Instruments

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Contents

Dash Cluster

The E30 was fitted with a multi-instrument binacle featuring all the standard clocks and dials expected of a car. A Speedometer, fuel guage and coolant temperature gauge were standard across the range, while all M20 models received a Tachometer (rev counter) and econometer as standard.

Learn more about replacing your Dash Cluster. Learn more about Changing your dials.

Wiring

The dash cluster is a one-piece circuit board inside a plastic shell, mounted to the dashboard. It receives its information through two plugs (white and blue) connected to the rear of the circuit board. These plugs are fed information from the main loom through the C101 plug, which is attached to the bulkhead inside the engine bay. If you have changed your engine, especially for a non-E30 engine such as a M50, then rewiring the C101 plug is essential for making the dash cluster work properly.

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.

However, if the SI batteries have leaked, the entire circuit board will need to be replaced.

Learn more about replacing SI batteries.

Coding Plug

Inside each dash cluster is a coding plug, which is specific to each engine, be it a 4-cylinder or 6-cylinder unit. When replacing your dash cluster with that from a different model, it is an incorrect coding plug that causes instrument problems.

The coding plug can be accessed by removing the plastic trim around the instrument cluster; the cluster itself does not need to be removed.

Individual Gauges

Speedometer

The Speedometer tells you how fast your car is going. It takes this measurement from a sensor inside the differential, which means that the displayed speed is dependent on the size of wheel and tyre you are using.

E30 speedometers are calibrated to display a higher-than-actual speed, which was common among manufacturers at the time.

If your speedometer has stopped working, click here.

Cruise control systems require speed information to work properly. A green plug connects to the back of the dash cluster with provides additional pins to which the cruise control can be connected.

Odometer

The odometer, or mile counter, is a simple system of mechanised wheels and gears, powered by a small motor. Over time, the small plastic gears that drive the wheels become brittle and break, especially in hot-weather countries. Removal of the odometer is simple, but the only practical solution is to replace the entire dial.

Fuel Gauge

E30 Fuel gauges are a standard needle gauge, fitted with an orange warning lamp when the tank level reaches 8litres.

The E30 was fitted with two different fuel tanks, a 55 litre and 62 litre. Depending on which tank the car has, a specific fuel gauge is installed in the cluster, which are not interchangeable. A 62 litre gauge connected to a 55 litre tank will still read half when the tank is empty, while a 55 litre gauge connected to a 62 litre tank will read empty when the tank is still half full.

Fuel gauges can be identified by a label on the side of the gauge.

If your fuel gauge isn't working, click here.

Temp Gauge

The E30 temperature gauge is not linear - it's compressed at each end, with the whole centre section from just clear of the blue to just before the red, covering just a few degrees. The needle anywhere is this whole section is fine according to BMW. In practice, E30's have the needle just past the 1/4 mark, or almost exactly on the centre mark, depending on the thermostat fitted.

The temperature is taken from the engine using a simple heat-dependant resistor, known as the Brown Plug. The Brown Plug, and its sister the Blue Plug, are mounted to the head of the engine at the front, just under the intake manifold and next to the fuel rail.

If your temp gauge isn't doing what it should, make sure it's working properly. If you've tested it and you're still getting strange readings, make sure the cooling system is working properly.

Tachometer

The large right-hand gauge is the Tachometer. On lower-specification cars, this was replaced with a clock.

The tachometer is fed by a signal from the ECU. This black wire goes through the C101 plug to the instrument cluster, and goes to pin 7 of the blue plug (C1). However, on older vehicles (earlier than 1987) the simpler engine management system provided tachometer and fuel rate data through a separate plug, not the main loom.

The tachometer is arguably the most problematic instrument in the dash cluster, and the source of 90% of dash problems. Most of these issues can be traced to the SI batteries. If your pre-facelift car has Tachometer issues, try to locate the small three pin plug and socket above the pedal area, and ensure that it is connected properly.

If you have swapped your pre-facelift engine to a facelift, and find that your tachometer no longer works, this plug is the issue. Your new engine loom feeds the signals that went through this connector via the 20 pin C101 engine loom plug, so you have the choice of either extending two wires from the hanging plug to the engine loom socket next to the fusebox (as they are in later body looms), or teasing the two wires out of the engine loom, near the ECU plug, cutting them (abandoning the rest of the wire to the C101 plug) and splicing the plug from your old engine loom onto the wires.

Econometer

The econometer is dependent on the tachometer and the speedometer; therefore, anything that stops these two will also affect the econometer.

However, if these two are working normally but your econometer is not (especially if it reads Minimum or Maximum, but nothing in between) then the fault usually lies in the interior circuitry; the econometer is not receiving a speed signal from the speedometer. This is most likely caused by failing/ burnt out circuitry, or leaking SI batteries, and the only practical solution is to replace the dash cluster.

Dash Lights

Battery Light

The Battery Light, or Charge Indicator, is there to tell you when the Battery is being drained. Since the car battery isn't designed like other batteries, and is only really there to get the Starter motor turning, then you need to know when the car is using its electricity reserves. If the battery light comes on while you're driving, turn off the engine immediately. You can try and restart, but if the light doesn't turn off even if the engine is running, then stop the engine and perform a check of the charging system.

Oil Pressure Light

The oil pressure warning light should glow as soon as the engine is switched on, and should turn off within a second or two of the engine being cranked. If it lights up at any time while driving, then shut off the engine IMMEDIATELY.

If the oil light glows when cornering, your engine is running dangerously low on oil and requires immediate servicing.

Check Light

Some cars, specifically US and European models, were fitted with a CHECK light in the centre of the dash cluster. If a fault displayed on the check panel, then the CHECK light would flash to warn the driver of the fault. The CHECK light would stop flashing once the Check button was pressed on the check panel.

It is sometimes possible to check Motronic faults using the CHECK light. Learn more about Motronic fault codes.

Brake Lights

For those cars fitted with brake pad sensors, a flickering light is a known issue.

Indicators

Main article: Indicators

If your indicators work fine but the green dash light doesn't glow, then the most likely issue is a blown bulb for that side. If both of your indicators are at fault, the most likely issue is the hazard light switch.

Inspection Lights

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 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.

OBC

Main article: OBC

On the centre console, next to the stereo (if fitted) and above the heater controls, was the option of a Clock or an On-Board Computer (OBC). The OBC was available as a basic 6-button or an advanced 13-button instrument.

Learn more about installing your own OBC.

Check Panel

Above the rear view mirror of M20 models was a check panel, which warned the driver of any problems with lights and fluids. The check panel will show a warning light if it detects a problem with

The wiring for the check panel is an integral part of the entire car loom. To fit a check panel to cars that did not have it from the factory therefore requires the entire car loom to be placed, from the entire engine bay all the way to the rear lights, which most people consider to be impractical.

The check panel itself is driven by a number of sensors and switches inside the loom. The most problematic of these is the oil level sender. Located in the sump of the engine, it can gum up over time and constantly read low level, or it can be very specific and glow as soon as the oil level falls below maximum.

To clean the sender, remove it and soak it thoroughly in a bowl of petrol before dunking it in and out of bowl repeatedly. Before you re-install it, test it by plugging it in turned upside down and grounded on the sump; the light should go out. Then install it and see if it now works.

Extra Gauges

VDO Gauges

A desirable upgrade is to fit the three gauges from similar-period Volkswagens and Audis, which provided Oil Pressure, Oil Temperature and Voltage. These are commonly fitted below the heater controls in the central console, or in their own pod above the central air vents in the dashboard, and were available on Hartge models.

Learn more about installing VDO gauges.

Alpina

Alpina digital gauges
Alpina digital gauges

An optional extra for Alpina models was a digital gauge, fitted in place of the central air vents in the dashboard. This digital gauge gave information on Engine Oil Pressure and Temperature, Differential Temperature and Manifold Pressure. It was extremely rare even for Alpina, and was only fitted to exclusive models such as the 333i and B6 3.5S.

Common Problems

Speedo Not Working

The speedometer takes its reading from a pulse generator in the differential. This is a very simple sensor and very rarely breaks; however the plug from the sensor is exposed to the road, and the wires very often corrode and break. If your speedo isn't working, cut off the plug and 30cm of wire from the differential sensor, and replace.

The speedometer is also powered by Fuse 12, through a red/green wire which also serves the stereo. If you have worked on your stereo recently and are now having speedo problems, check this wire.

Rev Counter Not Working

When your rev counter starts playing about, it's one of the key symptoms of failing SI batteries. The giveaway will be that you can't reset your service lights either, so don't start hunting for wiring issues straight away.

However, if you have fitted new SI batteries and you're still having rev counter issues, then its worth looking fro the signal feed between the dash clocks and the ECU. The ECU pumps out a square-wave signal to the dash, so you can't check it with a regular multimeter, but you can check that the signal wire is in good condition between the clocks and the ECU. This is a black wire that, on Motronic 1.3 vehicles, runs from ECU pin 6 through the C101 plug pin 7 to the dash cluster's blue plug pin 7. Most likely, there is corrosion on the C101 plug which is affecting the signal, or the C101 isn't screwed together properly.

For older vehicles, especially those using Jetronic, there is a secondary plug next to the ECU which carries the tachometer signal to the instruments known as C104.

Fuel Gauge Not Working

Fuel gauge problems are very rarely related to the gauge itself, and are far more likely to be caused by faulty fuel senders. Learn more about the fuel level senders.

If testing the level senders works out fine, try tightening the brass nut on the rear of the fuel gauge itself. Be aware that this involves the removal of the dash cluster, so if you are doing this it is also worth assessing the condition of the SI batteries, the brake pad resistor, and the temp gauge at the same time.

Temp Gauge Not Working

The Temp Gauge is driven by the Brown Plug, a heat resistor that screws into the engine head. Failure of the brown plug is rare, so it's best to first test at the C101 plug to determine whether the fault is in the engine bay or the instrument cluster. To test, first unplug the C101 and earth pin 4 (brown/purple wire). Now if you switch the ignition on, the gauge should go to full hot. If it does, repeat the test at the brown plug by removing the cable from the brown plug, and earthing the terminal with a piece of wire (for older cars with two-pin terminals, just bridge them together). If it now works, the issue is normally corrosion of the C191 plug.

If the wire test at the C101 plug doesn't make the gauge move, the most common cause of temperature gauge issues is the Brass Nut; a small nut at the back of the dash cluster that comes loose over time. Simple tightening of this nut can resolve a number of issues, but access to this nut requires the dash cluster to be removed, which is why testing the wiring with the above method is often the preferred solution.

If you have your dash cluster removed, it is also worth investigating the condition of the SI batteries, the brake pad resistor, as well as the brass nut on the back of the fuel gauge.

Brake Pad Light Flickering

Brake pad resistor joints
Brake pad resistor joints

A very common issue relates to the Brake Pad Wear indicator, which has been known to flicker or come on at random intervals, regardless of the condition of the brake pads themselves. This problem is caused almost exclusively by a loose resistor within the dash cluster.

On the back of the cluster there is a small rectangular box moulded into the plastic near the temperature gauge. Open up the cluster, and on the circuit board, directly opposite this 'box', just clear of the temperature gauge, you will see the two soldered joints that hold a large 220 ohm resistor, housed in the box, in place. These joints have been in poor condition on every cluster, except for those that have already been resoldered.

A little bit of fresh solder and the application of a hot soldering iron, and the job's done.

If you have your dash cluster removed, it is also worth investigating the condition of the SI batteries, as well as the brass nuts on the back of the fuel gauge and temp gauge.