Re-coding the Instrument Cluster for a shorter Service Interval display (LEDs)

[ripp222]

One topic of debate is oil change frequency. Some believe following the LED display in the Instrument Cluster allows the oil to be run too long. As such, mileage is often used to determine how frequently to change the oil. An alternative is to re-code the instrument cluster to use a shorter interval for calculating the LED display. Here is how the system works...


From BMW Service Training Literature
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SIA III
Models: E38, E39, E53, E36/5, E36/7
Production: 1996 onward excluding E36 (except E36/5 and E36/7 from 9/98)

SIA III Components:
• Instrument Cluster with LED display
• DME

Instrument Cluster (IKE, KOMBI) with LED Display
The Instrument cluster calculates the Service Interval. The cluster is also responsible for displaying the LED blocks used to represent time until next service.

DME
The DME provides the Fuel Consumption signal (ti) as the only signal used in the SIA calculation.

Principle of Operation
The sequence for displaying the necessary service is similar to SIA II. The calculation method however differs significantly.
The Instrument Cluster calculates the Service Interval based only on the input of the “ti” signal (Fuel consumed) from the DME. This method gives an accurate indication of engine load and the need for service.

The SIA data for the specific model is coded into the instrument cluster. The data consists of a Stored quantity of fuel, referred to as the “Coded Inspection Limit”. The “Coded Inspection Limit” varies according to model and can be viewed using the Diagnosis Program.
The processor of the Cluster receives the ti signal when the vehicle is used. As 20% of the stored volume is consumed one of the green LEDs will go out. Each successive 20% of fuel consumed will cause the next LED to go out until 100% of the stored value has been consumed. At this point the yellow LED comes on indicating the service that is necessary. At 108% of the volume, the red LED will illuminate indicating a service which is overdue. When the Service Interval Indicator is reset, the total stored volume of fuel is restored in the cluster and the calculation starts over again.
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As you can see, BMW uses fuel consumption to calculate the frequency of oil changes. My E53 was coded for 899 gallons of fuel as the "inspection limit coded". With mostly city driving I average between 17 & 18 MPG. Using 17.5 MGP x 899 gallons = 15,732 miles for all 5 of the GREEN LEDs to go out. That's a lot of miles. I would like a lower number. Fortunately BMW has an option to lower this "inspection limit coded" from the default of 899 gallons.

Option 988: SIA_KURZ // Coding short maintenance interval

Your BMW Dealer can add this option your ZCS (Central Coding Key). Although they might not want to for various reasons... if your Dealer gives you a confused look, tell them to review the attachments in SI B 84 01 03 CPT9000 TELEPHONE as an example of the process.
The process is a manual change of one bit for the "SA", specifically add 8 to the eighth bit in order to add Option 988 to your ZCS. My eighth bit had the number 1. Add 8 and my eighth bit becomes the number 9. My "inspection limit coded" is now 542 gallons of fuel or 9485 miles for all the GREEN LEDs to go out.

If you have rear climate control (Option 533) and 2-axle self leveling (Option 221), the you'll likely have the number 5 for the eighth bit. Add 8 to 5 and you get 13 or "D" in Hexadecimal.

If this still isn't a short enough service interval there is another option, but I haven't tried it:
Option 8ST: SIA_EXTRA_KURZ // Coding extreme short maintenance interval

Attached is a before and after photo showing my "stored value".