FW: [s-cars] Mysterious Elec Problem - Temperature Warning Light always on

[Mike Bishoff]

I just ran a couple of diagnostics and I'm still stumped. :-(  

On the voltage check, I was getting about 0.5 volts on one lead and nearly
zero on the other. When checking resistance, I was getting about 1600 ohms
on one and pretty much zero on the other.

The 0.5 volts seems mighty low, but I'm unsure what the car is actually
providing to this circuit. And the 1600 ohms doesn't seem high enough. I
would have though it would have been more light infinite, but again, I'm
unsure what to expect.

Does anyone have a '92 S4 they could run a quick check on the blue and
yellow wires to see what voltage and resistance values are?

I need the following:

*  With ignition on - voltage supplied to both yellow and blue leads leading
to antifreeze tank sensor

* With ignition off - what resistance values for the same yellow and blue
leads.

Any other thoughts appreciated.

Mike

>>-----Original Message-----
>>From: Paul Gailus [mailto:gailus at mindspring.com] 
>>Sent: Thursday, January 20, 2005 10:28 PM
>>To: Mike Bishoff
>>Subject: Re: [s-cars] Mysterious Elec Problem - Temperature Warning
>>Lightalways on

>>Mike,

>>You might want to remove both the connector to the level sensor
>>and also the one to the MFTS with the engine off, start up the
>>engine, and then wait a while to see if the warning light eventually
>>goes out. The following note at the SJM site mentions that there's
>>some delay in the autocheck system before it responds to changes:
>>http://www.sjmautotechnik.com/trouble_shooting/cooling.html#warn

>>If this doesn't turn the light off, then you might want to measure the
>>voltage relative to ground at the blue/yellow wire on either of the
>>two connectors that were disconnected , with the ignition turned on.
>>If the voltage is nearly zero then maybe you've got a short
>>to ground somewhere. You could then check the resistance to
>>ground with the ignition off to confirm if there is such a short.

>>  Paul

----- Original Message -----
From: Mike Bishoff <mdbishoff at comcast.net>
To: 'Kent McLean' <kentmclean at mindspring.com>; <s-car-list at audifans.com>
Sent: Thursday, January 20, 2005 9:56 PM
Subject: RE: [s-cars] Mysterious Elec Problem - Temperature Warning
Lightalways on


>
> >Mike Bishoff wrote:
> >> I checked the anti-freeze level and it's well within the
> >> acceptable range.
>
> >My '89 200 was real particular about the anti-freeze level.
> >Make sure it is full, and not just within range.  If the
> >light still comes on, then look at the sensor(s).
>
> --
> Kent McLean
> '94 100 S Avant
> '89 200 TQ, "Bad Puppy" is no more
>
> The anti-freeze level is pretty much up at the top of the reservoir with
> just enough gap for expansion. I haven't had any problems until recently
so
> I'm assuming the sensor circuit, and not the switch, is at fault.
>
> I would think that I could *fool* the sensor by short-circuiting it and
> closing the switch and that would make the warning light go off, but this
> did not work. I'm assuming of course that the switch is NC when the tank
is
> full. Even so, I removed the jumper I used to short the leads making the
> circuit open and the results were the same.
>
> Any other ideas?
>
> Mike
>
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