Si Board Info

Si (service interval) board problems: pre-1990 BMWs (NiCad Batteries)

(Note: The subject of this page has nothing to do with our tools- the reset/scan tool does not require batteries.)

By far the most common problem with the BMW service lights, and instrument cluster in general, is the si board: a printed circuit board located inside the cars instrument housing which controls, among other things, the operation of your service interval lights. The Si board is what decides how often your Si lights come on. It is a simple computer which monitors your driving conditions and keeps tabs on how far you've gone and how well you have behaved in respect to RPM and engine temp. In order for it to remember this accumulated "tab" while the engine is starting (a time in which it is starved of power; as all power is directed to starting the engine) it must have a back up power source, just like the "CMOS" batteries in a typical PC. Batteries, as you know, eventually die. In the case of the typical BMW si board batteries, one should expect a battery life span of no more than five years- little as two, as much as eight years. It depends on your local average climate (We sell a lot of batteries into Florida, Arizona etc...).

SYMPTOMS: Depending on the model of the BMW, a dead Si board can cause other problems such as erratic gauges. But the most common symptom of Si battery failure is the appearance of the "Inspection" light shortly after a reset- It could be just a few minutes, or even a day later. Other indications include non-response to a reset, lights stay on while car is off with no key in the ignition, lights never come on, improper green-yellow-red led sequence in respect to the Oilservice and Inspection intervals, si light flashing, and on certain models, gauge problems.

REPLACEMENT PROCEDURE: Replacing your Si batteries is not particularly difficult, but it is time consuming (90-180 minutes). It requires that you have a soldering iron and basic hand tools, and more importantly, you know how to use them. The majority of the time to do the job is consumed in removing the instrument cluster and dismantling it, especially on the 3 series. Fortunately, steering wheel removal is not necessary on most models. Our Si battery replacement kit includes instruction on doing the procedure, though one should note that the photographic and procedural subjects in our replacement battery kit ($24.95 part number SIBN) consist of a 1984 318i, a 1985 528e, and a 1986 635csi, so you, depending on the year and model of your BMW, may have to improvise.

IF YOUR CAR HAS AN AIRBAG: Unfortunately, there is no SI battery replacement kit available for SRS (airbag) equipped cars.

BAD PC BOARD: It happens. Sometimes you just need a new board. Contact ECMS for replacement PCB's and control modules for your BMW at a savings over the cost of a new factory "fresh" board. They can be reached at (570) 883 9930, or 1-800-687-3267, please tell them we sent you.