Hi, my 2006 Forester is totally immobilsed.

Been off road for a couple of months, and was turning it over until the very cold snap a few weeks ago, battery died. It needs to go for MOT but will move on to my property and SORN (not an issue).

Car is immobilised but I can gain entry by key. Central locking does not work remotely by fob.

Ive put a brand new car battery in. The car was completely without power for a few weeks. New batteries in both original fobs. Windows and lights work.

On insertion of key in ignition, indicators flash rapidly and alarm will trigger after 30 seconds, can only turn off alarm by turning off ignition.

I have original silver key code stickers. The code might have been changed by previous owner - I had no need to use before battery change.

I believe the alarm is a Thatcham sigma system with the multifunction keypad and i have original Subaru paperwork including ECU serial no.

Its a second vehicle bought because of memories of another Forester years before and has generally been reliable, and body is in great condition as is interior but probably not worth a lot, and nothing in current state so I just need to understand costs to balance whether it is economically viable to fix this issue before I start other work - and how to/what do I do next?

Local-ish auto locksmith doesnt want to touch Subaru and another wont give any estimate before arrival. Im in a town with no nearby Subaru specialist.

Can you advise how to reset keyfobs/code to immobiliser and alarm / solve the problem?

Thanks in advance.

If it were me I would try every sequence in turn and ensure that I am sat in the drivers seat with all doors and boot/bonnet closed.
Sometimes its a case of trying different variables and seeing if the outcome changes
Please let us know how you get on with it all

I will keep trying. Interesting comment as i have had bonnet open. Thank you-I will close and retry.

to be honest I do not know what im doing. I recall my first forester and having to put a pin into keypad but that was with the seller. So long ago Ive forgotten sequences and do Inuse star button or hash before/after?

Is there a handy guide on the internet somewhere to getting keyfobs and alrms going ?

Ive tried searching through the subaru youtube videos. Most not for 2006 era vehicles, or for UK variants.

Reality is it not that big an issue overcome one way or the other .
Options are disabling the sigma m30 and bypassing immobiliser circuits (rejoining wires the 2 immobiliser circuits spliced into) .
Trying to get the current Sigma working to some functional extent again or replacing the modules with known working used ones (needs be supplied with pin code and/or working fob allow easy programming).

No need be a specialist in Subaru as this System is basically added after production line assembly and Sigma systems used on many vehicles in that era including a lot of euro cars .
Basically any fairly competent auto electrician, alarm installer or decent mechanic can do this work as it nothing fancy and all you really need is a brain and a multimeter, wiring info is helpful but not a must .

What I would do is do few basic things see if can get alarm to function, main thing that goes bad is the siren that located under the wiper plastic trim and sits in the cowl space, this has a P9 rechargable battery inside and they go bad and leak and decay the siren board causing various alarm function issues, just unplug the wire that goes to this siren and test alarm, Also test alarm by having ignition key on and pressing fob button and see if that turns immobilser off ! if does alarm may start function normally again if lucky .
You can leave siren unplugged and only issue is you get no siren tones but all will function if rest of system good .

If system seems totally unresponsive simplest option is bypassing the Sigma alarm and that pretty quick job to do, only downside is loose the remote central locking as sigma alarm install removed the factory subaru remote locking .

The Sigma alarms are nothing but potential problems at 20 years old as it euro made crap, all the Subaru Japan electrics and electronics will be fine and they all independant of the Sigma (besides remote locking) .

Even with the Sigma bypassed you still got the Subaru factory transponder key chip immobiliser and that good enough on an old basic Forester . Modern car thieves be lost at trying deal with a car with a physical key and a mechanical handbrake lol .

M30 document attached which might be helpful and does include info on pin code use. changing pin code and programming remotes .

m30.pdf

2 hours ago, Mr B said:

Reality is it not that big an issue overcome one way or the other .
Options are disabling the sigma m30 and bypassing immobiliser circuits (rejoining wires the 2 immobiliser circuits spliced into) .
Trying to get the current Sigma working to some functional extent again or replacing the modules with known working used ones (needs be supplied with pin code and/or working fob allow easy programming).

No need be a specialist in Subaru as this System is basically added after production line assembly and Sigma systems used on many vehicles in that era including a lot of euro cars .
Basically any fairly competent auto electrician, alarm installer or decent mechanic can do this work as it nothing fancy and all you really need is a brain and a multimeter, wiring info is helpful but not a must .

What I would do is do few basic things see if can get alarm to function, main thing that goes bad is the siren that located under the wiper plastic trim and sits in the cowl space, this has a P9 rechargable battery inside and they go bad and leak and decay the siren board causing various alarm function issues, just unplug the wire that goes to this siren and test alarm, Also test alarm by having ignition key on and pressing fob button and see if that turns immobilser off ! if does alarm may start function normally again if lucky .
You can leave siren unplugged and only issue is you get no siren tones but all will function if rest of system good .

If system seems totally unresponsive simplest option is bypassing the Sigma alarm and that pretty quick job to do, only downside is loose the remote central locking as sigma alarm install removed the factory subaru remote locking .

The Sigma alarms are nothing but potential problems at 20 years old as it euro made crap, all the Subaru Japan electrics and electronics will be fine and they all independant of the Sigma (besides remote locking) .

Even with the Sigma bypassed you still got the Subaru factory transponder key chip immobiliser and that good enough on an old basic Forester . Modern car thieves be lost at trying deal with a car with a physical key and a mechanical handbrake lol .

M30 document attached which might be helpful and does include info on pin code use. changing pin code and programming remotes .

m30.pdf

Mr B, many thanks for response.

An auto electrician (via email) has advised removing unit and a helpful call from Subaru Replacement Key Services seems to confirm alarm unit ECU is dead ?? >>

>>No LED in dash, no light flashes on keypad when inputting digits before key inserted. When key inserted the keypad light flashes several times on each digit entry.

Alarm DEFINITELY working. its loud and annoys neighbours and puts me off trying to do anything.

If I can get a replacement unit is it an easy swap out ? I dont possess a multimeter but inexpensive. Im not overly technical, or experienced. If replacement failed, Id go to a bypass route and sacrifice remote central locking.

Currently only the drivers door is locked by key…

As immobiliser system appears completely unresponsive but alarm sounds what would you recommend next?

Thanks

As mentioned before you can buy a used alarm main unit and plug it in and program your fobs to it and set a new pin code for it if so wished.
Only plus with that is remote locking be functional again .
Downside is you still dealing with 20 year old european electronics and as it basically can leave you stranded it best pulled out and binned as saves same issue twice (siren board corroded/faulty by leaking P9 battery being super common).
I done repairs both ways for customers (option tended to be driven by their preference on alarm and locking). you can add a remote locking system if pull alarm but that adds cost .
A working M30 used module is cheapest fix with everything same as owners already use to .
You can find used M30 modules pulled from Subarus for around 80 to 150 quid, it must come with pin or a working keypad ( I like a keypad with it as then you got a third keypad that can be used for parts in your key should one of yours fail and it generally easier programming using an existing remote than using pin code) .

You got options and none are technically difficult or needs specialist equipment thus the cost to resolve it either way is not crazy money .
If you half competent and can google info you could swap alarm module or even bypass it to get running as it really nothing more than cutting and joining some wires ...

Thanks Mr B.

Ill try to replace the unit. after that I will bypass…

If you have any reliable resources on bypassing this unit Id be grateful to receive.

i much appreciate you taking the time to respond to thread

I have a 2005 Forester and have the same problem since replacing the battery in the key.,the key worked remotely, has one button only press once to open car and one more to lock the car, there is no led to light up and show that it is working. It does not come with a separate key fob. The 2005 car manual does not show this key. None of the info that I can find on line covers this key either. Has anyone on this forum got experience of this type of because I am totally beaten by it. And it doesn't come with this key pad that the manual talks about but does not illustrate. Any advice would be much appreciated as I am completely flummoxed.

I would replace the battery with a proper branded make like a Duracell button battery.
I have previously experience similar issues with cheap batteries.

Best best is to reverse everything you have done until you get to a point where you will fall across the fault

This is the key that came with our 2005 Forester. I cannot find any reference to this key in Subaru manuals or online. Does anyone recognise this key, have this key with their Subaru and know how to reprogram it. I am at a loss, surely someone has the same key? Any help will be much appreciated

We do have one working key and I think we the pin number for this key also.

I would be careful not erase the only other working key.
Your best bet would be to go to a locksmiths that deals with automotive keys and they should be able to reset it for you when they install a quality battery

On 3/17/2026 at 4:40 PM, Fratton Fred said:

We do have one working key and I think we the pin number for this key also.

The pictured key is totally normal key see with a Forester SG SG9 with the Sigma M30 alarm .
It basically the normal Subaru Key that has a custom housing done by Sigma to house their alarm fob board .
You either fitted battery incorrectly damaging battery contact terminals or the board gone bad in process of swapping battery (or already bad prior to battery swap ! ) .
You certainly want to recheck the battery fitment but I assume you put battery in it as remote stopped working so is the potential fob fault rather than battery at fault (common for buttons go bad on these) .
The instructions for programming remotes is in attached document in this thread .
Another good option could be sending your keyfob off to a remote key repair service, this is somewhere in region of 25 to 40 quid .
A lot of auto locksmiths won't touch these as that old they got no Sigma interface cable or software or experience on them .
Other thing you can do is buy a ussed key same design (easy get off eBay as it nothing uncommon) and put the fob board from that in you Key and program it to your car Sigma alarm .

Mr B. Thanks for your help with this issue, the attachment provided, refers to a key pad to input numbers and codes , what is this, we do not have one?

You do, it is mounted in dash pull out coin tray near the drivers door (in vicinity of your knee when sat in drivers seat ).

You should have a 4 digit pin code that can be used with this keypad to arm/disarm alarm and do some setting and programming tasks..

If you have at least one working remote you can do programming using that remote (you can also use a working remote to program a 4 digit code should you not have one or code you have appears not to work, sometimes original code gets changed by a owner and documented details not updated . )

Before programming remotes I would highly advise you see if any 4 digit pin code you have works with alarm and learn how operate keypad with this code and get some feel for things prior to trying anything such as programming remotes or setting a new pin code .

Once you know you have a working pin you could try reprogramming remote but you want be 100% sure battery fitted correct and good before doing that .
If you read the attached document fully you will see instructions on using remote for programming rather than pin code and this is procedure that I find easier and more consistent in use .
The keypad and beeps/flashes can be a bit funky to get use to for programming so don't expect perfect result first time and be sure educate yourself well before using it and be prepared for some learning to take place during trying to do the process .

If the current not working keyfob doesn't seem respond during programming the most likely conclusion will be it faulty then you either want send it out to a repair service or buy a used known good one off eBay and program that one then swap the fob board into your key ...

Used keyfobs and keyfob repair services can be found on eBay .