understanding 1999 immobiliser

[Steptoe's photos]

Does anyone understand how the immobilisers of this era function ? Four wires out of immobiliser connect to three pins of the ECU.

Two black/red trace join close to immobiliser and arrive as one at the ECU

But what is it travelling along these wires, and in what direction?

There is no ground or earth wire in the diagram so I reckon grounding is via the ECU as with most of it's controls being earth switched.

I have been back probing the plug at the connected immobiliser an think I got nothing from these wires while DMM was connected to ground. Things may change if I use the diagnostic grounds found taped up with the diagnostic test plugs or most likely if I probe with ground/black DMM probe and the red probe connected to battery positive

Surely these wires do not carry Ohms or rolling codes ?

All in prep to understand the immobiliser for a donor job

[lmdew]

What does Subaru immobilizer do?

 

An engine immobiliser is an electronic device which is fitted to the engine, preventing it from starting without using the correct key. When the key is inserted into the cylinder, a vehicle ID code is transmitted to the body integrated unit, which compares it to the code it has been registered with.

 

Bunch of links on a Google search.  Too new for me!

[nvu]

I haven't worked on it myself.  From what I understand with the USDM immobilizers starting on 05 on, they are matched to the ecu that came with the car.  People doing engine swaps have the old key taped to the immobilizer antenna and tucked away.  We didn't get immobilizer models in US until 2005 so I'm guessing your 99 would be the older style.  It's not simple voltage/resistor to bypass.

https://iwireusa.com/blogs/iwire-university/what-does-it-mean-that-my-subaru-is-immobilized

[Steptoe's photos]

nvu - Your last sentence is what I am afraid of. I think the 1997 model here may have been immobiliser free. I have 1998 manuals, and applying to what I find in my 98 built 1999 model year beast. Also looking at a 2000 built 2001 MY donor.. For anyone reading, the immobiliser "antennae" is the plastic ring around the ignition barrel, two wires between it and immobiliser module.I might need to hit Google USA for more links Imdew

[Steptoe's photos]

these immobilisers know when a door is open (manual suggests driver's door) a tiny Voltage about 1.0 V shows up at the plug when door is open, then 12V when door is shut !

Then, the little switch right at the mouth of the ignition barrel knows when anything has started to be inserted. A wire comes from fuse panel to power this one, outgoing telltale wire then to module. Two more wires around ign barrel are for the antennae ring around outside of barrel - known as a key reader in some beliefs.

[el_freddo]

Dunno if it’s the same as a an ‘02 GT foz loom that I cut down, I’m yet to test the immobiliser gear in that mix but I have all the bits I need intact for it to work. 

While I was doing that work I drew out the immobiliser wiring pin out on one document. This has since proven to be correct across a number of Subaru model years with slight variants in their wire colours. I can email you this document if you wanted to check it out. 

Cheers 

Bennie

[Steptoe's photos]

19 hours ago, el_freddo said:

Dunno if it’s the same as a an ‘02 GT foz loom that I cut down, I’m yet to test the immobiliser gear in that mix but I have all the bits I need intact for it to work. 

While I was doing that work I drew out the immobiliser wiring pin out on one document. This has since proven to be correct across a number of Subaru model years with slight variants in their wire colours. I can email you this document if you wanted to check it out. 

Cheers 

Bennie

Thanks Bennie. I have 1998 MY wiring diags, and these tie in with 1999MY on most things. When I can get this Bermuda special running again, and sort it's massive whumping, intermittent engine/fuel/ignition cut, I will be back into this ....I think