Auto check battery symbol keeps coming on

[Zeus]

Hi,

The yellow battery symbol of my autocheck system keeps coming on a few seconds after the engine is running, it then stays on until you switch the engine of again...
I've got this problem for over a year now and its very annoying
The car runs fine, and the battery is good too, never had any starting problems or whatsoever...

I've already tried another voltage regulator, another battery, charging the battery, cleaning the connections on the alternator and battery,... but nothing seems to help...

When the car is at idle and i disconnect the battery, the regulator puts out a nice 13.99V, with the battery on it stays at about 13.8V.

Does anybody have a clue of what might be causing this warning light to come on???

I'm getting really desperate to find it since it's so annoying...

[S2central.net]

What year is your car - I can look thru schematics to see where Autocheck gets this signal from - suspect it just a bad connection on that pin... Shouldn't be anything worse than that - unless the Autocheck module itself has gone bad.

[Zeus]

It's a '91 3B S2 coupe, hope it's a bad connector then, i've been searching for ages to find the fix...

[S2central.net]

On the blue connector behind the cluster - check you have battery +ve at pin 15 (purple/black)
And also on pin 19 of the yellow connector

While there check you have good earth (0V) at pin 8 on yellow and pin 3 on the white connector

[Zeus]

hey,

I checked the connectors you told me to check behind the cluster:

Blue connector is not getting +ve (12V) at pin 15, pin 15 is 0V, tested it with just ignition on and with engine running...

the rest of the pins were like you said:
yellow connector: pin19: +ve (12V)
pin 8: 0V
white connector: pin 3: 0V

So now I know its not getting 12V at the purple black wire... but how do I solve it?

[Zeus]

I've just tested the car with another instrument cluster... and it didn't give the battery symbol fault, so it's a problem with the cluster its self...
It didn't have the MIL light installed, which i do have installed in the original cluster, but i don't think that could be causing the problem could it?

So what could be wrong with an instrument cluster to cause this symbol to appear?

[Error404]

I have had an Autocheck go bad before, gave me the oil warning for no reason and beep then the beep constantly.. like

"beeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee eeeeeeeeeeeeeeeeeeeeeeeeeeeeeep"

That was annoying for the journey home before I ripped it out


Might just be bad connection like paul said, or Autocheck has failed

[Zeus]

Battery waning only beeps once, so it's not "rip it out" annoying , just normal annoying

Does anyone have schematics of the autocheck system itsself? Would be a great help at trying to find the fault.

[Nuvo]

Autocheck doesn't have a particularly high component count, you should be able to debug it without schematics. These particular schematics won't be available publicly either I'm afraid.

However, the factory wiring schematics will be helpful in identifying the pin that is used for the battery warning signal. Once you have that you just trace it path to its final destination which is the 8-bit mcu.

You're only looking at a handful of passive components and 1 or 2 transistors as I recall.

[Zeus]

I've switched the two parts of the autocheck system several times, and the battery symbol is only displayed when the original board with the fault display is installed. When I install the same board from the other instrument cluster I have, the battery symbol isnt displayed anymore. So I think this board is probably faulty.

So now I want to fix it, but I don't have any schematics of the auto check itsself. And I don't know which pin is for the battery signal, so I can't go checking everything on that route...

Does anybody have the schematics for the board below, if someone knows which pin is responsible for the battery signal that would be appreciated

[Nuvo]

Clicky

Take a look at the little 8 pin device LP2951 this is a programmable voltage regulator for starters.
Download its datasheet for the pin outs. Pin 1 is the output I'm sure.

[S2central.net]

Those T5c and T6g denominations are large pins on the cluster where the module connects... Its easy to buzz out from the cluster connectors to find them - I have done this in the past but never actually drew up a schematic of the board - that link from Nuvo will help you get the answr though.

[Zeus]

I checked the voltage regulator and its OK, delivers 4.96V with 12V input. And no visible oscillations, consumption was about 15mA.

I'm guessing the T5c connector is the black connector next to the display then right? (because the other black one doesn't have anything at pin 1). In the schematic it says that the alternator is connected to T5c/1, so that should be the right signal for the battery symbol right? What should this signal be, i'm guessing this is the starting power cable for the alternator (to get the initial magnetic field)???

In case this is the right pin, it leads to two resistors, one of these (100K) leads to the D75106G chip (the big one in the middle), and the other one (1K) leads to a lot of resistors, and is filtered with 2.2 uF to ground.

So i'm guessing the problem is the chip right????

[Nuvo]

Have you checked the wiring between the alternator and T26/21?
Forget that, I missed the detail above that you tried another board to isolate the fault.

The blue wire is the output from voltage regulator mounted on the alternator.

If you're not seeing +12V at T26a/15 then 15A fuse S12 is most likelyto have blown.
I would have thought you would have no power to the cluster if this is the case.
However that is at odds with the fact that it is working with the other board AND you have power.
Are you sure you're not getting +12V here?

What about T5c/2? This is the output of the voltage stabiliser J6.

[Zeus]

If you're not seeing +12V at T26a/15 then 15A fuse S12 is most likelyto have blown.
I would have thought you would have no power to the cluster if this is the case.
However that is at odds with the fact that it is working with the other board AND you have power.
Are you sure you're not getting +12V here?

Yes I'm sure, but i'll check later to be completely sure , and from what I can tell from the schematics, I shouldn't be getting +12V there... T26a/15 crosses the line with fuse S12, it's not connected to it, as far as I can tell, it's just connected to the fuel gauge sender G, which connects to mass, on the other side it is connected to a voltage regulator through the fuel gauge. So I cant get any power there with the cluster disconnected while measuring. But my fuel gauge is working fine so I guess the voltage regulator is OK too.

What about T5c/2? This is the output of the voltage stabiliser J6.

I'll try and measure this (T26a/16 to which T5c/2 is connected) in a moment, but T5c/2 isn't an output from what I can tell on the schematic, its just +12V feed for the autocheck I think??

thanks for the help btw