Subject: [200q20v] Speedo off

[C1J1Miller at aol.com]

Joseph Vanzeipel writes:
==============
My speedometer is off by 5mph at ~75mph.  My car says 80 when in reality
it is 75.  How can this be fixed?  I assume it is an electric speedo,
unlike my 85 5ks, which was cable driven.

Thanks in advance,
Joseph Vanzeipel

91 200q20v (102k)
====================
Joseph:  here's a saved post off my 200q20v specific web site that might help.
---(http://members.aol.com/c1j1miller/body.html#Fixing the electronic 
spedometer)
Spedometer/Odometer 

I've also heard that this ground connection problem (see above) can cause 
problems with your spedometer becoming intermittant. 
------- 
Date: Tue, 25 Nov 1997 10:57:20 GMT 
From: paul.heneghan-at-bbc.co.uk (Paul Heneghan) 
Subject: Re: Speedo error 
From: "Smeins, Larry" <lsmeins-at-ball.com> 
------ 
My 87 5kcst has had a very optimistic speedometer from day one.  The odometer 
seems to be right on.  I thought I had a mechanical speedo and didn't 
especially want to pull it and have
it rebuilt so I put up with the error.  Now I find I really have an 
electronic speedo and wheels are turning on recalibrating it myself.  Where 
is the electronics for the speedo located?  Is it
possible to get at the calibration components to change them?  Has anyone 
done it?  My speedo seems to have a 5 mph offset from about 35 to 75 mph and 
then shows an increasing
error as speed increases.  It makes my passengers think I really drive fast 
and they are impressed by the speed and quiet of my Audi. 
------- 

Hello Larry - I posted this back in Feb 97.  If you want more info, I have 
the PDF file and also I drew out a circuit diagram of the speedo using 
CorelDraw. 
Here is some info I discovered on aligning the speedometer and setting the 
odometer on a 1989 Audi 100.  It will probably be of no use to the vast 
majority of readers on this list, but it
took me a long time to find out, so here it is anyway. 
I was given a spare speedometer with 90k on the odometer when I bought my 
Avant - it had been replaced a couple of times a couple of years previously 
because it went intermittent
and the fault was eventually traced to the sensor.  It is an electric device 
which uses a moving coil meter movement for the speedometer and a stepper 
motor to drive the odometer. 
The replacement speedometer showed a very low mileage (4338) and the true 
mileage of the car was 115k, so I connected the spare speedometer up to a 12V 
PSU and an audio
oscillator set to +12dBm, 600ohms, 315Hz.  The dividing ratio of the 
speedometer is 6644 (printed on the bit of paper stuck to the back, so 315Hz 
corresponds to 170.68mph). 
147 hours later, the odometer reads 115,000miles.  Please note that altering 
the odometer reading on a vehicle in the USA is highly illegal; to install a 
replacement odometer, you must go
to your registry and file the current mileage and the replacement mileage 
with your title. 
I also noticed that the speedometer wasn't very accurate.  30, 60 and 90mph 
should correspond to 55.4, 110.7 and 166.1Hz.  My speedo was close at 30mph, 
about 5mph out at
60mph and more than 10mph out at 120mph (not that I plan on doing much of 
this speed). 
The chip that drives the speedometer and the odometer is an ITT UAF2115.  I 
couldn't find any reference to this chip anywhere, so I e-mailed ITT.  They 
sent me a PDF file with the
data sheet for a UAF1025 which apparently is identical.  This shows that 
there is a series resistor connected to the speedo which is used to adjust 
the speedo sensitivity.  The resistor on
the circuit board was 51ohms.  I found that 54ohms gave a much better 
response along with a realignment of the mechanical zero position.  The 
speedo is now within 1mph between 30
mph and 60 mph and within 2mph over the rest of the useful range. 
Of course, the speedo is only accurate when the tires have the correct 
diameter, but the anal retentive amongst us could use a variable resistor to 
compensate for tire wear (just kidding). 
Note: These adjustments have no effect on the odometer.  That just divides 
the sensor pulses to give 1mile for every 6644 pulses. 
Paul 
paul.heneghan-at-bbc.co.uk 
1984 Audi 80 quattro 
1989 Audi 100 Avant 
======================
hth, chris miller, windham nh, c1j1miller at aol.com
'91 200q20v ==> http://members.aol.com/c1j1miller/