Mi16 Diagnostic Light Function

[sport1901966 8]

Hi all,

 

I have read through a couple of topics on the use of the 2 row Mi16 diagnostic light/switch wiring and interrogation but I'm still a little unclear.

 

I am designing a new loom and am more or less finished but I want to change the diagnostic wiring so the diagnostic process is easily performed in the car without attaching any other equipment. I know how the diag process is performed but just want to clarify the original loom wiring if someone would be so kind. I have sketched this diagram below, am I correct in believing this is the original wiring - where by the components in red are added when the diagnostic procedure is to be performed?

 

 

Also what is the point in the wire from ECU pin 12, nothing I have come across uses it at all?

 

Thanks,

Geoff

[welshpug 1,657]

I dont know specifically what the function of wire 12 is, likely to be for some old dealer diagnostic stuff, have a Bosch book at home though so if I remember I'll have a read through see if I can find anything on it.

 

Cars from around August 89 have the wire for the k-light in the dash loom, I think its 74a (red wire) so you may be able to wire the light in permanently

[sport1901966 8]

Cool that will save putting in my own MIL. Is my understanding of the original circuit and layout (i.e. position/grouping of diagnostic wires by the Fuel Pump/Injector Relays) correct then?

 

On that basis if I were to wire as per the diagram below would the diagnostics function correctly

 

 

Thanks for the help

 

Geoff

Edited October 11, 2011 by sport1901966

[JoshGti 8]

Essentially yes, although you dont have to worry about wiring the diagnostic light to the ignition switch. Instead of following wire 74a yourself (i did it earlier today) it goes from the back of the clocks all the way to the fusebox side of the car and back towards the two brown multiplugs under the drivers footwell. If you look at one of them, pin 4 on the plug has a red wire one side but no wire connected the female side of the plug.

 

Wire the diagnostic wire straight to this and put a bulb in the back of the dash and it will work straight off the bat.

 

The other wire with the earth button is correct to my understanding.

[sport1901966 8]

Thanks Josh thats great. I put the ignition switch section in just for the sake of showing a simplified version of the circuit to check my understanding. I had assumed the other side of the bulb receives 12v when the ignition is on in some way or another, and hence the ECU earths the bulb when displaying the codes as opposed to supplying 12v.

 

Cheers for the help guys my loom plan has been modified accordingly!

Edited October 12, 2011 by sport1901966