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Annoying flashing temp warning light.

2K views 7 replies 5 participants last post by  fatmobile 
#1 · (Edited)
Hi guys,

Is anyone able to provide some insight as to why my car's temp gauge's red warning light started flickering permanently? The gauge still works and indicates temp correctly but the light now flashes permanently. In the past when you turned the key on the light flashed a few times and then stopped as part of the self test.

The car is a 96 model Citi Chico, and it did not come with a coolant level sensor so it definitely isn't that for those whose were thinking that. I should mention that i had the instrument cluster out before it started, to clean the dials and re-paint the needles. When I did this and took it apart a small piece of thin cardboard fell out from somewhere inside the cluster. It's about 2cms in length and about 1.5cms in height with a little slit cut into it. This was a "factory produced" piece of cardboard not something someone else stuck in there.

Whether or not it's a coincidence or not but the permanent flickering of the warning light started directly after that. I have since taken it apart a few times again to try and find where this piece of cardboard could have been "installed" but have not had any luck. Any chance that the factory put this in there to disable the coolant level warning feature since this model didn't come with the feature. If so does anyone know where exactly it need to go back into so the normal functioning can return?

I have searched high and low on the forums and cannot find anything related to this specifically, only posts regarding faulty temp sender units and crappy wiring which this problem has nothing to do with. I should mention that I am from South Africa and that the car was produced at our VW SA Uitenhage factory.

Thanks Guys, happy motoring. :driving:
 
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#2 ·
The gauge itself can get cold solder joints and needs to be cleaned and soldered internally, but if it didn't do this prior then you did it post fiddling.
I would Plump the connectors on it, then make sure that your nuts on the back of the gauge are clean and shiny and tighten a wee bit.
I would also add a new ground from the Brown pin wire side of the connector to the Frame behind the cluster.

I have a how to post on grounds of the cluster and repair of a flaky water gauge in the Cabriolet forum FAQ's page 3 post 75.
 
#3 ·
Is it flashing or flickering?

If it is lighting up for even durations then you might have a system from a mk2.

Do you have a diesel?

The diesel had the light you describe. The temperature worked as you describe and the light would come on when the temperature got too high but it also had another feature.

It would flash if the water separator (mounted on/near the rear axle) got full of water. It was also notorious for failure as you describe.

That said, if you have a water separator you can drain the water out though the fitting on the bottom and the light should go out. If you do that, be VERY careful with the fitting. It is plastic and over 30 years old.

If you don't have a diesel and/or don't have a water separator then I have no clue. Sorry.
 
#4 ·
I also have an annoying flashing temp light

My temp light flashes after startup typically for +/-10 seconds until the battery voltage gets back to normal. If the battery is just a little drained it takes longer. If I turn on any lights BEFORE that flashing red light goes out, it keeps flashing almost indefinitely. I wait until the light goes out before adding any electrical loads.

I'm sure it's some kind of bad contact, but I haven't wanted to pull the cluster. The film-trace wiring that connects to it is, fragile.

It also could be that main wire from the alternator to the battery. Charging voltage seems good, but that wire is super old and the stock (weak design) Mk1 alternator connector probably needs replacing -nobody sells those, of course.
 
#5 ·
My temp light flashes after startup typically for +/-10 seconds until the battery voltage gets back to normal. If the battery is just a little drained it takes longer. If I turn on any lights BEFORE that flashing red light goes out, it keeps flashing almost indefinitely. I wait until the light goes out before adding any electrical loads.

I'm sure it's some kind of bad contact, but I haven't wanted to pull the cluster. The film-trace wiring that connects to it is, fragile.

It also could be that main wire from the alternator to the battery. Charging voltage seems good, but that wire is super old and the stock (weak design) Mk1 alternator connector probably needs replacing -nobody sells those, of course.
You could take it to a Automotive Electrical shop and they could rebuild it for you, or, you can convert it over to the Post type that the Cabriolet uses, which you can still get, and then you have one large lug to the battery and the itty-bitty one for the blue exciter, instead of the plug and pray one that was in the early westy years.
 
#6 ·
Mystery solved but no luck with flashing temp gauge.

Sooooooo,

I kinda feel somewhat silly now, but hey, it made sense to me the first time I thought of my previously mentioned suspicion. :) I finally found where the piece of "factory produced' cardboard needed to go. It's home was next to the clock and it's purpose was simply to prevent light from bleeding through to the other dials. So much for my theory. I found this out by stripping a friends cluster to see where it was. At the same time added his temp gauge to my cluster and it did the complete opposite of what I am experiencing. The light doesn't flash at all. No test sequence, nothing. Think it was disabled on his gauge or his gauge was broken worse than mine. Put back my temp gauge and back was the constant flashing.

It's still driving me insane but honestly I don't know what else to try anymore. Plumped up the connections, added better grounds, made sure all the terminals was clean and the nut tight. No luck, the problem has to be internal to the gauge.

Think it might have something to do with the little 8 Pin IC inside the temp gauge but don't have the knowledge to fix it if that is the issue. I just wish I understood how the circuit worked and what triggered the over temp flashing of the red LED. I mean the gauge is a toaster for pete's sake, how does the LED know "oh the car is too hot, I have to start annoying the owner by flashing".

If anyone knows the details of how this works please let me know. From my wiring diagram in my workshop manual it says the light is triggered by (ECU) not referring to Engine control unit, but referring to a "chip" (IC) inside the temp gauge or behind the speedo dial. Still makes no sense how the IC (ECU) knows the car is too hot and then starts flashing the LED.

Anyway, enough frustration for one day.

Cheers.
 
#7 ·
Placing the year of your mk1 would assist me in assisting you further as there are subtle differences in the gauges over the years.
Replacing the Gauge with out removing the faceplate to repair cold solder joints was a no-no. It thinks the Gauge is running overtly hot which is why it is flashing.

Here is the circuit out of my 90Cabriolet.


If you notice the IC denotion shows a Direct connection to pin2 ground, then there are 2 separate connections on the Gauge one from the input of the sensor, and the other from your 10V stabilizer. If the Ground point is cold soldered then you may be experiencing a FLOATed signal at ground to the IC This can cause all sorts of things to happen.

Guts of it with 2 cold solder joints, one being the ground and the other the Power.


Now also on my 90 I have a low coolant warning...and a relay type of controller prior.

but from the Haynes I have for a 81 shows the bulb is on a separate sender than the temp gauge and the light resides in the Cluster separate from the gauge.
My Bentley only goes up to 79....
 
#8 · (Edited)
On the one I worked on;
the circuit is an op amp.
A comparator.

Two inputs and it compares one to the other.

The temp sensor on one leg has a variable input
I think the coolant level sensor has and RC circuit.
The stable resistance in the coolant level sender gives a set voltage point
for the coolant temp gauge to compare itself to.

I can't remember if the voltage goes up as temps increase.

If the ground wire on the coolant level sender is not grounded
I believe the light will flash.

I had the coolant drain while driving and ruined an engine, got towed home.

So I took the jetta gauge apart and made my own board.
It bolts to the back of the gauge using the mounting bolts
that provide power and a connection to the temp sensor.
Level sender was piped in through the black/red wire.
I have a schematic around here somewhere but it's been awhile since I built this.

GTIdieselclusterrearview2 by vwfatmobile, on Flickr

The blue/white/black stuff is a true glow plug light only lights when they have power.
 
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