Instrument cluster swap

From E31Wiki
Jump to: navigation, search
Instrument clusters

All coding data for the body electronics module (EKM) and instrument cluster is stored in both units. This makes an instrument cluster swap a little more complex. When a new instrument cluster electronic backplane is bought from BMW it comes without coding data. Upon install it will automatically exchange coding data with the EKM when the ignition is turned on. This is, however, not the case with a used instrument cluster or instrument cluster electronic backplane which has coding data stored from another vehicle. The EKM detects the vehicle mismatch and refuses to exchange coding data. The gauges are inoperative and there is no odometer or trip meter reading. Instead the display reads EEEE to indicate a coding data mismatch. This forced BMW 8 Series owners with a broken instrument cluster to either buy an expensive new unit from BMW or to replace both instrument cluster and body electronics module with ones from a single junked vehicle. While the latter approach can be much cheaper than buying a new unit from BMW, the mileage reading and vehicle identification number (VIN) stored in these units obviously will be from the junked vehicle and no longer match the car they are now installed in. This article describes a method of installing a used cluster from a different vehicle without replacing the EKM or ending up with the dreaded EEEE, and with correct mileage reading – just as if it was a brand new unit.

Instrument cluster compatibility

Three different electronic backplanes were used for the E31 instrument cluster:

It is unclear what the exact differences are between these backplanes. The author successfully tested the instrument cluster from a UK May 1997 840Ci in a German July 1991 850i, but the electronic parts catalog (ETK) clearly states they are not exchangeable, so it's very well possible not all electronic backplanes work in all cars. When looking for a replacement instrument cluster it is recommended to respect the September 1990 and September 1991 part changes. That provides the best chances of getting an instrument cluster that will work. If getting a whole replacement instrument cluster (not just the electronic backplane), it may come from a different model in the 8 Series and even have different localization (for example 280 km/h versus 300 km/h speedometer or metric versus imperial). The front housing with the dials is independent from the electronic backplane and can be swapped between instrument clusters.


To remove the instrument cluster, the surrounding instrument cluster trim must be removed first. In some cases it is also necessary to remove the steering wheel, but normally there should be just enough clearance to take the instrument cluster out of the dashboard without removing the steering wheel.

Adjust the steering wheel to its lowest position and furthest towards the driver to gain more clearance to remove the instrument cluster trim. Locate and undo the two screws above the instrument cluster that secure the trim. Even after removing the screws the instrument cluster trim is still held in place by two hidden plastic retaining tabs – one on each side nearby the switches. Grab the trim on the top and pull as if trying to fold down. This should disengage the retaining tabs. Once the tabs are disengaged, the instrument cluster trim is loose. Pull the trim as far away as the wiring of the switches allows, then disconnect all switches. Note that all connectors have retaining tabs. The large connector on both light switches may be very tight. If necessary, use a large flat-bladed screwdriver to help dislodge these connectors. Once disconnected, the instrument cluster trim can be removed from the vehicle.

With the trim out of the way, locate the two screws on top of the instrument cluster that secure the unit to the dashboard. Undo the screws. Before proceeding, cover the steering column with a soft towel to prevent scratching the glass of the instrument cluster upon removal. Slightly lift the instrument cluster to release it from the two slots it sits in and pull towards the driver, then tilt to get access to the backside. Locate the connector on the backside, release its locking lever and unplug. Now pry out the instrument cluster from between the dashboard and steering wheel. If there is not enough clearance to remove the instrument cluster, it will be necessary to remove the steering wheel as well.


Instrument cluster front housing and electronic backplane

Unless a complete replacement instrument cluster was obtained with the same dial faces as the original instrument cluster and with the glass in equal or even better condition, the front housing with the dials from the original instrument cluster will be reused. Only the electronic backplane should be replaced. To remove the electronic backplane, tilt up the black plastic locking lever on top of the instrument cluster the full distance. This will partially open the instrument cluster. Pay attention for seals or stickers blocking the opening. Cut or remove them where necessary – it's not like there is any warranty left that can be voided by breaking the seals. When the locking lever cannot be moved any further, fold down the electronic backplane completely and pull out. Installation of the replacement electronic backplane is opposite of the removal.

It is recommended to test the instrument cluster before mounting and tidying up the dashboard – especially in the case of a used instrument cluster. Check the replacement instrument cluster has bulbs in all locations the original instrument cluster has ones. Then reconnect the plug to the instrument cluster and loosely insert the unit in the dashboard. Press and hold the trip meter reset button, then turn on the ignition and release the reset button. This will start the instrument cluster test where all gauges (should) move up and down from their resting position to maximum value. In some cases the tachometer moves up only to approximately 3000 rpm. Long as the movement is smooth, this is no cause for alarm. The odometer display shows revision and coding values and turns on all elements and pixels of the display. Note the program and gear indicator left from the odometer may seem to have missing pixels – this is normal. When ready, turn off the ignition to end the test.

Turn on the ignition again (this time without holding the trip meter reset button) and check the warning lights for broken bulbs. Finally turn on the headlights to check the instrument cluster illumination for broken bulbs.

If the replacement instrument cluster is new or a properly cleared used one, it will exchange data with the body electronics module for approximately ten seconds. During this period the odometer display is blank – so don't worry if it doesn't appear immediately. If nothing appears on the odometer at all after ten seconds but the rest of the instrument cluster appears to be working fine, check the two bulbs that illuminate the odometer display. If the odometer shows the car's mileage, the instrument cluster and body electronics module are properly synchronized. No further steps are necessary to enjoy your instrument cluster. If the trip meter reads EEEE, the replacement instrument cluster is used and still assigned to the vehicle it was previously installed into. Refer to the next chapter for instructions to recode the instrument cluster to the new vehicle.


Original instrument cluster in the 1991 850i with 240566 kilometers on the odometer
Used replacement instrument cluster from the 1997 840Ci reading EEEE due to coding data mismatch
Replacement instrument cluster properly recoded to the 1991 850i and showing the correct mileage

In the accompanying pictures the instrument cluster in a German 1991 850i with 240566 kilometers on the odometer is being replaced with the used instrument cluster from a UK 1997 840Ci.

People have gone to great lengths to get a used but cheap replacement cluster working in the BMW 8 Series – without much success though. Swapping or even recoding the 93C56 EEPROM on the printed circuit board doesn't work. The solution is in fact a lot simpler. Contrary to popular belief the used versus new state is not determined by the stored mileage or vehicle identification number. Brand new instrument cluster electronic backplanes do not come with a certain specific mileage or vehicle identification number preset which the EKM recognizes as being new. In fact the used state is simply determined by a flag in the coding memory and it can be toggled without soldering, although a computer with ToolSet 32 from the BMW Ediabas software suite is required along with a working interface to communicate with the vehicle.

With the replacement cluster installed in the vehicle, connect the computer with ToolSet 32 to the car's under hood diagnostic connector. Turn on the ignition. The trip meter will read EEEE indicating a coding data mismatch. Launch ToolSet 32 and select Load SGBD, Group file from the File menu. In the new Load SGBD, Group file dialog box, select control unit description (SGDB) file C_EKM.PRG and click Open. Several new windows open inside the ToolSet 32 window, including Select Job: C_EKM and Results. The Select Job window has a list of available jobs for the selected control unit and the Results window shows the output from the executed jobs. Select job c_kombi_gebrauchtbits_lesen near the end of the Jobs list. This job reads the instrument cluster used flag. Execute the job by selecting Start job once only from the Job menu or by pressing function key F5 on the keyboard. After a short moment the job output is printed in the Results window. Look for the used flag (GEBRAUCHT) in the output:


The used flag is set to 1 (true). This is what prevents the body electronics module and instrument cluster from exchanging coding data. Luckily ToolSet 32 offers a job that can clear the used flag: c_kombi_ungebraucht_setzen. Select this job in the list and execute it. After the job completed successfully and the used flag is cleared, the EKM considers the instrument cluster as brand new and starts the coding data exchange. This data exchange takes approximately ten seconds and during this time the odometer display is completely blank. Once the coding data is exchanged and both instrument cluster and EKM are synchronized, the mileage stored in the EKM is displayed. The old coding data, mileage and vehicle identification number from the car the instrument cluster was previously installed into, has now been overwritten with new data from the EKM. Execute job c_kombi_gebrauchtbits_lesen once more and look for the used flag in the output:


The used flag is now set to 0 (false or cleared). Despite just exchanging data with the EKM it still shows unused. In other words, the instrument cluster is not yet permanently assigned to the body electronics module. Immediately after data exchange a timer is activated which counts the operating hours with the ignition on. After eight hours of operation the used flag is toggled and the cluster is permanently assigned to the EKM. The timer is reset if the control unit is removed once again before eight hours of operation have elapsed. The instrument cluster can then once again be installed in another vehicle. As long as the instrument cluster is not operated for over eight hours in a single vehicle it can be exchanged between vehicles without clearing the used flag indefinitely. This is the so-called test phase. The test phase is not only handy for testing purposes but also interesting for BMW 8 Series owners looking for a replacement instrument cluster but without access to ToolSet 32: The clearing of the used flag does not have to be performed in the target car. It can be cleared in another car or even at a bench setup. A breaker, for example, could clear the used flag before shipping the instrument clusters to customers.

If preferred the used flag can be set with ToolSet 32 and job c_kombi_gebraucht_setzen but this is optional and absolutely not necessary since the flag will toggle itself after the instrument cluster is being used over eight hours in the vehicle.