BRZ won't start. Cranks once.

[WNDSRFR]

Why is everyone here talking about voltage? The problem is current. A car battery can have 13 volts but hardly any current. That's why batteries are load tested not voltage tested. In a firehose analogy voltage is the water pressure. Current is the water volume.
The engine takes a lot of volume to turn over where lights take very little.
Ohm's law: E=I x R. Voltage is E, Cuurent is I and Resistance is R.

[Grady]

Originally Posted by WNDSRFR

Why is everyone here talking about voltage? The problem is current. A car battery can have 13 volts but hardly any current. That's why batteries are load tested not voltage tested. In a firehose analogy voltage is the water pressure. Current is the water volume.
The engine takes a lot of volume to turn over where lights take very little.
Ohm's law: E=I x R. Voltage is E, Cuurent is I and Resistance is R.

Yes current is a great check but current will be the same throughout the entire circuit. Voltage is what will vary depended on where your issue is. If you battery is bad with high internal resistance when you put a load on the system the battery voltage will drop. If your relay, fuse or wire is bad the voltage will drop after the issue not at the battery.

[NoHaveMSG]

Originally Posted by FR-S2GT86

The issue is that the '72 doesn't have sub-5 volt circuits in it that could easily be damaged by connecting a 12-volt incandescent bulb in series with them. Modern cars do, and the possibility exists that when you are probing for the suspected correct circuit, you might accidentally probe one of those low voltage circuits. Then you'll have to explain to your customer why they need a new ECU when all they originally dropped their car off was for a non-start situation....and you'll still have troubleshoot and fix the original issue once the ECU has been replaced and reprogrammed, etc. And you may have introduced even more issues to some of the low voltage circuits that the ECU is monitoring even after all of that. That is a risk that I would not take as a technician with many years of experience diagnosing vehicle electrical issues, and just about any other kind of electrical issue that you can think of.

For all of the old-school guys that still insist on using a "test light" to troubleshoot with, I would recommend a digital version of it such as this one here,


which as you can see has sequencial LEDs to show the level of voltage in the circuit you are testing, and can conveniently allow you to have one hand free if you attach an alligator-type clamp adapter to the end of the wired probe. The low voltage electronics in the digital "test light" pose no threat to modern electronics. Using a tool like this would be insurance taken to prevent a huge headache down the road.

Old school doesn't mean not effective, and most test lights I have seen recently are LED and have no effect on 5vdc circuits. Not to mention I hope you know what you are probing before hand, meter or test light. The most common control board we use here at work is 20 years old and is AC input, 5vdc for switching and controls. It is so sensitive if an AC unit or an air compressor is on the same breaker and kicks on, it would trigger some of the DC side signals. We now run filters on the DC side to prevent this, but a test light has never caused an issue with it. The control panel is always at least 60ft away so there is no way I am seeing that little test pen with different LED's for different voltages that far away, on top of the fact I am not looking to read voltage , I am just checking that it is switching. What Grady recommended would give me more information, but is not really necessary and for as often as I work on these, not cost effective. Now on to the OP's post.

Going back to the OP's first post, it doesn't sound like the battery to me. It sounds like something like a clutch switch as soundman98 said. Doesn't mean you shouldn't check the battery and if you are going to do that you should load test it which means the battery should be fully charged. So while you put a charger on the battery, that isn't going to stop you from checking other things, especially if the issue is indicating something else. By checking the starter terminal like RZNT4R said you are isolating where the issue is(which a test light is good for). Light comes on-weak battery, fuse, or bad starter/starter solenoid. No light- it's on the switching side. Clutch switch, starter relay.

[WNDSRFR]

Originally Posted by Kojiro

So I usually let my BRZ sit for awhile and I can normally jump start it.
Last time I tried to jump it, it wouldn't start.
Swapped in a good battery and it still had the same issue.
I installed a relatively new starter and left it alone for a few weeks and tried to jump it again today, but same issue.
What's strange is that it'll crank for maybe half a second and gives up. It is a push to start.
I checked some of the relays and they look fine.
I'll be getting a fresh battery tomorrow just in case, but has anyone have experienced the same thing?

I got a feeling it has something to do with the push to start thing.
Have no idea how that works. All my cars have had a manual start feature. (Turn the key untill it starts.)

[WNDSRFR]

Originally Posted by Grady

Yes current is a great check but current will be the same throughout the entire circuit. Voltage is what will vary depended on where your issue is. If you battery is bad with high internal resistance when you put a load on the system the battery voltage will drop. If your relay, fuse or wire is bad the voltage will drop after the issue not at the battery.

No voltage will be the same throughout the circuit. The current will vary with load.

[Tcoat]

Originally Posted by WNDSRFR

I got a feeling it has something to do with the push to start thing.
Have no idea how that works. All my cars have had a manual start feature. (Turn the key untill it starts.)

Even the keyed Twins are operating the same as the button ones. It just feels old school to put a key in a slot. Both are actually just a control that sends a signal to the modules that electronically unlock the steering and tell the starter to spin. The key is not working like switch and directly sending power to the starter.

[Grady]

Originally Posted by WNDSRFR

No voltage will be the same throughout the circuit. The current will vary with load.

Oh boy, even an a perfect circuit you will have a voltage drop across the conductor. In a defective circuit you will have a voltage drop across the defective component(wire, relay, fuse, ect) due to its resistance. This will lower the voltage to the end component (load). Yes the current will vary with load however the current will be the same throughout the entire circuit. Now the voltage will be divided up across all components in the system. If you have 12v at the battery and the relay has high resistance and has a 4v drop across, plus in a high current situation you have a 1v drop across the wire that means only 7v is getting to the starter motor.

[FR-S2GT86]

Originally Posted by Tcoat

Even the keyed Twins are operating the same as the button ones. It just feels old school to put a key in a slot. Both are actually just a control that sends a signal to the modules that electronically unlock the steering and tell the starter to spin. The key is not working like switch and directly sending power to the starter.

Yes, and with these push-button start cars, the ECU actually sends the 12 volt signal to the starter solenoid circuit after all of the checks are made such as the clutch switch, the park position or neutral safety switch on an automatic transmission car, the passive auto immobilizer circuit, the minimum operating voltage check, etc. if and when those pass the self check, which happens in milliseconds, THEN the solenoid will finally get the 12 volt signal it needs to energized the contacts to the starter motor.

One key thing, the minimum operating voltage check is there to protect the ECU from an under-voltage condition. If the ECU doesn't detect the minimum voltage as it gets the signal from the push-button for a start cycle, in order to protect itself, it will not attempt to energized the starter solenoid circuitry. Very low voltage on modern vehicles is equally, if not, even worse than high voltage conditions.

This explains why I often see issues such as someone leaving their vehicle parked for weeks at a time with a failing battery and coming back to start it up to find a dead battery. After the battery has been recharged or replaced, they start having strange electrical issues. Low voltage conditions for extended periods is normally the cause of these strange issues.

[RZNT4R]

Originally Posted by FR-S2GT86

The issue is that the '72 doesn't have sub-5 volt circuits in it that could easily be damaged by connecting a 12-volt incandescent bulb in series with them. Modern cars do, and the possibility exists that when you are probing for the suspected correct circuit, you might accidentally probe one of those low voltage circuits..

Your whole theory seems to hinge on probing wires willy nilly like (holy shit don't do this) piercing the insulation to "probe" a circuit and Ooops! ripping through the harness. BTW, a 12v test light doesn't supply 12v into a circuit, conventionally (with the clamp on ground) it supplies no voltage at all and waits for voltage on the pointy end, if you're daring and have the clamp on positive and touch the supply side of an accessory, you'll be sending about 6v into it, because you know, "voltage drop". That was how mercedes made you check the low voltage glow plugs on some year sprinters.

An incandescent test light is still used in some manufacturer supplied troubleshooting workflows right up to now, chrysler uses it A LOT, and yes, even in engine performance DTCs on circuits going straight into the ECM.

[WNDSRFR]

Originally Posted by Tcoat

Even the keyed Twins are operating the same as the button ones. It just feels old school to put a key in a slot. Both are actually just a control that sends a signal to the modules that electronically unlock the steering and tell the starter to spin. The key is not working like switch and directly sending power to the starter.

So with the push to start, do you have to hold the button until the car starts or do you just press the button momentarily and it automatically starts?

And as far as voltage vs. current goes: Suppose I have 8 AAA cell batteries in series and connect them to the starter. What do you think is going to happen? You have 12 volts. Why won't the car start?

[Grady]

Originally Posted by WNDSRFR

And as far as voltage vs. current goes: Suppose I have 8 AAA cell batteries in series and connect them to the starter. What do you think is going to happen? You have 12 volts. Why won't the car start?

Because when you close that circuit you will not have 12V at the battery any more. Why because of battery internal resistance.

[WNDSRFR]

OK
Let's say we replace the car battery with 8 AAA batteries. Turn on the key and all the lights on the dash light up. Now turn the key to start the car. What happens? Nothing. The lights on the dash go out because the starter is drawing all the current from the batteries.
So let's try it with 16 AAA batteries in series (24 volts). Turn the key on and the lights on the dash don't light. Because you just blew them up with 24 volts. Now turn the starter. What happens? Nothing because you don't have nearly enough current to do squat.

Battery internal resistance? Let's try lithium batteries. They have almost no resistance which is why they like to burst into flames. The results will be the same because you don't have enough current.

[NoHaveMSG]

Originally Posted by WNDSRFR

OK
Let's say we replace the car battery with 8 AAA batteries. Turn on the key and all the lights on the dash light up. Now turn the key to start the car. What happens? Nothing. The lights on the dash go out because the starter is drawing all the current from the batteries.
So let's try it with 16 AAA batteries in series (24 volts). Turn the key on and the lights on the dash don't light. Because you just blew them up with 24 volts. Now turn the starter. What happens? Nothing because you don't have nearly enough current to do squat.

Battery internal resistance? Let's try lithium batteries. They have almost no resistance which is why they like to burst into flames. The results will be the same because you don't have enough current.

But if you series and parallel 200 AA's together you could

[Tcoat]

Originally Posted by WNDSRFR

So with the push to start, do you have to hold the button until the car starts or do you just press the button momentarily and it automatically starts?

And as far as voltage vs. current goes: Suppose I have 8 AAA cell batteries in series and connect them to the starter. What do you think is going to happen? You have 12 volts. Why won't the car start?

If it doesn’t start right off yes.
You don’t have to hold the key either. You can just turn it and let go and it will automatically start if thing are working right. The only difference between the two is how the switch is allowed to activate. The key uses tumblers and the button is a security signal. That is all.
Hell even a physical key without the chip won’t work.
These are not a 55 Buick where turning the key physically allows current to run through the switch to activate the solenoid. The ECU does all that. Either way you are just letting it know you are ready.