Date:         Sat, 27 May 2017 14:53:52 -0400
Reply-To:     George Gaudette <gcgaudette@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         George Gaudette <gcgaudette@GMAIL.COM>
Subject:      Re: Only 5V at Temp II sensor?
In-Reply-To:  <CAOXGjp=q16AqsHveD8tB5ePV+jr_yxh8Q5HnvqtqQxSc3w3Q+g@mail.gmail.com>
Content-Type: text/plain; charset="UTF-8"

CORRECTION -- I just looked at my dashboard and realize I was wrong to
refer to the "module behind the speedo".  I had to check, but the "always
on" brake light in the dash works normally (goes on and off when I work the
e-brake) when I disconnect the coolant temp / fuel level etc. cluster.  So
that's a heck of a lot more relevant to the temp-needle-not-moving issue, I
would think.  Not sure that it says anything about my 5V.

Fuel level gauge works normally.

-George



On Sat, May 27, 2017 at 2:45 PM, George Gaudette <gcgaudette@gmail.com>
wrote:

> Hi Volks,
>
> '90 water-cooled automatic camper here.
>
> My coolant temp needle stopped moving entirely some time ago.  The coolant
> blinky light works normally (blinks initially on startup then goes out, and
> has recently blinked for low coolant level).
>
> Today I obtained a bunch 100 Ohm resistors and fashioned them in various
> configurations to provide different levels of resistance when jumpering the
> wires that connect to my 2-wire Temp II coolant temp sensor/sender, as
> described here:
>
> https://www.thesamba.com/vw/forum/viewtopic.php?t=464113
>
> ...which is to say I hoped to validate that the temp gauge is in working
> order (including the wiring to it).
>
> The first thing to do was to check that there is 10V across those wires.
> Instead I found there was about 4.9V.  I tried with the negative lead
> touching a ground point instead of the brown wire, and got 5.3V.
>
> Using my various resistor combinations did not make the temp gauge needle
> move. I'm assuming those were moot tests because the low voltage prevents
> me from establishing working testing conditions. (Yes? No?)
>
> A second observation:  With the temp II disconnected and not jumpered, the
> idling motor revs to 1800 RPM.  When the wires are jumpered, RPMs drops to
> "normal" (which is to say on the border of stalling, with a little mild
> idle hunting).
>
> I assume I have to start testing the path that provides current to the
> positive wire.  I'm puzzling over the Bentley wiring diagrams as I am
> completely unknowledgeable and inexperienced mechanically -- I've always
> relied on a mechanic but am trying to build my skills and reduce expenses.
>
> Question 1: Has anybody seen low voltage at that location? Recall the
> cause?
>
> Question 2: What's up with that change in idling RPMs -- expected?
>
> Question 3 (Bonus question!):  Doesn't the ECU go into a "closed loop
> operation" when the coolant temp reaches about 100 degrees F?  And if so,
> would low voltage supplied to the temp II sensor cause the ECU to never
> switch to closed loop operation, causing poor performance? My van seems to
> run OK once warm, I'm just curious.
>
> FWIW / since some of you might recall: Yes, this is the same van with the
> short that causes the e-brake indicator light to remain on -- that is,
> engaging/disengaging the e-brake makes the brake warning light go on and
> off **if** I disconnect the module behind the speedo.  I have not resolved
> that issue.  I'm not implying that there's a connection between that
> symptom and my non-moving temp gauge needle; I'm too ignorant to know if
> that might be the case so I'm just throwing it out there to see what sticks.
>
> I would appreciate your thoughts on this if you have an idea.
>
> -George
> '90 Automatic Westfalia full camper
>
>
>
>
>
>
>