in bringing into sharper focus what is going on with my vehicle. I'll use that method tomorrow morning under this new knowledge that it would take more draw to actually light up the filament of the bulb as opposed to registering on a Digital Multi-Meter.

My neighbor-'buddy', the fellow who hooked the cables up (I wished the dummy hadn't been drinking, but he doesn't trust anyone with his tools . . . even the Jumper Cables) has a 10-28V Test Light and a 12V Snap-On Test Light that I am sure of. Too, I'm sure that after all the trouble and expense he [accidentally] caused my requisition will be of little consequence to him. In fact, I'll probably try to get him involved in the process.

Caradiodoc, I want to thank you very much for your time. I wished I was able to somehow compensate you, for I know that Jim complains about that sort of thing periodically. Considering the dynamics of what is NOT normally required to make a Good Instructor, but a Excellent one in fact, and the care you demonstrated, I would have to say that you are a True All-Around Professional!

Again, thank you very much!

Wow. Thanks for the kind words. Looks like I got another one fooled!

Thanks too for fighting for my freedom. I'm a rather hard right-winger and very sad to see our country being torn apart by the idiot-in-charge.

One of my best friends flew Chinook helicopters in five wars over 30 years. He retired once, was asked back, retired again a year later, but was offered the chance to be in command of 5,000 men in Kentucky, as I recall. He turned that down. After moving back to town here in Wisconsin, he flew for one of the local hospitals for a couple of years. Got them certified for night flying too, but he gave that up recently to spend more time at home. I think he worked hard enough.

Thanks for all you do for such little appreciation.

Kind words? Don't mention it. I meant it.

And you don't have anyone fooled my friend . . . irrespective of what others, be they student, co-worker, or superior might have to say on the matter. I know!

I'm also familiar with the profile of your student. So take my word for it: You are an Excellent Instructor. CLUE: You Took The Time!

I've had to crawl down in a Foxhole at the Rifle Ranges, trading sweat with a Trainee who was having Marksmanship problems, and hadn't showered since the night before . . . just to try and figure out what his problem was. Again, I know!

Politics? Though a Military Man I do not lean one way or the other when it comes to Politics. Reason: The most you can ever hope for things to be good in our country (Economically, the Job Market, etc.) is 8 years (2 Successive Presidential Terms).

Beyond that, you have no guarantees that some idiot or other is not going to come along and mess it all up. Seems that it comes and goes in cycles . . . like the Army! I can no longer can put my confidence or hopes in a System like ours which is rapidly and successfully Deteriorating.


(CH-47D Chinooks? My youngest brother is about to retire as a Chinook Crew Chief. He's stationed up in North Pole, Alaska [Ft. Wainwright I believe]). Fly-Boys have a Mentality that is all together different, in fact opposite, of that of the Field Artilleryman.


Hey, one other question: As it relates to the possibility that the Alternator and its' associated Hardware/Circuitry is the problem, doesn't that rule out the possibility that there is a Fusible Link that is shot?

Thanks for your time. You keep up the good work too. This System of ours is also a Team, though there have been many outsiders on the playing field trying earnestly to disrupt things!

From above: "Hey, one other question: As it relates to the possibility that the Alternator and its' associated Hardware/Circuitry is the problem, doesn't that rule out the possibility that there is a Fusible Link that is shot?"

In other words, I'm getting a Voltage Reading.

If you have 12 volts at the generator's output terminal, (negative meter probe on ground), that would indeed suggest the fuse link is okay, but here again, use a test light for better accuracy. My reason for thinking is was open was under # 4 in your original post you found no continuity between the battery and output post, and under # 2, there was no voltage to any terminal in the starter relay socket. I'm having trouble calling up a wiring diagram to check, so I was hoping they used the output terminal as a convenient tie point for other circuits such as the starter relay and ignition switch. Many manufacturers do that rather than run longer wires from the battery post or fuse box. An open fuse link to the generator would make all of those circuits dead.

I sent an e-mail late last night to Mitchell On-Demand to see if they can help me get into the system. Once that works and I can see a diagram, I'll be able to give you some better tests to do.