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A Typical 3 series Instrument
Cluster
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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
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