Date: Sat, 27 May 2017 14:45:30 -0400
Reply-To: George Gaudette <gcgaudette@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: George Gaudette <gcgaudette@GMAIL.COM>
Subject: Only 5V at Temp II sensor?
Content-Type: text/plain; charset="UTF-8"
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