B4 Passat TDI MFA Conversion
by Chris Bell|
It is possible to have an MFA trip computer in a North American B4 Passat TDI by installing an instrument
cluster from a Passat GLS (w/ optional MFA), GLX, or, for Canadian cars only, a Euro TDI. Unlike A4s, B4 instrument
cannot be reprogrammed for country codes. Because of this, U.S. B4s cannot use Euro or UK clusters; they must use U.S.-spec. clusters only. Canadian cars can
use either Canadian-spec. GLS (w/ MFA), GLX or European-spec. TDI MFA clusters. This article describes a
GLS or GLX cluster conversion only. Euro B4 TDI clusters are not covered, but they would make for a simpler conversion since these clusters would need no tach or MIL bulb modification.
MFA display functions include: Clock, Elapsed Time, Miles (km.) Driven,
Average MPG (l/100 km.), Average MPH (km./h.), Oil Temperature, and Outside Air Temperature. The MFA is switchable between
2 simultaneous trip modes. Trip 1 resets automatically after 2 hours of non-operation and can be
manually reset. Trip 2 can run continuously (during operation) for up to 10,000
miles/100 hours/264 gallons before it automatically resets and can be manually reset. This provides
very useful "trip-within-a-trip" capability.
It isn't quite plug-and-play, but the rewards are worth the effort.
The B4 TDI already has the ECM signals and most of the wiring in place to operate
Basically, you will be adding a used or rebuilt GLX or used GLS instrument cluster,
MFA controller/wiper switch, pulse frequency adaptor (required w/ GLX, optional w/ GLS clusters), 2 sensors, and assorted wiring and connectors. You
will remove your TDI instrument cluster, perform partial disassembly of
both clusters, interchange 2 parts
and add a new part. There is a small bit of PC board soldering required.
using a used cluster, you may want your odometer mileage reprogrammed by a specialty speedo shop to reflect your current
mileage (rebuilt GLX clusters from the dealer can be ordered with the car's current odometer reading).
You will then make 2 small wiring harnesses and install them along with
your new cluster, MFA controller, and 2 sensors.
- Tachometer (GLX & GLS) - When an unmodified GLX cluster is installed in
a TDI, the MFA works perfectly (after adding missing wiring, controller and sensors), but the tach
is no longer accurate. It reads 33% lower than it should in its new 4 cylinder environment. The tach calibration
cannot be reprogrammed, but the tach can be made to read correctly by inserting a pulse frequency adaptor inline with the
ECM's tach signal and installing the TDI cluster's tach face in the GLX cluster. GLS clusters can be installed in 2 ways:
a) Without the pulse frequency adaptor. The stock GLS tach face is utilized and a lower, TDI-appropriate redline is
graphically added to it.
b) With the pulse frequency adaptor. This approach is identical to the GLX option.
- MIL - The GLX/GLS cluster's MIL
LED bulb is the 3rd one in the right LED bank, which is the same location as the TDI cluster's glow plug
indicator LED. Furthermore, the GLX/GLS cluster has
no LED bulb
installed in the 5th (far right) position where the TDI's MIL is. So, if a GLX/GLS cluster were installed unmodified, the
GLX/GLS MIL would be fed by the TDI's glow plug indicator signal and there would be no MIL function for the
cluster at all. You must solder
in an additional LED bulb, 2 pull-up
resistors, and signal wire, and use the TDI's original black instrument surround (with proper identification of all
TDI warning lamps) to have MIL function with the GLX/GLS cluster.
- Odometer - Odometer display values are stored in the cluster's memory, not the
ECM's. When you change clusters, you change odometer values.
Used Cluster: You can have the GLX/GLS cluster's mileage value rolled forward or backward to match the car's current
value by a specialty speedo shop like Palo Alto Speedometer. Reprogramming
cannot be done by a VAG-COM or the dealer.
Rebuilt Cluster: If you go with a rebuilt cluster from the dealer,
the cluster can be ordered by the dealer with your current odometer value. Most dealers don't know that the mileage
can be ordered pre-programmed with these rebuilt
clusters (its done at the local VW parts warehouse or distribution center), so you may have to educate your dealer by having
the parts department manager call the warehouse/distribution center and verify that they can reprogram the rebuilt clusters
they have in stock. I have a good working relationship with my local parts department and was able to order the cluster
directly through them, without having to go through the service department, but you might not be so lucky. If you have to go
through the service department, they might not be willing to order and install an "incorrect" model cluster for your TDI.
So do try to order it directly through the parts department. If parts or service can't or won't order it with the correct
mileage (default mileage on rebuilt clusters is 0.0), you can always have it done by a specialty speedo shop. The upside
of going with a rebuilt cluster vs. used is that you avoid the possiblity of winding up with a cluster damaged by low voltage,
which is not uncommon for B4 clusters. The downside is cost. A sustantial core charge is required since you are not
exchanging "like-for-like" clusters, although this cost may be mitigated somewhat by not having to have the cluster
odometer mileage reprogrammed at significant cost (There is usually no extra charge for ordering a rebuilt cluster from the dealer
with reprogramed odometer mileage).
- Fuel Consumption Inaccuracy - When a GLX/GLS cluster is installed, the MFA MPG readings will probably be significantly optimistic,
depending on driving conditions and whether or not you have larger injectors, a chip and/or are using
The error can be reduced (to
about + or - 1.5% with stock chip & #2 Diesel) by adapting the fuel injection pump's Injection Quantity value with a VAG-COM. A physical IQ range adjustment may be required as well.
- B4 '95 GLS (w/ optional MFA) or '96-'97 GLX Instrument Cluster
Used - If you don't have a local source, try
Rebuilt from dealer - GLX P/N 3AO-919-930-FX. No longer available new. See "Tachometer issues", above.
Euro-spec TDI cluster (for Canadian cars only), see
this thread for a possible supplier.
Note: this is an A4 MFA thread.
GLS vs. GLX: A '95 GLS cluster w/ optional MFA is a good choice for this conversion if you want the lowest conversion cost and don't mind graphically altering the "too high" redline.
If you are going to use the pulse frequency adaptor, there is no adavantage in choosing the GLS cluster over the GLX. An MFA was an option in the '95 GLS, so, when
getting a used one from a wrecking yard, you should confirm that the cluster you choose has an MFA by measuring the size of the LCD
for the MFA/clock. It should be about 2"W X 7/8"H (vs. 1 1/4"W X 1/2"H for the non-MFA cluster). Used GLS clusters w/
optional MFAs will be
less plentiful than GLX clusters in the wrecking yards and may have limited availability rebuilt from the dealer.
GLX VR6 clusters, while more plentiful in wrecking yards and available rebuilt from the dealer (w/ your correct odometer
reading), require the installation of a pulse frequency adaptor, but they do not require any graphical modification of
the tach face.
- MFA Controller/Wiper Switch - Part #535-953-519-B-01C
- Oil Temperature sensor - Part #1HO-919-563
- Outside Air Temperature sensor - Part #357-919-379-A. This is optional. If you
want to save some labor time and don't care about having an outside air temp. display, the MFA
will work fine without it.
- Pulse fequency adaptor -
Dakota Digital SGI-8.
NOTE: A pulse frequency adaptor is not needed if you are using a '95 GLS cluster and will be graphically modifying the tach redline..
- 3 Multi-Pin Connectors and Wire - These are for fabricating the wiring harnesses for the MFA controller switch and
outside air temperature sensor. Part #s:
(1) 1HO-953-635 (MFA switch connector plug)
(1) 357-907-968 (MFA switch connector plug)
(1) 357-972-752 (Outside Air Temp sensor connector socket)
(6) 000-979-133 (connector wire w/terminals)
(2) 357-972-741 (wire seals for 357-972-752)
Bulk 18 gauge wire
- 1 yellow LED lamp & 2 resistors (820 ohm & 1.5K ohm, 1/4 or 1/2 watt). You can use a new bulb or
transfer the one from your original
I've tried to find a balance between not insulting anyone's
intelligence, and providing sufficient detail for a novice. As a result, you may have to refer to your
Bentley for some items, but I will bring up any points that Bentley leaves out.
A. Installing the MFA Controller/Wiper switch & harness
- Disconnect the battery
- Remove the driver's side under-dash panel and knee bar.
- Remove the 2-piece steering column shroud trim.
- Remove the air bag. After removal, make sure to set the unit down
with front side facing UP.
- Remove the steering wheel. Do not allow the clockspring to rotate.
- Disconnect/remove turn signal switch, then wiper switch. Slide the 3rd TS switch connector
off its locating groove under the steering column before removing switch.
- Fabricate a 4-wire harness (approximately 32" long) for the MFA controller/wiper switch. Use P/Ns 1HO-953-635,
357-907-968 and (4) 000-979-133 as the connector plugs and terminals/wire.
Unsnap, then unhook and rotate the fuse/relay panel down so that the backside is exposed. The panel should now be upside down,
oriented as shown in Figure 1.
The 357-907-968 connector plug has pin numbers stamped on it. The 1HO-953-635 connector plug does also, but the numbers
to read. Pin numbers for 1HO-953-635 are shown in Figure 2. View is of the wire end of the plug.
The relevant harness connections are as follows:
|MFA Controller/wiper switch
Pin wire color
|1HO-953-635 ("V" Plug)
- Install MFA controller/wiper and turn signal switches and new harness. The relay panel end of the
harness connects to the "V" socket in Figure 1. In the middle of the passenger's side end of the relay/fuse panel there
is a rectangular bar, flush with the panel side end (see Fig. 1). This bar extends throughout the width of the relay panel and locks
all of the connector plugs
to the panel at their inner ends. Before installing the "V" plug, pull this bar out (toward the passenger's side) to unlock
all connector plugs. Push it back in after installing the "V" plug. The MFA controller's
4-pin connector slides onto the 2 slots under the steering column right next to the turn signal switch
connector you slid off previously.
- (Optional) Replace shear bolt that clamps the ignition switch/steering column bearing housing to
the steering column tube. You will probably find that this shear bolt is loose, which causes excessive
movement of the steering
shaft and allows the steering wheel to be rocked up and down.
A shear bolt was apparently used as a theft deterrent, but you can replace it with a proper
socket head or hex head capscrew and install it with Locktite or
a lock washer. Remove the shear bolt by grinding or filing a slot in the "head" of the bolt and loosen it
with a screwdriver. It may already be loose enough to turn with your fingers.
B. Remove original instrument cluster
- Remove dash trim panel. Remove the 3 vent registers by grabbing the middle vane of
each register on one side with needle nose pliers. Pull straight out until that side releases. Then
repeat on the other side of each register. Remove the headlight switch panel by inserting a feeler
gauge (.025"-.030") into the gap between the upper edge of the switch panel and the trim panel above
it (just below the left hand vent register) at a point just to the left of the graphic symbol for the
instrument lights rheostat. After pushing feeler gauge in and to the right to release the panel
switch retaining pin, remove the switch panel. Remove 5 trim panel retaining screws and, then, the panel.
Slide diagnostic connector out the rear of the trim panel.
- Disconnect/remove the instrument cluster. Remove the retaining screw on each side of the cluster.
Pull the cluster straight out; it's 2 lower locating pins will release from the dash surround. Unplug the 2
connectors from the rear.
C. Partially disassemble TDI cluster.
- Remove cluster lens and black gauge surround trim panel.
- If using a
GLX cluster (or GLS cluster w/ pulse frequency adaptor), remove the tach needle and face plate. Use the procedure described in section D, below. This is not required if using a GLS cluster w/o pulse frequency adapator.
D. Partially disassemble GLS or GLX instrument cluster
- Remove clear lens and black instrument surround.
- Remove all gauge needles and face plates. First, rotate each of the speedo, temp., &
fuel gauge needles to their respective stops. While lightly holding each needle against its stop,
mark a pencil line on the face plate where the needle points when at its stop. Now try to remove the needles.
Using moderate torque, cautiously try to rotate them on their spindles when against their lower stops.
Be careful here; some needles may have
a very tight press fit and may snap off before they will turn, so use only moderate torque to try to
rotate them. If the needles won't break free and turn with moderate torque, STOP. If they do turn,
continue to turn while gentley pulling up and they will pop off. If they did
come off, skip to Step 3.
If the needles didn't come off, you now must remove them by pulling straight up without rotating. The first time you do this (you will
be doing it at
least twice) you may pull apart the 2-piece servo motor casings beneath the face plates rather
than pull the needles off their spindles. Don't worry, its not uncommon, but it will feel like
you have broken them. Usually the casings at first become only 1/2 separated and the spindle/needle
will be floating around at an angle. Just continue to pull straight up (not at the angles at which
they're leaning) until they feel like they are free (Note: the needles have probably still not
separated from their spindles...but the casing halves have separated). Since the face plate for the 2
gauges and speedo is one unit, you will have to finesse this a bit, trying to pull each of the 3
needles a like amount in stages. Once all casings are separated (or needles pulled from spindles...or
a combination of the two), remove the 2 face plates. Pull needles off of any spindles/casings that
came off as a unit with the face plates. Don't lose the rectangular spring washer installed between
the spindle and the upper casing half.
Reassemble any separated servo motor casings. Make sure that the dark grey plastic
reduction gear is installed on its shaft in the center of the lower servo motor casing. If not
installed, it got pulled off when the casings were separated. Find it and reinstall it, making sure
that the small pinion gear in the center faces up (the other side has a boss that is about the same
size as the pinion gear, so look carefully). Now install the spindle (with integral reduction gear)
into its bore. Rotate the spindle/gear so that the stop tab on the gear will fall into the free
rotation (1:00 to 11:00) section of the circumferential groove located in the underside of the
upper casing (rather than the 11:00 to 1:00 "stop" area) when the upper casing half is reinstalled (See Figure 4).
Now install the rectangular spring washer on the spindle/gear, convex side toward the gear, oriented
so that it will be located and kept from turning by the rectangular depression in the underside of
the upper casing half (See Figure 4). Now install the upper casing half carefully over the spindle to reintegrate
the servo motor casing.
- Remove the cluster PC board from its housing. Remove the 2 torx screws in the upper left corner of
the board. Locate the 6 board retaining tabs. See Figure 5.
From the front, release one tab at a time, lifting the board slightly to rest it atop that tab, and
continue around the periphery to the next tab, until all are tabs are free (the 6th tab in the
middle, accessible from the back of the housing, is probably not actually retaining the board, but
check to make sure). Remove the board.
E. Install yellow LED bulb, resistors and signal wire.
- Solder in yellow MIL LED bulb in the unused far right location. NOTE: If you don't have board
soldering experience or a 'solder sucker" device, I recommend farming this job out to an electronics technician.
If not using a new LED,
desolder/remove original TDI MIL LED bulb. Observe proper LED orientation as shown on the molded graphic
located between the 3rd & 4th LED on the right hand LED holder bank.
- Solder in the 2 resistors as shown in fig. 7. These enable the MIL LED.
- Solder in an MIL signal wire as shown in fig. 8. Install from the front side. Install
a male pull-apart connector on the other end. This will connect to what is now the only wire
on the second 28-pin connector on the cluster wiring harness.
F. Reassemble the GLS or GLX cluster.
- Reassemble in reverse order. Thread the MIL signal wire out the back of the housing.
The 2 Torx screws are tightened before installing the gauge faces. If using a GLX cluster or GLS cluster w/ pulse frequency adaptor,
install the tach face from your TDI cluster. GLS clusters not using a PFA, use the GLS tach face with graphic modification of
You may want to print out a small solid black rectangular graphic on a self adhesive mailing label that will
the "Unleaded Fuel Only" text on the fuel/temp gauge face.
When installing gauge needles, first turn the spindles to their respective lower stops, then JUST BARELY
PRESS THE NEEDLES ON. You will need to remove the needles again without pulling the servo casing
halves apart, so they should just be installed to a minimum depth that will allow them to rotate
on their spindles when at their lower stops. For now, set the needles at the index marks you made
(@ "0" for the tach needle),
but you will be reindexing them. Install the black instrument surround from your TDI cluster (with corrrect
warning light identification), but NOT the clear lens
at this point. Wire tie the MIL signal wire to the cluster housing.
G. Install pulse frequency adaptor
- Mount the Dakota Digital SGI-8. Wire-tie it to the HVAC duct below and to the right (passenger's side)
of the back of the light switch. There is a flat area of the duct facing forward.
- Wire the tach drive signal.
Locate the white tach signal wire. It runs from the #6 pin of the U1 harness connector
on the back of the fuse/relay panel (see Figure 1) to pin #10 of the instrument cluster harness connector.
Splice into this wire and run it to the
"Sig. In" terminal of the SGI-8 and return it to the splice via the "OUT1" terminal.
- Wire the Power and Ground. A convenient source for switched ignition voltage is the TV5 Terminal Wire
Connector. Its the only yellow 4-terminal Terminal Wire Connector stacked on top of the fuse/relay panel.
A convenient ground for
the "GND" terminal of the SGI-8 is the
round, brown multi-terminal ground point located above the driver's kick panel area near the fuse/relay panel.
- Set dip switches. Initial calibration ratios and dip switch setting are as follows:
GLX cluster - calibration ratio: 1.8824. Switch settings: 1-on, 2-on, 3-on, 4-on, 5-on, 6-on, 7-off, 8-on, 9-on, 10-on.
GLS cluster - calibration ratio: 1.2549. Switch settings: 1-on, 2-on, 3-on, 4-off, 5-on, 6-on, 7-off, 8-off, 9-on, 10-on.
- Test for low voltage signal dropout The SGI-8 is sensitive to voltage drop. You may find that the
tach reading will momentarily drop to zero when putting a large electrical load on the system.
With engine running, try simultaneously opening all 4 windows with headlights on and see if the tach needle
a split second. If so, and it bothers you, you can wire 12V+ to the SGI-8 directly from the battery via an
ignition-controlled relay, but this isn't necessary as the dropout doesn't hurt anything.
H. Installing Oil Temp. sensor
- Install in oil filter housing. Find the hex head plug to the left of the oil pressure
sending unit on top of the oil filter housing and remove the plug. Install the sensor, then locate and connect the female
spade terminal at the end of a solid black wire which should be floating somewhere above the filter adaptor.
I. Installing Outside Air Temp. sensor. (Optional - if not installing, skip to section I).
- Locate the sensor input wires. On the back of the fuse/relay panel,
locate the brown/white and white/red wires that originate from pins G1/2 and G2/2, respectively (see Figure 1). These wires will probably be taped together, bare-ended and unconnected at their other ends
- Make a harness. This is a long 2-wire that runs
all the way to the right lower corner of the front valance panel/spoiler.
Connect your harness to the 2 input wires and run it up to the upper part of the firewall, directly
behind the center of where the instrument cluster resides. Here you will conveniently find a rubber grommet
(where a speedometer cable once went on B3 models). Run your harness though the grommet, though the
cowl well and out through the second grommet in line with the first on the other side of the well.
From here thread it along the right side of the engine compartment and down the right front corner
to the 3/8" hole in the lower right corner of the valance panel/spoiler, where the sensor snaps in
from the back.
- Install and connect the sensor. Install the 357-972-752 connector socket (w/ 357-972-741 seals)
to the end of the harness and
connect the sensor. You also should wire tie the harness to the A/C
hose above the sensor location, since the sensor is not very securely located and may pop out of its
hole if you scrape the underside of the valance on something. This way it won't drag on the ground
if that happens.
J. Install Cluster
- Reassemble under dash items. Rehang fuse/relay panel. Reinstall knee bar and under dash
- Install cluster. Cut off the second 28-pin instrument cluster harness connector (the
one with only 1 wire) and install a female pull-apart connector on that wire. Connect/install the
cluster (be careful handling it, since the clear lens is off and you could damage the needles).
- Reinstall steering wheel, airbag and column shroud. Make sure yellow air bag lead
fits into slot in the column shroud. Turn ignition to "on" before reconnecting the battery.
- Check MFA and MIL function. Hopefully the odometer reading is what you expected. With
ignition on/engine off and MFA reset, the MFA should display 1:00 clock, 0 elapsed time, blank MPG,
blank MPH, 0 miles, blank oil temp. (if below 120 degrees) and ambient temp (unless you didn't install
the sensor, in which case, the display will be omitted entirely).
- Calibrate Tachometer. Hook up your VAG-COM and check RPM vs. tach readings @ 1,000/2,000/3,000/4000 RPM.
If the readings are off, make sure the tach needle is at "0" when rotated fully counterclockwise to its lower stop
and correct as
necessary. If its still off, refer to the SGI-8 calibration chart and choose one or more settings above or below
"cal ratio" 1.8824 for a GLX cluster, or 1.2549 for a GLS cluster, then
- Calibrate Odometer. Generally, if using stock OD tires, the odometer should be pretty accurate.
Test with a GPS, speedo dyno,
or mileage markers that are known to be accurate. If its significantly off, it can be corrected by installing a
Dakota Digital SGI-5 adaptor inline
with the VSS signal, but this would be an unusal condition with stock OD tires. An odometer correction
will require re-calibrating the speedo, so make sure you check the odometer before
- Calibrate Speedometer. Your speedo is most likely optimistic. The usual factory optimistic
speedometer reading is compounded by the fact that the GLX cluster is calibrated for a car with slightly different
tire size and gearing.
You can calibrate the speedo using a GPS, speedo dyno, or the MFA itself.
Correction involves re-indexing the needle below "0" when at rest. It looks a bit odd at rest, but once in motion, the speedo reads accurately.
Calibrating with the MFA: Unlike the speedo, the MFA displays average speed without built-in
optimism. So as long as the odometer proves to read accurately, so will the MFA average speed readings.
Re-indexing the needle will make a linear
change to the speedo (i.e., the differences in accuracy between high and low speeds will be identical
to what it was before re-indexing, but it will be more accurate at all speeds). So, choose a speed at
which you would like the speedo to be most accurate (I chose 65 MPH). Set your MFA to display avg.
MPH and, while maintaining that exact speed (according to your speedo), reset the MFA and maintain
the exact speed until the MFA displays a speed value. Stop and re-index the speedo needle on its spindle.
Recheck and repeat until its accurate. Also check at a different speed to make
sure there are no linearity problems.
- Calibrate fuel gauge (optional). This is really personal preference. I like the fuel
gauge to read just to the "full" line when the tank is full, and to the "0" white line as the car
sputters to a stop. Suit yourself.
- Calibrate MFA's MPG readings. MFA fuel consumption reading is calibrated by adapting fuel injection
pump Injection Quantity (IQ) by trial and error. The use of larger injectors, chips, biodiesel, or other engine modifications will affect MFA accuracy,
so before calibration, make as many of the changes you plan to make to engine and/or fuel as you can, or be prepared
to recalibrate with future changes. First, make sure that the odometer reads accurately so you don't compound fuel
measurement error with distance measurement error. Then, for the next several fillups, compare MFA average MPG readings
(in Trip 2, measured for the duration of each tank only) with accurate, consistent
station pump readings (i.e., at the same station, at the same dispensor w/ the same car orientation
and load, tank vented to the top). Then adjust pump IQ to correct after each fillup. If MFA readings are
numerically, than actual), increase pump IQ (numerically). Reduce IQ if readings are lower than actual. An initial
IQ setting of 3.8 mg/R is a good place to start before your first calibration fillup. Unfortunately, this can be
a lengthy process of trial and error. And remember, the MFA fuel consumption function is not intended to be a highly
its a rough interpretation of actual consumption and ranges above and below actual, depending on driving conditions. I've been
able to get accuracy down to + or - 1.5%. "Your mileage may vary".
L. Finishing up
- Finish cluster assembly. Make sure that, when finally pushing needles on more securely
after final calibration, you did not change the calibration! If not, then remove the cluster and re-
install the clear lens and reinstall the cluster. Disconnecting the cluster will erase all accumulated
values, of course.
- Reinstall instrument panel trim. And you're done! Enjoy your MFA!