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The gauges |
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The gauges installed in Cabriolets allow for
easy monitoring of the engine's oil temperature, oil pressure, electrical
system, and coolant temperature. While these gauges are not 100%
accurate 100% of the time, they help keep the driver from being surprised by
a change in engine performance. The gauges show changes in engine
condition before the condition reaches a critical status. While
the gauges will alert you to changes in engine performance, they will do you
no good unless you understand what they are telling you. |
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Console
gauges & what their normal readings are |
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Volt |
Bar |
°Cels. |
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(displays condition of charging system)
Normal range is 13 to 14 volts with slight
dip to 12 when accessories are on/running and at start-up |
(displays oil pressure)
Minimum of 2 bar at 2000 rpm and engine oil
temperature at 80°C (2 bar = 29 psi) |
(displays oil temperature)
Normal operating temperature range is
between 100°C and 120°C (100°C = 212°F) |
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A voltage reading of
15.5+ means the alternator is overcharging the system. Causes:
faulty voltage regulator and/or weak battery.
A voltage reading of less
than 12 with all accessories running usually means that the alternator
is not charging. Causes: loose/slipped belt and/or faulty voltage
regulator. |
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At start-up,
the 
light is on; when revving the engine the light goes out |
| This is normal. Current
from the battery to the alternator is routed through the charging system
warning light in the instrument cluster via a blue exciter wire. Once
the alternator's output equals the battery's voltage, the warning light goes
out, indicating that the alternator is now charging the battery (volt
gauge jumps from 12 to 13-14). The point at which the light goes out
varies between cars, but it's generally between 1100 and 1600 RPM. |
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Normal water/coolant
temperature reading |
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The needle should be
around or on the light under normal operating conditions. In
stop-and-go traffic, drive-thru lanes, etc., needle may climb higher
(this is due to little air flow through the radiator).
If the light
begins to flash it is an indication that something may be wrong (low
coolant level, V-belt damage, cooling fan failure, coolant leak, etc.).
Usual operation: needle climbs to the right edge of the light, fan
turns on, needle drops to left edge of light, repeat. While
cruising, the needle generally stays over/on the light. |
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If the needle pegs to the right and the
light flashes at start-up and remains this way, test the coolant temperature gauge sender
as it may be faulty. If coolant gauge is reading low (needle
stays to the left of the light), it's indicating that the thermostat
is most likely faulty. |
 What temperature
corresponds to the needle reading? Very good question!
It all depends on what thermo switch is installed in your radiator.
The standard, OEM thermo switch is a 95-84° switch. This
means, for single- and two- speed fans, the radiator cooling fan
will turn on at 95°C (203°F) and run until the coolant temperature
in the radiator is down to 84°C (183°C). So, if you have the
standard thermo switch in the radiator, when the needle reaches its
highest point on the gauge and the fan turns on, the needle is
showing a coolant temperature of approximately 95°C (203°F); with
the needle directly over the light, the coolant temperature is
approximately 89°C (193°F) (I say "approximate" because, as stated
elsewhere, these gauges are not 100% accurate). |
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Warning
lights |
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The gauges are pre-indicators of possible
issues. Failure to heed the gauges' warning signs will result in
blinking warning lights, which could lead to costly engine repairs.
While the problem could very well be a faulty gauge sender, it's better
to rule out the simple things than to be stranded on a deserted highway
with, worst case scenario, a blown engine. The dash warning lights should all light at
start-up and go out within a few seconds; if any or all remain lit,
there's a problem (electrical and/or mechanical) that needs to be
addressed. |
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Turn indicator light =
flashing: turn
indicator is on; steady-on: fault in the indicator circuit |
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Alternator light =
indicates a problem with the charging system |
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Oxygen Sensor light =
indicates that it's time for an oxygen sensor replacement (every 30,000
miles); 1988+ Cabriolets do not have this warning light (sensor
replacement interval is 60,000 miles). 1980 Cabriolets have EGR
lights indicating it's time for an EGR valve replacement. |
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Oil pressure light =
indicates that engine oil pressure is too low & is usually accompanied
by a buzzer |
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High beam light = indicates
high beam lights are on |
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Up-shift indicator light
(manual transmission only, up to '87) = for best fuel economy, shift to
next higher gear when light comes on |
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Airbag warning lights =
indicates that the airbag system needs servicing (when the lights are
lit, airbag system is inoperable) |
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Check
engine light |
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The check engine light
usually means that there is a fault in the emissions system. Performing
an OBD I scan will a) tell you what the problem could be and b) clear
the code(s) and turn the light out. Only California Digifant I
Cabriolets have the check engine light. The OBD I scan tool port is
under the shift boot, towards the front (OBD II scan tools cannot be
used to read OBD I codes).
Click here for
a list of fault codes. |
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Oil
pressure light flashes at idle but not while driving & oil level is fine |
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More than likely, the problem lies with
incorrect oil weight, incorrect oil filter type, oil sending unit is faulty,
and/or oil sensor(s) is faulty.
Click here
for further information on the warning system and how to test it.
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Oil
pressure light flashes and/or the buzzer sounds at start-up, but oil
pressure is fine |
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More than likely, the problem lies with a
faulty oil pressure switch.
Test the high-pressure switch on the oil filter flange by raising the engine
rpm up to over 2000. Remove the blue-black wire from the switch and
connect it to ground. If the buzzer stops buzzing, the switch is
faulty and should be replaced. The 1.8 bar pressure switch is normally
open until proper oil pressure closes it, completing the path to ground.
Test the low-pressure switch on the cylinder head by removing the yellow
wire; if the warning light stops flashing, the switch is faulty and should
be replaced. The 0.3 bar switch is normally closed until it senses low
oil pressure, at which time the switch opens, breaking the path to ground.
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The OXS
(or EGR)
light is on |
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The table above explains why the light is on.
To turn the light off, carefully press the white (or red) button on the
counter box (black
box located behind the coolant reservoir and attached to the firewall)
all the way in using a pen or the eraser-end of a pencil.
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The air bag
lights are on |
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The lights are on because a) the pre-determined
service time has passed; b) there is a fault in the air bag system; c) work
was done to the electrical system without disabling the air bag system
first. When the air bag lights are illuminated, the air bag system is
"off"; i.e. the air bag will NOT deploy in an accident. If disconnecting
the battery for one hour does not reset the system thereby turning the
lights off, the car must be taken to your local VW dealer for servicing.
For more information about the airbag system, please see the
airbag system page.
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The turn
signal indicator light is dimly lit & gets brighter when activated, but
doesn't blink as it should. |
| First, check fuses #4 and #19
(1980-1982: #6 and #8). Usually, one or both fuses have blown.
If a fuse is blown, replace it. The indicators should now work; if
not, re-check the fuses. If the fuse has blown out again, there may be a
faulty ground somewhere in the turn signal circuit. If the fuses are
fine, check the hazard switch (turn signals are wired through the hazard
switch) and replace if necessary. If all of the above doesn't fix the
problem, check relay 12 (1980-1982: relay 9?) and replace if necessary. |
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Speedometer/odometer
issues |
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Speedometer works, but the odometer doesn't:
The odometer gears are broken
and/or out of alignment.
Click here for a repair how-to,
or click here to buy new
gears.
Speedometer doesn't work:
The
cable has most likely become detached from the instrument cluster. For
those cars with oxygen sensor counter boxes, the box and/or its attachment
points could be faulty. Another possibility is that the cable's drive
gear in the transmission has become faulty, or has gone missing.
The speedomoter bounces and/or squeaks:
It
may simply need lubricating: Detach the cable from the instrument
cluster and/or OXS counter box (attached to firewall, up to '87 models).
Spray Tri-Flow or like lubricant onto the cable shaft; hold the cable
upright for a minute and re-install (for 2-piece cables, lubricate both ends
that mount to the OXS counter box). If this does not solve the
problem, replacing the cable is most likely necessary.
The speedometer is reading a bit faster than your actual speed:
Replace the main ground cables and clean all other ground points. If
that does not help, remove the speedometer and make sure there is enough
spring tension on the needle. If the tension is lacking, carefully
remove the needle, wind the spring, and replace the needle.
The speedometer is reading much faster than your actual speed (ex. reads 60
when you're actually going 30):
The
speedometer is broken and must be replaced. NOTE: Be sure to replace
the battery ground cables first, making sure the contact points on
the body and transmission are clean (1990+: also make sure that the Digifant
ECU ground in the rain tray is clean and tight). If the car has poor
grounds the electric current will seek a less-resistive path, which
sometimes becomes the speedometer cable leading to the speedometer itself
being destroyed internally.
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Can I replace the 2-piece
speedometer cable with a one-piece? If so, what about
the black box? |
| Yes, the 2-piece cable can be
replaced with a one-piece cable. For the early Cabriolets, be sure to
double-check what type of connector your car has (clip-on or twist-on;
1980-1981 came with twist-on) before ordering a new cable. For the
clip-on types, simply buy a one-piece cable for a 1988-1993 Cabriolet (German
Auto Parts sells a direct replacement for manual transmission cars).
It should be noted that the upper cable is no longer available; if you're
needing to replace both cables, you will most likely need to convert to a
one-piece cable.
As for the OXS counter box: The box is nothing
more than a mileage counter. When replacing the 2-piece cable with a
one-piece, the counter box is no longer useable. Therefore, simply unplug
the box's electrical connector and toss the box into storage or a trash
bin, or sell it.
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Cable |
Location |
Transmission |
Cable Length |
Part Number |
| Lower cable |
trans to box |
manual |
|
171 957 809 B |
| Upper cable |
box to speedometer |
manual |
|
n/a |
| Lower cable |
trans to box |
automatic |
560mm |
171 957 805 B |
| Upper cable |
box to speedometer |
automatic |
|
n/a |
| One-piece cable |
trans to speedometer |
manual |
1100mm |
191 957 803 D |
| One-piece cable |
trans to speedometer |
automatic |
970mm |
171 957 803 F |
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What the speedometer
number
means. |
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The number below the
MPH or km/h on the speedometer side of the instrument cluster is the
calibration of the speedometer to its transmission gearing (or: the
number of revolutions required by the speedometer cable divided by
100 to travel a distance of 1/100th of a mile, which is 52 feet, 9.5
inches).
Cabriolets use 1540 speedometers, whether it's a VDO or Motometer
instrument cluster. USA speedometers are
calibrated for 1000 RPMs at 60 MPH, while European speedometers are
calibrated for 1000 RPMs at 100 km/h. Cabriolets (and their
Scirocco counterparts) use European-calibrated speedometers.
If your car has an instrument cluster from another model, simply
divide 1540 by the calibration number on your car's instrument
cluster to obtain the approximate speed difference percentage.
For example, if your car has a 1707 speedometer, the formula would
be: 1540 / 1707 = .90, which translates into your speedometer
reading 10% slower than what it should be. |
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