Instruments

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.

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.

Individual Gauges

Speedometer

The Speedometer is a very quick way of seeing which engine is fitted to your car.

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.

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

The same fuel gauge was fitted to all models of E30, and features a simple swing gauge as well as an amber warning lamp, which illuminates when the tank reaches its last 8 litres.

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|fuel system.

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, presumably, 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 it 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.

Failure of the brown plug is rare, but not uncommon. To test, first unplug the cable from the brown plug, and join the two terminals with a piece of wire. If you switch the ignition on, the gauge should go to full hot. If it doesn't, reconnect the cable and repeat the test by earthing pin 4 (brown/purple wire) of the C101 plug. If it now works, the issue is normally corrosion of the C191 plug.

If the wire test at the C101 plug still 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 first is the preferred solution.

Tachometer

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.

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. 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.

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

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

Main article: Resetting the Inspection lights.

If your Inspection lights constantly glow, even after being reset, this is usually a fault of the SI batteries.

OBC

Main article: 13-button 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.

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.