Here we’ll show you how to emulate the data that your instrument cluster works with. Why? So you can test it on a bench, change the operation of your gauges or lights, diagnose faults and failures, restore it to O.E.M. operation, or for any other reason.
Instrument Cluster Basics
There are two main types of instrument panels, one made by VDO, and one made by Motometer. They are mostly interchangeable (between manufacturers!), and function conceptually the same. It seems that the VDO ones have been designed for the Metric-based markets, and the gear drivetrain internal to the speedometer uses ratios that ultimately run the odometer in kilometers. The Motometer units feature a different drivetrain, intended for American or British markets, indicating distance driven on the odometer in miles.
The entire assembly is interchangeable subject to engine / speedometer / fuel gauge compatibility. As mentioned above, different markets had different speedometers equipped. Different engines likewise used different tachometer assemblies, and in fact, lower-equipped E30’s altogether removed the tachometer, instead replacing it with an analog clock. All tachometers and speedometers use a common connection method and run voltage, so, incompatible but semi-working instrument clusters can be robbed of parts that are in-and-of themselves compatible. The tachometer and speedometer are not soldered to the instrument cluster board, instead clipping in to a header pinout, likely because the clusters were assembled specifically for the vehicle.
Two types of fuel gauges were equipped in the E30- one for the split tank design, using two physical level senders in series, with one resistance of fuel gauge. This is the pre-facelift kind. The post-facelift kind uses a common level sender, and a simpler circuit, with a different resistance. The fuel level gauges are not interchangeable between configurations, and are soldered onto the circuit board. So, the fuel gauges (and thus clusters) may be separated into pre and post facelift variety. If you’re willing to solder, the fuel level gauges are modularly replaceable between boards, making this part irrelevant.
It’s also worth noting that there’s an engine-code plug (used for injector cycle rectification – 4 or 6 cylinders, keep reading for more information, in order to accurately run the tachometer and fuel mileage gauge). This coding plug will need to be swapped or accommodated if you’re swapping the engine. It appears this plug has been removed from newer clusters, so it may be blanked, and thus irrelevant for you.
The main instrument panel connectors are C1, the blue connector, C2, the white connector, and C3, the yellow connector. The blue and white connectors (C1 & C2) are for engine, chassis, and diagnostic signaling, whereas the yellow connector, C3, is for OBC data I/O. There’s also optional cruise control, connected to the instrument cluster through a green plug. We won’t cover the green plug here.
The instrument cluster was one of the primary “computer” modules equipped in the E30, other “computer” modules included the active check control (if equipped), the MoTronic ECU (if equipped), the cruise control computer (if equipped), and the anti-lock braking computer (if equipped). As you can see, it was one of the few common “computers” to all E30-models, despite engine configuration, and other features. Thus, it was responsible for the majority of the (admittedly few) calculations / electronic systems required to run the car. In turn, it does the majority of the processing required to run the on-board computer (OBC) if equipped.
Inspection System & Service Interval / SI Batteries
The Inspection Light system is a number of bulbs in the centre of your dash to remind you about servicing your car. The system is made of two parts; the “Inspection” light with its little clock symbol, and the LED bar of green, amber and red lights. These two systems are independent of each other.
The Inspection Light itself is a twelve-month clock which shows you how soon you’ll be needing a proper BMW Service; either Inspection 1 or Inspection 2, depending on what you have stamped in your service book. The system runs from a built-in timer powered by the SI (Service Interval) batteries; there are no sensors in your car which can actually tell whether a service has been done or not.
The LED light bar is your Oil change indicator, and is made up of five green, one yellow and one red. Up to five green LED’s will light when the ignition is turned on. However, the LED’s will extinguish once the engine is started, counting down to when your oil change is due. When the yellow light comes on, it’s time to change the oil. When the Red light comes on, this means that service is overdue by approximately 1000 miles. Once the service has been completed, the service lights should be reset. The system is partially intelligent; while based on a timer, it also checks engine temperature and distance travelled to calculate the condition of the oil. However, it has no knowledge about whether you’ve actually changed the oil or not.
If your Inspection lights constantly glow, even after being reset, this is usually a fault of the SI batteries:
To control a number of the instruments, batteries are fitted to the back of the circuit board. Many problems associated with the dash cluster are caused by failing or leaking batteries which need to be replaced. The SI batteries are powered by Fuse 27.
Two types of batteries were fitted during the production run; 1.2 volt NiCd batteries and 3.0V Lithium batteries. Most battery-related issues are caused by NiCd batteries. Placing batteries in a freezer for 15 minutes, then measuring their voltage, will determine whether they need replacing. If they measure low or zero volts, they can be replaced. NiCd and Lithium batteries are not interchangeable, but NiCd can be replaced with NiMh.
The batteries needed are CPC-Farnell, part # BT04235 at £1-79 each will do the job perfectly. These are tag ended AAA NiMH cells that are physically smaller than the originals (but with a higher capacity), which will allow you some extra room to fit them in. The tags aren’t the same as the originals, so note which end is +, and solder on some short lengths of wire to the tags to fit them in.
From: E30 Zone Wiki : Instruments
Internal & External Support Circuitry
The instrument cluster panel relies on a bit of external support circuitry in the vehicle, but the circuitry of the cluster is relatively straightforward. It’s covered in detail in the Electronic Troubleshooting Manuals.
The instrument cluster panel lights are the bigger removable light modules located on the back, as 90-degree rotation removable plugs. The panel lights are powered by the dash switch through pin C2-23 and dimmed through the dash switch dimmer through pin C2-24.
In order to do an LED conversion, this resistive dimming must be removed, or worked around. The resistive range covered by the dimmer is large enough to make this relatively complex to implement without an entire conversion or auxiliary circuit, as the LED’s will inevitably cut out at some minimum threshold of dimness.
For disassembly instructions, see our upcoming BMW E30 Instrument Cluster Disassembly Guide.
The OBC (On Board Computer) upgrade included a 6-button or 13-button digital control module with display, and an included ‘BC’ (Board Computer) control stalk on the steering wheel. The BC stalk was only included with the 13-button model. Both models provide time-keeping, temperature, and alarm functionality, as well as rudimentary driver alert signalling (sounding a chime / buzzer when the temperature drops, for example). The upgraded 13-button model also included a relay box to control a primitive immobilizer lockout system, operated through the ‘CODE’ button. For more information regarding the OBC operation, take a look at the E30 Zine Wiki.
The 13-button OBC additionally included speed limit alerting, fuel mileage tracking, digital average speed calculations, and a few other miscellaneous features. It relies on the instrument cluster to provide it with conditioned data via the yellow C3 connector, that is then processed by the electronics within the OBC. If your cluster is working, but your OBC isn’t, check the yellow C3 plug and ensure it’s snugly fitted, the manufacturing tolerance allows the connector to sit in a skewed position where it doesn’t completely make contact. If you’re OBC powers on, but your cluster is intermittent, you should be able to use the data provided by the OBC to isolate the issue to within the cluster, or the data it’s being sent. Most of the data is ‘bussed’ across, so if the data on both is wrong, it’s likely the data input. If the data does not match, it may be due to poor wiring connections (the logic signals must have clean SIGNAL and GROUND from the sensors to the computers), or a faulty component.
For more about the OBC, wait for our upcoming article about the BMW board computer.
Dash Light Indicators:
Most of the dash light indicators are centrally controlled through the common blue (C1) and white (C2) connectors, but lights that we’re related to equipment and systems that we’re only available in specific models were included as separate ‘plugs’ that stuck into the back of the cluster housing, illuminating a light channel just as the locking-plugs do. The difference is, they are powered by independent circuitry detailed in the models available with that specific equipment. For more information regarding the individually controlled lights, see the relevant Electronic Troubleshooting Manual. Lights controlled by their own subsystem include the glow plug light, check engine light, check transmission (gear) light, lower hazard light, and the anti-lock brake fault indicator light.
The rest of the dash indicator lights are controlled by either holding their circuit HIGH (+12V) or LOW (-12V) depending on their circuit implementation. We’ve provided a chart for quick-reference below:
DASH LIGHT INDICATOR PINS:
|INDICATOR||TRIGGER PIN||TRIGGER TYPE|
|BRAKE LINING||C1-22 / C2-26||OPEN|
Connector Pin Outs
C1 BLUE CONNECTOR:
- +12V START
- +12V CONSTANT
- CHECK INDICATOR (LOW)
- TACHOMETER INPUT
- FUEL RATE INPUT
- HIGH BEAM INDICATOR (HIGH)
- R/H TURN INDICATOR (HIGH)
- ALTERNATOR / BATT INDICATOR (LOW)
- BRAKE FLUID INDICATOR (LOW)
- OIL PRESSURE INDICATOR (LOW)
- BRAKE LINING INDICATOR LOOP 1
- SERVICE INTERVAL RESET (LOW)
- +12V RUN/START
- TEMPERATURE SENSOR INPUT
C2 WHITE CONNECTOR:
- PARKING BRAKE INDICATOR (LOW)
- FUEL GAUGE LEVEL SENDER
- FUEL GAUGE LOW INDICATOR (LOW)
- +12V START / RUN
- L/H TURN INDICATOR (HIGH)
- SPEEDOMETER SENDER GROUND
- SPEEDOMETER SENDER INPUT
- +12V ACC/RUN/START
- +12V RUN/START
- FOG LIGHT INDICATOR (HIGH)
- REAR FOG INDICATOR (HIGH)
- DASH LIGHTS POWER (HIGH)
- DASH LIGHTS DIM (LOW / DIMMED)
- BRAKE LINING INDICATOR LOOP 2
C3 YELLOW CONNECTOR:
- +12V RUN/START
- FUEL GAUGE LOW INDICATOR DETECT
- FUEL GAUGE LEVEL DETECT
- CODE/HORN RELAY POWER
- DASH LIGHTS DIM (LOW / DIMMED)
- +12V ACC/RUN/START
- OUTSIDE TEMP SENSOR SENDER
- DASH LIGHTS POWER (HIGH)
- +12V START
- +12V CONSTANT
- FUEL RATE OUTPUT/INPUT
- SPEED OUTPUT/INPUT
Testing The Cluster
You can test the primary function of the instrument cluster by supplying it with power in various states of ACCESSORY / RUN / START , by applying 12v + or – to the corresponding pins. The basic cluster itself and the indicators can be tested with basic tools or a small piece of wire, and a 12v – 14v DC source (battery, bench power supply, or other). In order to fully test the meters, you’ll either need a (ideally variable) resistor, and some sort of pulse width modulation function generator (see Function Generators or Portable Function Generator & Oscilloscope). Some multimeters or oscilloscopes will have a function generator built in, or you can buy a cheap & simple one online, or built a small circuit to generate the required frequency (and duty cycle). To connect to the individual pins, a breakout header jump lead is recommended. These can be purchased in kits online, and work best when the female-side shell is broken, and the socket slightly crushed prior to connection, for a secure fit.
Powering The Instrument Panel
To power on the instrument cluster panel, connect -12V (GROUND) to pins C1-20 , C2-15 , & C2-16. Then, connect +12V (POSITIVE) to C1-2, & C2-13. This will power the cluster on in accessory mode. To continue to run mode, connect +12V (POSITIVE) C1-23 & C2-14, and to emulate a start, momentarily connect +12V (POSITIVE) to C1-1.
Testing The Indicators
You can test the various dash indicators by supplying them with either a HIGH current (+12V POSITIVE) source or LOW current sink (-12V GROUND) source. The pins corresponding to the various indicators are listed below, and summarized at the top of this article. The fog lights, turn signals, and high beams will need to be supplied with +12V HIGH to run the indicator, whereas the others will need to be supplied with -12V LOW to run the indicator. The difference lies in how the indicator was integrated into the (entirely analog) support circuitry of the E30.
The brake lining indicator, if equipped, is noteworthy. This indicator works by relying on a high-resistance source through the brake pads to hold it low and prevent illumination. When the circuit is instead brought to open circuit (i.e. the wire breaks in the brake pad), the light cannot be held low, and illuminates. Thus, if you connect pins C1-21 & C2-26 , the brake lining indicator light will *turn off*. If the pins are not connected, the instrument cluster interprets this as a “worn through” brake pad, and the light illuminates.
Testing The Meters
- Fuel Level Meter: Use the center-leg of a 0-250ohm variable resistor to vary the level sender pin, -12V LOW will display “FULL” and +12V HIGH will display “empty”.
- Speedometer: The speedometer normally receives it’s input from a high-speed mechanical switch located in the differential, that as it switches between HIGH (+5-12V) and LOW (GROUND), effectively produces a pulse-width modulated signal, which is interpreted by solid state electronics within the cluster, and runs an electrical motor that positions the speedometer needle correctly. The electrical motor in turn runs a reducing gear train, in order to turn the odometer and trip meter. The elapsed distance interval (for service / inspection calculation) is integrated digitally, and stored on the SI (daughter) board. For the same frequency signal, the OBC will display a slightly lower digital speed than is displayed on the instrument cluster needle. This is apparently designed, and was common practice at the time. To run the speedometer, the instrument cluster will need to at least be in ‘RUN’ mode, and you’ll need to supply an appropriate frequency PWM signal at roughly 80% duty cycle. You’ll find a frequency-speed correlation table below, as well as a linear regression equation for converting a given run speed to a corresponding frequency.
- Tachometer: The tachometer receives it’s input either from an ignition coil parasitic circuit, a digital control signal from the MoTronic ECU, or from a hodge-podge of bussed interference in some other models. Regardless of the upstream signal source, the signals all arrive at the instrument cluster in the same way, as a pulsed signal where one pulse corresponds to one injector firing, or one full rotation of the engine. The MPG gauge receives it’s input in the same way, conditioned via the same source, usually. To run the tachometer, the instrument cluster will again need to be in at least ‘RUN’ mode, and you’ll need to supply an appropriate PWM frequency at roughly 60% duty cycle.
- Temperature Meter: Use the center-leg of a 0-250ohm variable resistor to vary the level sender pin, -12V LOW will display “FULL” and +12V HIGH will display “empty”.
The following tables can be used for determining the frequency at which to run the speedometer to produce a given speed, or alternatively, the frequency roughly produced by the diff speedo sender at a given speed. For the tachometer, they correspond to the frequency which indicates a given number of rotations per minute, and for the fuel mileage gauge, one pulse is sent for every complete injection cycle (1 per 6 injections OEM).
We’ve also included a simple linear equation for the graphs, for custom data processing applications.
SPEEDOMETER FREQUENCY CORRELATION: FREQUENCY=0.04818(SPEED) + 9.25184
|SPEED (km/H)||FREQ (Hz)|
TACHOMETER FREQUENCY CORRELATION: FREQUENCY=1.26356(RPM) + 5.63248
|TACH (rpm)||FREQ (Hz)|
We hope with the information provided you’ll be able to troubleshoot, repair, and restore your E30 Instrument Cluster. Stay tuned for more.
Credit to Jean @ The R3VLimited Forums for his post on the subject, which was the starting point for our testing and this writeup. Note: The post has the white/blue connectors reversed. C1 is the blue connector, C2 is the white connector, and C3 is the yellow connector. See The Post Here
Credit to guapoman2000 @ BimmerForums See The Post Here
See The E30 Zone Wiki for some other information about the Instruments