Tach and MPG do not function

[Zinno28]

'87 535is M30B34 242k Miles. My 7k tach and MPG have not worked since i bought the car. Fuses are good. (Just did the Holy Grail swap). Checked the DME and no visible signs of solder issues. I have replaced the reference and speed sensor. Is there supposed to be a wire to the coil like on 2002's or no ? Tach gets a signal from the computer right ? My coding plug is 1377665 #14 - the tabs are broken off on it but it fits in fine, is there a way to test the plug ? Can the coding plug be bad ? What am I missing ? Scratching my head. Just want the tach to work....

[turbodan]

It's almost guaranteed to be a cluster issue, but there is one possibility that I can think of. The tach and econometer get their signal through the C103 connector in the glove box. The ignition also sends a 12v signal through here to wake the DME up, so if the car runs it's probably plugged in.

Its a white, five pin straight connector if I remember correctly. Branches out of the engine harness near the DME plug and connects to it's counterpart in the dash harness.

Other than that, make sure you have all of the connections at the cluster hooked up. The little blue, green and white plugs are easy to overlook. I don't know if that would cause this issue though.

[Zinno28]

Thanks turbodan ! 

I checked my C103 and it appears to have 3 wires coming in and five going out (or vice versa). See pic
 

Is this how it's supposed to be or has someone been messing around in here ?

[Zinno28]

Also ! 
I don't have a Green, Blue and White in the back of my cluster.... Just these below. A blue/white stripe. A yellow/red stripe and a Blue/ Yellow stripe X2 with a blue/brown stripe. I'm confused now 
 

 

[turbodan]

Not all cars have all three. I think the green one is from the OBC harness. The white and blue are pictured. 

You'll have to pull up the ETM and see which wires are for what in your application. The tach and fuel consumption definitely go through that connector. I dont know which wires are which from memory though.

[///M]

With issues with the tach and speedo the most likely problem is with the Service indicator (SI) board in the cluster. The batteries can leak and damage the board resulting in  problems. The tach and speedo are routed thought the SI board.
Do the SI lights work? The board can be bypassed or you can buy a replacement board that replaces the one that is there.
The SI function no longer works but if it does not work now you may not be concerned.
BMW E28 E23 E24 Batteryless SI Board ( Instrument Cluster Repair Fix Solution ) 62111394270 - Ivo Christov BMW E28 specialist

[Zinno28]

Thanks ///M ! I replaced the SI batteries about 6 months ago and the SI works great  

Is there a way to test the Coding plug ? Shouldn't there be 5 wires in and out of C103 ? 

[///M]

The C103 is different for other models like e30 could be 3 pin or e24 had 4 pin. The one you have in the picture has the same three wires connected.
You can check the at the connector for voltage with a meter. The Black/blue wire is from the DME it connects to the black wire which is the engine speed signal to the tachometer.
With the engine running connect a probe to the black wire and the other to a ground on the chassis. You should show a voltage it will not be 12 volts as it is a frequency.
If there is then the next place to check is pin 8 on the blue 26 pin connector. You could check here first as this is where the signal connects to the cluster.
On the cluster the pin numbers are marked. The Blue plug also has the pins marked but they you have to remove the blue cover to see them.

Check what numbers are on the coding plug it may not be correct as they are connected to tachometer function.

[turbodan]

Interesting that only three are present.  I combed the ETM out of curiosity and it appears that is correct for the 88 535.  Pin 4 with the green/yellow wire is unused.  It originates from the A/C control circuit but does not reach the DME as it terminates at the C103.  Pin 5 with the green/red originates from a 32 degree temp switch but also terminates at the C103.

You do have 1, 2 and 3 accounted for, as you would expect for a stock 535.

I'm still thinking this is a cluster problem.

[Zinno28]

Big thanks to both of you!

I was able to get a frequency reading with a voltmeter from C103 and #8 on the blue plug. 

I'm attaching pics of the back of my cluster. It appears the backing is from a 1995- judging by the stickers? Also, where I plug the Green, Blue and White connectors into the back, only one (the blue) has conductive material on it. White and green are just the circuit board material. See pic.
BMW 14 1377665 is the correct coding plug. Any further ideas ? 


 


 


 

 

[Mike W.]

Big thanks to both of you!

I was able to get a frequency reading with a voltmeter from C103 and #8 on the blue plug. 

I'm attaching pics of the back of my cluster. It appears the backing is from a 1995- judging by the stickers? Also, where I plug the Green, Blue and White connectors into the back, only one (the blue) has conductive material on it. White and green are just the circuit board material. See pic.
BMW 14 1377665 is the correct coding plug. Any further ideas ? 
 

I left out the coding plug one time and the tach worked, the MPG meter and OBC readings worked, but were way off. FWIW.

In case you're not aware, and you probably are, those little plugs plug in backwards to the direction I think they should. The wires point towards the cluster, not way from it.

[///M]

A number of points on your issue. Someone has been there before. The speedometer does not match the cluster housing not just colour but the date stamp. The cluster housing is 95 so must have been a replacement. Someone maybe swapped in a different speedometer to try to fix the problem.

The circuit board without the conductive material visible on the "Brun" is normal.

As you have a frequency at pin 8 means the issue is in the cluster. As I said the  problems you have are a symptom of SI board problems number one being the leaking batteries. The signal goes through the SI board processor.
The last clusters had no rechargeable batteries but long lasting lithium unlike previous ones. The older cluster has a 15 pin connector with a ribbon cable pin 4 is the tachometer.

Pin 8 connects to the SI board pin 4 in the cluster so if you have a frequency reading there then the problem is the processor or the connection to the tachometer. There is a resistor in the circuit which could have burnt out.
If you open the cluster you can work back from the tachometer.
It would be good to see a picture of the board to see which type it is.

With regard to the coding plug. The E28 came in different flavors for different markets just like the word flavour The coding plug meant that you would get what was relevant to your car.
4 or 6 cylinder, petrol or diesel, fuel economy, maximum rpm are controlled by bridging circuits.

[Zinno28]

Huge help ///M ! 

Ok, it appears my circuit board is from 1995. There are date stamps on different circuits. So, moving forward, what would you fine folks recommend ? Should I swap the board out for an '87 and possibly assign an SI delete board from Mr Ivo ? (I don't really care about the SI indicators) It doesn't seem I'll be able to get my tach to work with this set up as it is with this mixture of board and instruments.

Again , thanks for all your help ! 
 


 

 

[Mike W.]

Other than substitution I'm not sure how you'd test, but everyone is focused on the board. I wonder if it's not just the tach assy that's bad? IIRC and it's been a while since I've been into one, but do all the pins line up between the tach and the board? What's the date code on the tach?

One other thing, I'm not sure of the changeover date between early and late SI boards, but I'm not sure late boards with the lithium batteries are problematic like the earlier NiCads. Actually I doubt it, but I'm not sure.

[Zinno28]

Thanks Mike W !

Yes, the pins line up. 2/87 is the date code on the tach. 

[Aldo525]

Circuit plate looks like mine ('87 525i), I mean late cluster (they start 02/86) so it is the right part for your car regardless of whether it is from 95, they were built well into the 90s as replacements.


Are you sure that part of circuit are ok not broken???....Any chance you can get a borrowed tachometer and try it?
 

 

[///M]

That is a later board with the non rechargeable batteries. Should be fitted to cars from 9/86 on. The circuit is different than earlier cars and does not have the 15 pin ribbon cable I mentioned.
The next step is to check for signal at the tachometer. Do you have a picture of the tachometer connections on the rear? The issue is the tachometer or the connection to it.
It goes through the SI processor as I said so does the speed signal to the speedometer, but one issue at a time. The SI processor can be bypassed if it is the problem.

[Zinno28]

Thanks again ///M and Aldo !
Here's pictures of the back of tach:

 


 


 
Everything appears fine. No obvious trauma. Can I bench test the tach somehow ?
 

[Aldo525]

Your cluster looks like new to me....I found this e30' tacho testing, not sure about the circuits difference but maybe it's useful.

https://www.instructables.com/Bench-Tes ... achometer/

[Zinno28]

Thanks Aldo! Unfortunately, I don't have a function generator. 

[Aldo525]

Thanks Aldo! Unfortunately, I don't have a function generator. 

In the description says "If your SI battery is dead, your tachometer will not work. However, contrary to popular belief, you don't need to replace the battery. You only need to remove the dead batteries and the tachometer will work again. Dead batteries seem to draw electrical current and leave too little to operate the tach."

Did you test your batteries??

[Zinno28]

Aldo- Yes- I replaced the SI batteries about 6 months ago. Maybe take them out and see what happens?

[Aldo525]

Aldo- Yes- I replaced the SI batteries about 6 months ago. Maybe take them out and see what happens?

Maybe not remove them but at least test that they have sufficient voltage at the ends and, if possible, at distant points on the same circuit to prove that the welds were well done.

[///M]

Had a look at some clusters. I have one of the same vintage. Tested and found the same problem with the tachometer no working so I removed it and connected as in the photo. I used a signal generator and it works but will not work in the board it appears that there is a voltage drop in the circuit will need further investigation.
If you want to test your tachometer you may find that it works. To test connect pin 5 to ground of the car and connect pin 8 of the blue connector on the cluster wiring harness. Start the car and you will have the full 12 volt signal at the tachometer. This will  bypass the board completely but before that you could check the frequency and voltage of the signal. There is a resistor (12K ohms) on the board which drops the current there are also some other resistors which are acting to drop the signal to low to power the tachometer on my board.
I would be careful not to short the pins as they are close. I insulated both pins. 
Only do this if you are comfortable with information you get from a person on the internet.
 

 

[Zinno28]

I took the information from the person on the internet and ran with it! No luck. I grounded #5 to the car and connected #6 in the tach to #8 on the blue plug. Nothing happened. So, tach is not functional (at least with this test.) Am I in the market for another tach or another circuit board? Or maybe that voltage drop resistor failed ? Also ! I removed the batteries for the SI board and all the green lights still light up along with "inspection" when I start the car.  Hmmmmm

Thanks ///M and Aldo!

[///M]

Did you check the frequency and voltage at the connections to the tachometer in the picture? You should see around 40Hz at idle and 6-8volts. The tachometer is separate and only the two wires connected to it.
If you have both readings then the tachometer is not working as you are getting the signal but the unit is not functioning. Increasing rpm should show an increase in frequency.
Next step a replacement tachometer you can check it before installing. 
If the car came without a working speedometer and tachometer there could be other problems with the cluster.
To check the speed signal to the speedometer you can connect the all the plugs except the 26 pin yellow. On the yellow of the cluster connect pin 3 or 16 ground and pin 8 or 21 speed signal from speedometer. Pin 8 is the early so check both.
You have to have the rear wheels of the ground (not just a jack) and have the car driving in gear increasing speed increasing frequency on the meter.
Again be wary of advice given on the internet.  

Its  not glasses I need its eyes. Just realized MPG why I thought the issue was SI problems.

[Zinno28]

Thanks ///M !

I just installed a crack free dash so I haven't worked on the tach issue in a bit. 

Still don't know how my SI lights work with no batteries installed . How is that possible ? 

[///M]

The batteries are only a memory backup for loss of the permanent 12v supply. If you had two green lights showing and cut the 12v supply then the batteries are used to continue with the two green lights or whatever the setting is just like in a mains clock with battery back up. 

[Zinno28]

Well, I sourced (eBay) and installed a supposedly tested tachometer - still does not work. Grrrrr. Not sure what to do aside from bring it in to a shop. 

[///M]

Well one of you is wrong! If the seller is correct then you are not testing it correctly. If you are testing correctly then the unit does not work. As I said in the previous post check the voltage and the frequency of the signal from the DME at the cluster and note the results.
The tachometer needs sufficient voltage to work. The frequency gives the reading on the dial.