SI Lights

A Typical 3 series Instrument Cluster

BMW "oilservice" and "inspection" service lights were put in place in 1982 to help owners remember when to return to a service center for routine maintenance, such as oil changes and general inspection of all hoses, belts, etc.... It's actually a great idea- one that has really caught on ( Mercedes, Volvo and others are following BMWs lead)

What Causes the SII (service interval indicator) lights to come on?

The SII lights are not "event" triggered. What that means is that they are not reporting a component failure or warning of imminent failure. Rather, the SII light computer "estimates" miles traveled. Once it estimates you have gone a certain number of miles it illuminates one of the SII lights (i.e. Oilservice- 7,500 estimated miles, or Inspection-15,000 estimated miles*). Mileage is estimated based on a formula:

Technical details of the service reminder lights:

Mileage is estimated based on the following formula:

e= a(1+t+r)

e=Estimated mileage
a=Actual mileage traveled
t=1 if engine temperature is below operating temperature, else t=0
r=.5 if engine is above 4500 RPM, else r=0

Example: If you traveled 5 miles with a cold engine running at 5000 RPM, the SII computer would actually "estimate" 12.5 miles traveled:

Solving for e:

a=5 (the actual miles traveled)
t=1 (because the engine was cold)
r=.5 (the engine was exceeding 4500 RPM)

e=5 X (1+1+.5)=12.5 estimated miles (from a trip of only 5 miles)

Once the computer reaches a certain count value (about 7,500 miles for Oilservice and 15,000 miles for inspection*), it will illuminate one of the service lights (oilservice or inspection) seen below.

The five green "countdown" lights are there to let you know approximately how long it will be before the next time your Oilservice or Inspection light will come on.

Explained:

Say an Oilservice or Inspection is due in 3000 miles, and
There are three green lights remaining (they shut off within 15 seconds of starting your engine)

So; 3000 miles remaining divided by 3 green leds = 1000 miles per Green led.

The yellow light along with the word Oilservice/Inspection indicates service is now due. The red lights indicate service overdue by approximately 100 miles per light.

*Varies with year and model