Dead electrical system

2006 A1 LMTV has sat for a year and batteries have frozen so they will not even attempt to show a charge. If jumped with just 24 volts everything on truck is still dead. Yes both disconnect switches are on. Is this normal? Is 12 volts between batteries needed for something to enable?
Thanks, Tom

What does your meter read at the starter port? What does your meter read on the 12v side of the battery with the slave hooked up?

you are over thinking the question. assume 0 volts at the 12 v tap between the batteries. the batteries are just physically there but are way beyond ever having any volts. will the truck start?

You MUST have excitation voltage to the alternator before it will turn on. This only happens above a certain amount of oil pressure. Maybe you can excite the alternator with a seperate jump battery? Sorry do not know if it is 12v or 24v excitation. Think it is 12v.


Otherwise would think everything should still work if jumped "unless alternator is not perfect" in it's output; and nothing is perfect so if Alt. is just marginal then it may not produce enough "consistent power" to make all the computers happy thus things not operate. (and/or the polarity Box connections are an issue too). If alternator not doing well at all then I'd say not.

Test 12 and 24v output in the Power Distribution Panel when she is running to check if alternator is producing enough to run things?

buttt.... Tom your smarter than I on these things.. hopefully though gave you something of value mto ponder as you diagnose.

How can it run if everything is DEAD??

I have started A1 trucks that have been dead for years from GSA lots. Some run but the shift controller wont light up. Some do the disco on the dash.

No it wont start. It should spin but if there are no amps or volts on the 12v side nothing will power up

m-35tom said:

How can it run if everything is DEAD??

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Only enough alternator output to keep engine computer going but not enough for anything else? But then again that would not be "everything" though it may give that appearance?

BTW... can't tell from your post if your trying to figure out why it runs after a jump; but nothing else works.. .. or if you can't get engine to start much less anything else?

simp5782 said:

...No it wont start. It should spin but if there are no amps or volts on the 12v side nothing will power up

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is that cause you need 12v to excite the alternator once oil pressure is high enough?

Fuel solenoid requires energizing. On the A1s the transmission ecu does it all as it has no VIM

with 24 volt jump there is no starter no nothing. like I said and you don't seem to believe me, it is DEAD. NOTHING. Is this normal? there is NO 12 between the batts since they are very BAD. I just want to know if this is what would be expected on a 2006 A1 so I don't waste 3 days looking for a problem that may not be there.

m-35tom said:

with 24 volt jump there is no starter no nothing. like I said and you don't seem to believe me, it is DEAD. NOTHING. Is this normal? there is NO 12 between the batts since they are very BAD. I just want to know if this is what would be expected on a 2006 A1 so I don't waste 3 days looking for a problem that may not be there.

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In your opening post as written "dead nothing" and thread title is "Dead Electrical System" thus could easily be interpreted as "dead" is "specific to electrical system"; which is how it read at first to me and why questioned this later for clarity.

best of luck on her

Follow proper diagnostic procedures and you will have your answer. If the batteries are as dead as dead. Replace them since you are unsure. I have a good many A1 and P1 trucks with dead hawkers. They atleast have some type of dash power. If the batteries are reading 0 volts when you should have 12 start with the obvious before moving on.

Yeah I know all that, I just wanted to know if no 12v would keep EVERYTHING from showing anything. The first thing I will do is put 4 new batts in and see.

It should still have 24v to pin 52 and 53 at the p1 connector and 24v when cranking.

A1 trucks require 12 and 24 volts to start and operate. A lot of the relays operate on 12 volt. Slaving up 24 volts will not give you the 12 volts you need if your batteries are totally bad.

Suprman said:

A1 trucks require 12 and 24 volts to start and operate. A lot of the relays operate on 12 volt. Slaving up 24 volts will not give you the 12 volts you need if your batteries are totally bad.

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so the question is.. can one jump 12v in some place too to get her started.... assuming they have an alternator good enough to keep her running afterwords...... or will that not work on this more electronic-ized diesel??

What superman said. You must have 12V as all the starter control circuitry is 12V. A 24V jump is fine, but if the installed batts are so bad that they cannot complete a circuit to and float some current to the 12V in the middle of the bank, it wont work. The test for any basic no crank/start troubleshooting is to measure 12 and 24V AT the test points on the relay-breaker panel/PDP. Measure from each test point to the ground test point in the panel. No 12V and 24V, no workie...

How to get around this?
1. Remove the bad batts and install two good ones from whatever you are using to jump it.
2. Go buy two gr24 or larger batts and install them where an inner and outer battery used to reside.
3. Hook up your nato jump cable and add another jumper cable from the 12V point in the middle of your 24V jump source to the 12V point in the vehicle bank. Least desired! Since the alt is sensitive to what it sees as a load, with installed batts so far gone that they will not complete a circuit to 12V from a 24V jump, the alt may drop off-line as soon as you try and remove the jump source and the vehicle will die from lack of power... this could be hard on the ECU’s and alt/reg...

#2 would be my preferred. The truck should start and run fine with 2 batts, just cover the unused terminals so they don't short to anything...

And the A1 trucks are especially sensitive to low voltage. They don’t like it and won’t operate.

From the A1 schematics, 12v BATTERY voltage is required to provide 12v IGNITION (logic line) needed by several modules.

The 12v IGNITION logic line comes from K2 relay which has a 24v coil but its 30 and 87 contacts close the connection from 12v battery voltage to 12v ignition control line. If there is no 12v battery voltage (at X2 Junction Stud) then the 12v ignition logic line cannot be pulled up, then presumably “no start” in spite of the fact that the main start components are 24v.

If you are jumping 24v to the truck, the two batteries in the 12-24 position must be very high resistance and therefore don’t pull up the 12 volt point between the battery pairs. In other words, the voltage divider normally provided by the 0-12v pair of batteries and the 12-24 pair of batteries is biased way down toward ground, zero voltage.

Of course your initial question was if 12v is needed to do anything. Looks like the answer is YES.

Interesting and fun theoretical question Tom.

New to the group and first post. So I have the same issue with a truck I just bought. If I'm just going to put new batteries in it, does it use the same 6TL batteries that have been around a long time? I know there's four of them.