E30 Zone

I have an m42 and my tach isn't working.
After checking by replacing the coding plug, working dash cluster,check Ed all fuses and signal path. There is no rpm signal to the dash from pin 74.

Could a faulty crank sensor cause the problem?

Will my engine still run without a working cps?

The car starts and drives perfectly fine what could be the reason for no signal?

Engine cannot run without a fully working CPS. It's the one sensor that is critical to the engine running.
More modern engines have a cam position sensor as well, which some ECUs can substitute for the crank signal to provide a 'get you home' limp mode, but nothing anything like as sophisticated as that with a M42.
If you are sure that you have a working cluster, with good SI board batteries, then that narrows it down to the ECU, which would be very unusual, or the wiring between them.
Check that the C101 engine loom plug and socket are fitted together with the lock ring fully home. This was the problem/solution for me on one occasion.

Thanks Brian, I have tried that with no luck should there be voltage across pin 9 and ground of the c101 female side when the lid is off?

Anyway to test continuity between the engine and engine side of c101 vs the dash side?

I also have continuity between pin 7 (black wire) of the blue plug and pin 74 on the ecu plug.

After trying a few things with help from Rich (Rix313) I have tested the continuity between ECU pin 74 and Tach plug (blue one behind dash) pin 7.
there is continuity and a variable voltage RPM signal coming trough.

Does this mean that there is an earthing problem in the plug?
Does anyone have a pinout for the blue plug / dash cluster or a way for me to test this?

I was thinking of running a new earth from the tach directly to ground and seeing if the tach works that way.

Would this be a good idea or will it damage my clocks even more?

Circuit diagram here: http://www.autolib.diakom.ru/CAR/BMW/19 ... /fig08.pdf
I thought you said that you have a known good cluster? All of the electronics for the tacho. are on the SI board, and the first thing I'd check for a non working one is the condition of the SI boar batteries.
Not quite sure what you mean by a "new earth for the tacho." The instrument itself is just a meter, which connects directly, via two plugs and sockets, to the SI board. There's no earth just for the tacho. to bypass.

Yes my cluster worked fine in a friends E30. So we know the cluster and si board is good. Also the black wire for rpm signal under the blue plug gives a variable voltage when I rev the engine. I also took a known good cluster and tested it in my car with the same no tacho result.


I was thinking that the problem could be to do with the connection in the plugs.

These are my test results for the RPM signal

Turns out my tach is outputting around 3v according to this post on R3V it should be more like 8v

Post link: https://www.r3vlimited.com/board/forum/ ... -fuel-temp

Can anyone verify this?

Full post here because it's good:

E30 Cluster diagnostics and testing information.

Requirements - basic electronics understanding, being able to read ETM schematics, using DMM meter, having a bench power supply and signal generator at minimum.

E30 clusters as we all know can be a problem area, due to variety of reasons…what I’l concentrate on here is how you can test most functions of the cluster yourself with basic electronics knowledge. There are no high voltages here, so there is little risk to hurt yourself but as with anything else if you don’t feel comfortable with electronics then don’t attempt to mess with it or seek help.

I got tired one day of having to remove the cluster out of my car in order to test a spare cluster or SI board for myself or a local e30 owner. For the longest time I’ve wanted to figure out how to test most common functions or issues on the bench. I’ve already had most of the tools needed, so it was just a matter of finding time to do this.

First thing you should do is get familiar with reading basic schematics as outlined in the ETM you can find online.
Section 6210 is what you’ll need to look for. This shows the cluster diagrams and connections for various sensors and switches.

We’ll start with the basics, at the back of the cluster you have a C1 and C2 connectors, these are the normally WHITE and BLUE can also be different shade if the main board was replaced. C1 (white) is on the TEMP gauge side (right side) and the C2 (blue) is on the FUEL gauge side (left side).

The diagram in the ETM shows pins, along with wire colors and markings if these are on the C1 or C2 side , there are other connectors as well such as C3 which is the yellow connector for OBC but that’s for another day.

What you need to do next is look at what wires on C1 and C2 are for Power and Ground first, you’ll use these to supply power to the cluster using a bench power supply . Cluster does not take a lot of current, so something with 12-13 volts and 1amp of current will be enough.

As an example, C1 has pin 14 (wire code GN) that goes to positive side via power distribution block.
On C1 you also have pin 20 (brown) that goes to ground.

C2 connector has pin 13 (VI wire) that goes to power thats ON when in ACC, Run or Start modes.
and Pin 16 (BR) that goes to ground.

Take note of C2 pin 12, this should be BR/RD wire that connects to the Speedometer via it’s PCB pin 31b. This is the SPEED INPUT connector we’ll need in order to test the Speedometer/Odometer.

For our TEMP gauge we need to look for PIN 26 on the C1 side, this can be BR/VI color and goes to the engine temp sender for our cluster. The other side is grounded.

For our FUEL gauge we need to look for PIN 4 on the C2 side. This side goes to the fuel level sender, if your car has TWO of these they are connected in SERIES…so if one sender is bad or faulty it will have a negative effect on the circuit. Think of old christmas lights, where one light goes out and the whole thing is off. Pin 5 on the C2 side goes to the ON/OFF switch (float) thats inside the Fuel level sender…this simply grounds the circuit to light up the LOW FUEL light. So you can test your instrument cluster LOW FUEL light by simply grounding the C2 pin 5.

Service Interval (SI Board) lights can be reset via the Pin 22 on the C1 side. This pin goes to the diagnostics port that we are all familiar with, you simply need to ground Pin 22 to ground in order to reset the light(s).

Tachometer gets it’s signal via the Pin 7 on the C1 connector, it should be a Black wire. The MPG gauge get’s it’s signal from the C1 pin 11 YL/WT wire.

You can obviously look up the pins and wires needed to trigger your LEFT/RIGHT or Emergency Flasher lights, some of these are grounded and some are connected to power, but it’s easy to follow the diagram to tell. For example the High Beam light is on pin 12 of the C1 connector and you need to connect it to power, as the other side is connected to ground via C2 pin 15 , C1 pin 20. But the OIL pressure warning switch is connected to power , but the other side is grounded via a OIL pressure switch via PIN 18 on the C1 side.

Now that we got the basics out of the way, let’s move onto testing the gauges. The easiest gauge to test is the Temp Gauge , followed by the Fuel, Speedo, Tach.

The temp and fuel gauges are connected in series with voltage, the needle on the gauge is calibrated to change it’s position based on sender it’s connected to. The Temp gauge sender that’s on the engine is a variable resistor that changes it’s value based on the temperature. The fuel gauge is likewise get’s it’s signal from the fuel sender (or senders if you have two they are connected in SERIES), it’s basically a Variable Resistor (potentiometer).

What you can do is replace the temp sender and fuel sender with variable resistors (0-250 ohms for example) , you connect the center leg of the variable resistor to PiN 4 on C2 side of the cluster to test the Fuel Gauge, likewise you’d connect the center leg of the variable resistor to PIN 26 on the C1 side of the cluster to test the Temp Gauge.

As an example, 1/2 mark on the temp gauge in my testing shows when the Temp Sender is about 50 ohms . You can also purchase a fixed value resistor and use that to quickly test if your gauge works or if it’s the sender that’s faulty and not sending any value by disconnecting the sender harness under your hood and simply connecting a resistor in place of the Temp Sender Unit . One pin goes to the harness, and the other pin goes to ground. This should trigger your temp gauge…if it does not then you can do the same test utilizing the PIN 26 on the C1 side or check connectivity between the above C1 PIn26 pin and the harness end. In my finding 145-115 ohms is the BLUE area, 51-35 is the 3/4 area and 25ohms and less is RED.

Now, let’s move onto the Speedometer / Odometer. I am using a MotoMeter unit here as an example. The speedometer/odometer unit has 4 pins, +, A, 31b and 31. If you look at the ETM you’ll learn that 31b is signal input, 31 is ground, + is for positive power (A looks like is for OBC) You can supply 12 volts power to the speedometer / odometer outside of the cluster for testing . You’ll need a signal generator that can send Square Wave signal of around 9-10 volts of variable frequency. 20mph is shown when the signal is of 0.043Khz, 40mph is 0.080khz, 60mph is 0.127khz (127hz), 80mph is 166hz, 100mph is 205hz, 120mph is 244hz, 140mph is 286hz as an example from my testing. I’ve noticed that you need about 9volts for the speedometer to trigger, vs. tach needing only 8+

You can send the square wave signal either directly to the speedometer unit pin 31b , OR if you are testing it w/o removing it from the cluster then it would go to PIN 12 of C2 connector (goes to the differential sender).

Tachometer, get’s it’s signal from Pin 7 of C1 connector. Engine speed is also a Square Wave signal, I’ve noticed 8volts is the minimum that gets it’s moving. The frequency vs RPM as an example is the following

500rpm is about 0.034 kHz
1000rpm is about 0.058 kHz
2000rpm is 0.105 kHz or 105 hz
3000rpm is 152 hz
4000rpm is 200hz
5000rpm is 249hz
6000rpm is 301hz
7000rpm is 348hz

There are many ways you can generate the signal, either by purchasing a bench signal generator or by building your own circuit using any number of kits available online and eBay. Signal generators aren’t expensive or complicated to build, just ensure you get one that can output Square Wave vs Sine Wave and high enough voltage (these are usually also variable).

I know it’s a long post, but this should get you going with getting the basics squared . With the information above, simple tools and understanding the schematics and wiring you should be able to at the very least troubleshoot where the issue is…. is it the cluster that’s not getting the signal (bad senders, bad wiring, short etc) or is it the gauge(s) cluster that’s faulty .E30 Cluster diagnostics and testing information.

Requirements - basic electronics understanding, being able to read ETM schematics, using DMM meter, having a bench power supply and signal generator at minimum.

E30 clusters as we all know can be a problem area, due to variety of reasons…what I’l concentrate on here is how you can test most functions of the cluster yourself with basic electronics knowledge. There are no high voltages here, so there is little risk to hurt yourself but as with anything else if you don’t feel comfortable with electronics then don’t attempt to mess with it or seek help.

I got tired one day of having to remove the cluster out of my car in order to test a spare cluster or SI board for myself or a local e30 owner. For the longest time I’ve wanted to figure out how to test most common functions or issues on the bench. I’ve already had most of the tools needed, so it was just a matter of finding time to do this.

First thing you should do is get familiar with reading basic schematics as outlined in the ETM you can find online.
Section 6210 is what you’ll need to look for. This shows the cluster diagrams and connections for various sensors and switches.

We’ll start with the basics, at the back of the cluster you have a C1 and C2 connectors, these are the normally WHITE and BLUE can also be different shade if the main board was replaced. C1 (white) is on the TEMP gauge side (right side) and the C2 (blue) is on the FUEL gauge side (left side).

The diagram in the ETM shows pins, along with wire colors and markings if these are on the C1 or C2 side , there are other connectors as well such as C3 which is the yellow connector for OBC but that’s for another day.

What you need to do next is look at what wires on C1 and C2 are for Power and Ground first, you’ll use these to supply power to the cluster using a bench power supply . Cluster does not take a lot of current, so something with 12-13 volts and 1amp of current will be enough.

As an example, C1 has pin 14 (wire code GN) that goes to positive side via power distribution block.
On C1 you also have pin 20 (brown) that goes to ground.

C2 connector has pin 13 (VI wire) that goes to power thats ON when in ACC, Run or Start modes.
and Pin 16 (BR) that goes to ground.

Take note of C2 pin 12, this should be BR/RD wire that connects to the Speedometer via it’s PCB pin 31b. This is the SPEED INPUT connector we’ll need in order to test the Speedometer/Odometer.

For our TEMP gauge we need to look for PIN 26 on the C1 side, this can be BR/VI color and goes to the engine temp sender for our cluster. The other side is grounded.

For our FUEL gauge we need to look for PIN 4 on the C2 side. This side goes to the fuel level sender, if your car has TWO of these they are connected in SERIES…so if one sender is bad or faulty it will have a negative effect on the circuit. Think of old christmas lights, where one light goes out and the whole thing is off. Pin 5 on the C2 side goes to the ON/OFF switch (float) thats inside the Fuel level sender…this simply grounds the circuit to light up the LOW FUEL light. So you can test your instrument cluster LOW FUEL light by simply grounding the C2 pin 5.

Service Interval (SI Board) lights can be reset via the Pin 22 on the C1 side. This pin goes to the diagnostics port that we are all familiar with, you simply need to ground Pin 22 to ground in order to reset the light(s).

Tachometer gets it’s signal via the Pin 7 on the C1 connector, it should be a Black wire. The MPG gauge get’s it’s signal from the C1 pin 11 YL/WT wire.

You can obviously look up the pins and wires needed to trigger your LEFT/RIGHT or Emergency Flasher lights, some of these are grounded and some are connected to power, but it’s easy to follow the diagram to tell. For example the High Beam light is on pin 12 of the C1 connector and you need to connect it to power, as the other side is connected to ground via C2 pin 15 , C1 pin 20. But the OIL pressure warning switch is connected to power , but the other side is grounded via a OIL pressure switch via PIN 18 on the C1 side.

Now that we got the basics out of the way, let’s move onto testing the gauges. The easiest gauge to test is the Temp Gauge , followed by the Fuel, Speedo, Tach.

The temp and fuel gauges are connected in series with voltage, the needle on the gauge is calibrated to change it’s position based on sender it’s connected to. The Temp gauge sender that’s on the engine is a variable resistor that changes it’s value based on the temperature. The fuel gauge is likewise get’s it’s signal from the fuel sender (or senders if you have two they are connected in SERIES), it’s basically a Variable Resistor (potentiometer).

What you can do is replace the temp sender and fuel sender with variable resistors (0-250 ohms for example) , you connect the center leg of the variable resistor to PiN 4 on C2 side of the cluster to test the Fuel Gauge, likewise you’d connect the center leg of the variable resistor to PIN 26 on the C1 side of the cluster to test the Temp Gauge.

As an example, 1/2 mark on the temp gauge in my testing shows when the Temp Sender is about 50 ohms . You can also purchase a fixed value resistor and use that to quickly test if your gauge works or if it’s the sender that’s faulty and not sending any value by disconnecting the sender harness under your hood and simply connecting a resistor in place of the Temp Sender Unit . One pin goes to the harness, and the other pin goes to ground. This should trigger your temp gauge…if it does not then you can do the same test utilizing the PIN 26 on the C1 side or check connectivity between the above C1 PIn26 pin and the harness end. In my finding 145-115 ohms is the BLUE area, 51-35 is the 3/4 area and 25ohms and less is RED.

Now, let’s move onto the Speedometer / Odometer. I am using a MotoMeter unit here as an example. The speedometer/odometer unit has 4 pins, +, A, 31b and 31. If you look at the ETM you’ll learn that 31b is signal input, 31 is ground, + is for positive power (A looks like is for OBC) You can supply 12 volts power to the speedometer / odometer outside of the cluster for testing . You’ll need a signal generator that can send Square Wave signal of around 9-10 volts of variable frequency. 20mph is shown when the signal is of 0.043Khz, 40mph is 0.080khz, 60mph is 0.127khz (127hz), 80mph is 166hz, 100mph is 205hz, 120mph is 244hz, 140mph is 286hz as an example from my testing. I’ve noticed that you need about 9volts for the speedometer to trigger, vs. tach needing only 8+

You can send the square wave signal either directly to the speedometer unit pin 31b , OR if you are testing it w/o removing it from the cluster then it would go to PIN 12 of C2 connector (goes to the differential sender).

Tachometer, get’s it’s signal from Pin 7 of C1 connector. Engine speed is also a Square Wave signal, I’ve noticed 8volts is the minimum that gets it’s moving. The frequency vs RPM as an example is the following

500rpm is about 0.034 kHz
1000rpm is about 0.058 kHz
2000rpm is 0.105 kHz or 105 hz
3000rpm is 152 hz
4000rpm is 200hz
5000rpm is 249hz
6000rpm is 301hz
7000rpm is 348hz

There are many ways you can generate the signal, either by purchasing a bench signal generator or by building your own circuit using any number of kits available online and eBay. Signal generators aren’t expensive or complicated to build, just ensure you get one that can output Square Wave vs Sine Wave and high enough voltage (these are usually also variable).

I know it’s a long post, but this should get you going with getting the basics squared . With the information above, simple tools and understanding the schematics and wiring you should be able to at the very least troubleshoot where the issue is…. is it the cluster that’s not getting the signal (bad senders, bad wiring, short etc) or is it the gauge(s) cluster that’s faulty .