ECU & ECU check light questions...

[tomm]

Hi

I want to sort out an engine check light at pin 15 of the ECU (as previously suggested by Brian Moore) to try and display the ECU error codes (on an '87 320i)

1. Where is the ECU?

2. If this the right pin diagram?



3. If it is, is the diagram oriented as if you are looking at the pins from the wire side or from the plug side?

4. One side does to pin 15, but where should I connect the other side of the light to?


Thanks

[dazleeds]

ecu is under sterring wheel to the right

[Speedtouch]

ECU is located above the driver's knees (remove the lower dashboard cover to reveal the silver box, which will have 'Motronic' written on it.

[Speedtouch]

Mind you, an '87 320i may also have Bosch L-Jetronic, in which case the ECU won't have 'Motronic' written on it!

[tomm]

I think I've got the Motronic version

[Brianmoooore]

Pin 15 is correct. The pin numbers are written on the ECU at the end of the rows in very small figures.
Other side of the lamp goes to the green/white (fused) switched ignition 12V+.
I've only done this with M50 ECUs. I've no idea if it works with UK spec E30 ECUs.

[tomm]

Other side of the lamp goes to the green/white (fused) switched ignition 12V+

Is this at the ECU, or elsewhere, Brian?

I've only done this with M50 ECUs. I've no idea if it works with UK spec E30 ECUs.

I'll report back ;)

[Speedtouch]

Fault codes are here dude:

http://member.rivernet.com.au/btaylor/B ... Codes.html

Let us know how you get on...I'm itching to try this on mine

[Brianmoooore]

Other side of the lamp goes to the green/white (fused) switched ignition 12V+

Is this at the ECU, or elsewhere, Brian?

Anywhere you can pick it up. It's at pins B6 and A23 of the instrument cluster.

[tomm]

So I'll have to dismantle the cluster as well? I was hoping to just make a temporary check light for as long as it takes to read the error codes!

[Brianmoooore]

It's just an ignition switched live! Pick it up anywhere. I was assuming you were fitting a permanent light to the instrument cluster.
If it's just a temporary hook up you can use battery +.

[Speedtouch]

You can even use a couple of pins in the diagnostics plug under the bonnet; 17 (ECU output) and 12 (Switched +12V) IIRC: http://pinouts.ru/Devices/car_diag_pinout.shtml

(You just need to hook a 12V bulb across them, though I've yet to try it, so don't blame me if it all goes horribly wrong .)

[tomm]

You can even use a couple of pins in the diagnostics plug under the bonnet; 17 (ECU output) and 12 (Switched +12V) IIRC: http://pinouts.ru/Devices/car_diag_pinout.shtml

(You just need to hook a 12V bulb across them, though I've yet to try it, so don't blame me if it all goes horribly wrong .)

This would give the same functionality? It would be a lot easier

[Brianmoooore]

Those aren't E30 diagnostic connector pinouts. Pin 12 is the feed to the ignition light from the alternator, and pin 17 is NC. The green/white fused ignition live is at pin 16 though.

[Speedtouch]

AFAIK, Pin 12 of the under-bonnet diagnostics socket is connected to pin15 of the ECU. Hence, you just need to hook a 12V 5W (max.) bulb across this Pin 12 and the battery +12V to get fault code readings.

(Ignore the bit about Pin 17 above!)

[Speedtouch]

I may well be getting confused here (like i say, I haven't tried this myself yet, so can't validate anything as gospel); I have a diagnistics pinout that says:

Pin 12 = Charge Alternator (D+)
Pin 14 = Battery
Pin 15 = Motronic Control unit (RXD)
Pin 19 = Ground
Pin 20 = Motronic Control unit (TXD)

So, I'd assume you'd need to hook the lamp between either Pins 15 or 20 and the battery +12V...

Sorry for the confusion

[Brianmoooore]

Motronic transmit and receive on 20 and 15 aren't the ECU fault light output.

[tomm]

Anyone know if the current is likely to blow a 12v LED?

[E30Mark]

Anyone know if the current is likely to blow a 12v LED?

Voltage blows things up, not current... The LED will only draw what current it needs to operate, as such you can't push too much current through a device.

Where as voltage will just rush through anything in its way.

[Brianmoooore]

The LED will only draw what current it needs to operate, as such you can't push too much current through a device.

You can if the LED doen't have a series resistor! He says"12 volt LED though, so maybe it has a resistor fitted.

[E30Mark]

The LED will only draw what current it needs to operate, as such you can't push too much current through a device.

You can if the LED doen't have a series resistor! He says"12 volt LED though, so maybe it has a resistor fitted.

I assumed he had a 12V LED, as he said, otherwise it will go pop...

Just to save face from my previous mess i made of Ohms law...

If it's not a 12V LED then you need to run a resistor connected in series to the LED

Resistor value is calulated by dividing the supply voltage by the LED's operating voltage then divide this by the max operating current of the LED, this will give you a value in Ohms of the required resistor.

(Vsupply / Vload) / LED max operating current = xxx Ohms

[tomm]

Update:

This doesn't appear to work, disappointingly.

I took the ECU plug out, took it apart, and found pin 15, which appears to have a plain grey wire coming from it (can anyone point me towards a pin/colour diagram to confirm this?)

I spliced into this wire, and connected an LED between it and the + terminal of the battery.

With the ignition off, or on the first click, the LED was lit; it went out with the key in the second ignition position. It did nothing when I pressed the accelerator 5 times

[Speedtouch]

Perhaps you blew the LED? Try instead with a 12V 5W (max) bulb!!

[Brianmoooore]

I took the ECU plug out, took it apart, and found pin 15, which appears to have a plain grey wire coming from it .can anyone point me towards a pin/colour diagram to confirm this?

Pin 15 is the correct pin. Other end of the grey wire is at pin 12 of the C101 engine loom plug. There will be no corresponding pin in the socket.

[Speedtouch]

This site gives a good pinout diagram of the ECU, complete with Check Engine Light (on Pin 15). Download/open the Zip file for 1989_BMW_E30_Wiring.zip, and see fig02

http://bmwe30cc.org/component/option,co ... lect/id,1/

[tomm]

The LED was (and still is) fine It's a 12v one with an inbuilt resistor.

Having seen the diagram, I'm happy I did it correctly. I guess it just doesn't work for my model of ECU.

[Brianmoooore]

Maybe the low current consumption of the LED is the problem. Try it with a 2.2W lamp.

[tomm]

Why would this be a problem, Brian?

[Brianmoooore]

Because whatever drives the fault light in the ECU may have a minimum threshold current, and may not switch with a LED.