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How to Change E30 Service Indicator (SI) Batteries.

It is no secret that the E30 is now an old car. With the first models coming out in 1982, now in 2022 these elder e30s have had their 40th birthday! With that age comes inevitable electrical gremlins and today, we are going to show you how to fix one of them yourself, the “Service Indicator” or SI board batteries.

First let’s begin with what the SI batteries are and how they work. The story begins with the SI board.

The SI board is the main electrical board inside of your E30 cluster. It has lots of functions including but not limited to…

1. Tachometer

2. Coolant Temperature

3. LED SI Indicator

On this board are several integrated circuits that perform translations of the signal from various sensors in the vehicle to the data that you read off the cluster.

So, what do the SI batteries have to do with all this? Simple, the SI batteries store the service information when the car loses power as well as help to power some of the integrated circuits while the vehicle is running. If the batteries go bad, they will no longer be able to distribute power properly to the board to perform its essential functions.

This brings us directly to some symptoms of bad SI board batteries.

1. Tachometer not working

2. Coolant gauge not working

3. SI indicator not working (should illuminate on key on)

So now that you know what is going on, I will now walk you through step by step how to change your batteries.

1. Remove the Gauge Cluster

Here is a link to a great DIY from Classic Bimmer Bits that will walk you through step by step if you don’t know how to do this already.

2. Unscrew Gold Colored Phillips Screws on the Back of the Cluster

Remove all the gold colored screws from the outer edges of the cluster and the one in the middle of the cluster above the check control bulb.

3. Separate the Cluster into its Two Halves

Carefully separate the cluster, you should not have to pull very hard. There are pins that connect the SI board to the cluster board that will need to slide out. Be careful not to bend or snap them!

4. Remove the Check Control Cover

The check control cover is held in by a single phillips screw, remove that then pull the cover out of the front of the cluster.

5. Remove the “Cylinder encoder”

From the front side of the cluster, pull the cluster encoder out of the SI board. This board contains an integrated circuit that translates the RPM signal to a signal that can be used by your tach. The ones found in a 4 cylinder E30 will be different than in a 6 cylinder e30.

6. Pull Out the SI Board

Pulling on the left most and right most ends of the board pull directly out to remove the SI board from the front half of the cluster.

7. Inspect your SI batteries

E30s have two main kinds of SI batteries, for simplicity we will call them “small version” and “big version''.

Small Version:


Big Version:


Before we begin removing the batteries from the board, it is a good idea to check their voltage.

Measure the voltage on each of the individual batteries. They should read the following

Small: 3.2v

Large: 1.5v

If you are reading something much lower, then they probably need to be changed. We had .59v on these when we did this board for a customer.

8. De-solder your SI board Batteries

There are six tabs that hold the batteries to the board, two on the positive terminal and one on the negative for each battery. It is easy to identify the right locations on the back of the board because they have the largest solder connections in the area.

Use a variable heat soldering iron, and use the minimum heat that will still melt the solder. Once it is melted, use solder wick, and or a solder vacuum to remove all the solder from each of the six joints.

9. Bend the Battery Tabs up

Once the solder is removed, you should be able to bend the terminals of the batteries up so they can come out of the board. If you can’t, you probably need to remove more solder from the joints.

10. Remove the Old SI Batteries

Now the batteries should come out very easily, just be careful not to damage any of the nearby components. Once the batteries are out, your board should look like this!

11. Place the New Batteries Into the Board.

Insert the terminals of the batteries into the board, they can only go in one way due to having two pins on one side and only one on the other.

Flip the board over and bend the ends of the batteries to a 90 degree angle, parallel with the surface of the board, just like the original ones were.

12. Solder the New SI Batteries to the Board.

Using the same heat setting as you used to remove the old batteries, re-solder the six connections on the back of the board using electronics board grade solder.

13. Reassemble and Test

The hard work is done! Reassemble the cluster, then install it back into your car! Key on the car and check for SI lights. Then turn on the car and check for tachometer and coolant temperature. Congrats! You have successfully fixed your SI batteries!

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