Tachometer Issue! S14 - 2015

[dbeiler]

Originally Posted by Zenkipowered

Friend and I tried figuring out why the tach won't get any signal. We found the yellow/red wire and the pin in the ecu and tried tapping into it directly but there was no signal. occasionally the tach would peak out at 9000 RPM then quickly go back to 0 RPMS on the tach.

The next strange thing is that there is voltage coming out of the ecu signal wire, but it reads at 14volts! which shocked me. because iirc its suppose to read from 1.5-5 volts? correct me if i am wrong.

This is confusing information. What do you consider the ECU signal wire? Clarify please.

It sounds like the tach section of the gauge cluster has finally called it quits. Thankfully, these crappy old cars have a very simple electrical system that allows for easy diagnosis with only a multimeter.

Remove the gauge cluster.

With IGN on, check for gauge operating power at Pin 21 of the M15 gauge connector.
You should be getting 12+ volts or whatever your battery voltage is.
If the rest of your gauges are working, you already know this pin is receiving power.

Check the tach ground. Check continuity from Pin 22 of the M15 gauge cluster to ground.

With the engine running, measure voltage at Pin 12 of the M15 gauge cluster. This takes the place of measuring voltage at the Yellow/Red ECU wire. If I remember correctly, 4 cylinder tachs read 1K rpm per 1 volt. You should be seeing approximately 1 volt per 1000 engine rpm. Hence, 5000 rpm should give you a 5 volt reading.

You noticed no voltage when you previously checked the Yellow/Red wire. Maybe you checked the wrong one?

If the wires check out fine, you can attempt to resolder the gauge cluster. Or just throw in it the trash and buy another one like I usually do.

[Zenkipowered]

Originally Posted by dbeiler

This is confusing information. What do you consider the ECU signal wire? Clarify please.

It sounds like the tach section of the gauge cluster has finally called it quits. Thankfully, these crappy old cars have a very simple electrical system that allows for easy diagnosis with only a multimeter.

Remove the gauge cluster.

With IGN on, check for gauge operating power at Pin 21 of the M15 gauge connector.
You should be getting 12+ volts or whatever your battery voltage is.
If the rest of your gauges are working, you already know this pin is receiving power.

Check the tach ground. Check continuity from Pin 22 of the M15 gauge cluster to ground.

With the engine running, measure voltage at Pin 12 of the M15 gauge cluster. This takes the place of measuring voltage at the Yellow/Red ECU wire. If I remember correctly, 4 cylinder tachs read 1K rpm per 1 volt. You should be seeing approximately 1 volt per 1000 engine rpm. Hence, 5000 rpm should give you a 5 volt reading.

You noticed no voltage when you previously checked the Yellow/Red wire. Maybe you checked the wrong one?

If the wires check out fine, you can attempt to resolder the gauge cluster. Or just throw in it the trash and buy another one like I usually do.

sorry, I meant the yellow / red stripe wire is what I am referring to as the tach signal wire. It has voltage but its outputting 14v. I understand it should read 1volt to read 1000rpm,but I'm worried because as mentioned its putting out 14v. I will check this again later when I get my car back as it is now in the process of being shipped to my next location.

However, Even if the OEM analog tach doesn't work that is fine because I want to use my Defi tach. However the defi tach is tapped to the wires feeding out the back of the OEM tachometer, and the defi tach doesn't work either.

So my conclusion is that there is no signal coming from the tach wire at all? but then occasionally there is and it peaks the gauge out. By peak i mean the RPM needle will go into the redline and then drop back to zero rams.


Im starting to assume that maybe a ground wire like you mentioned could be loose? or the ECU pin for the tach wire is bad? Either way I will double check and report back what I come across.

Any more ideas or things i should check for would be helpful.