Thatcham alarm and immobilizer

Tiny
TWIZTWIZ
  • MEMBER
  • 1994 VAUXHALL FRONTERRA
  • 2.0L
  • 71,000 MILES
Car immobilizer fails every third time of use when unlocking drivers door. It's not a remote key. Sometimes when unlocking and re-locking it works again and then fails on third attempt next day after locking car door. I have to keep disconnecting negative cable and leaving for 1 minute to disconnecting both leads. Sometimes it's works again until third attempt or overnight with car securely locked it cranks over but is locked down as injection so it starves it of petrol. It doesn't like one key especially and if used to lock door it locks me down for days again despite repeating all the above processes. Life's a nightmare as disabled and rely on car for shopping. Have checked battery and even charged it. Somebody disconnected sound of alarm but cannot remember what they did. Were under bonnet or wheel arch passenger side. I will try and get pack of fuses but don't know what size they are in case it's something there. It's a right hand drive. Any help please would be appreciated. Thanks
Friday, April 24th, 2020 AT 3:19 AM

4 Replies

Tiny
STEVE W.
  • MECHANIC
  • 14,572 POSTS
Your description sounds like the switch inside the lock assembly that tells the alarm system that the car is unlocked is worn out and not working. The part that says one key works better also suggests this as the worn key may not be moving the cylinder as far as the better key. The switch is in the latch mechanism so requires the latch be replaced to repair it.
Image (Click to make bigger)
Thumb
Was this
answer
helpful?
Yes
No
Friday, April 24th, 2020 AT 9:33 AM
Tiny
TWIZTWIZ
  • MEMBER
  • 3 POSTS
Thanks for taking the time to respond. Much appreciated. I had door switch replaced a couple of years ago as drivers door wouldn't open at all. Fuse from central locking was removed back then and I haven't replaced it. Doors all unlock and open okay without central locking fuse. The Thatcham alarm and immobilizer ECU memory part has to be cleared by disconnecting both battery leads but maybe I should totally clear memory by leaving lights on as well as heard Thatchams hold a little charge still and last sequences in it's memory, whether it was the good part that started the car, or the bad part that immobilized the engine. If I get engine started it likes me to drive over 30 miles and everything resets itself. I recently drove over 30 miles but stopped at shop and left good working key in ignition with engine running in case it didn't start again and used the key it doesn't like to lock the door whilst engine was still running. If I use this second key it doesn't like it and causes these immobilizer issues, running in This usually limp mode until I drive over 30 miles again. The alarm siren fuse or cable and flashing lights fuse was removed by somebody when battery went flat over winter when I didn't drive it for months following a back operation and alarm kept going off intermittently at night. A new battery was put on and this is when alarm immobilizer problems started. Unfortunately they cannot remember what they removed and from where. If I could work this out and get alarm siren and flashing lights working, maybe immobilizer would reset itself and work again as long as I do not use the spare key in any of the doors which messes it up again with only that key.
Was this
answer
helpful?
Yes
No
Saturday, May 2nd, 2020 AT 9:53 AM
Tiny
TWIZTWIZ
  • MEMBER
  • 3 POSTS
Also noticed the other day 4 lights come up on dash. When one went out I tried again and it started but didn't when I tried it again next day.
Was this
answer
helpful?
Yes
No
Saturday, May 2nd, 2020 AT 10:00 AM
Tiny
STEVE W.
  • MECHANIC
  • 14,572 POSTS
I would get a new key made and see what it does. It sounds like it has a couple issues, the fun one would be determining what they did. You could use a scan tool to see what is going on.
Was this
answer
helpful?
Yes
No
Saturday, May 2nd, 2020 AT 10:52 AM

Please login or register to post a reply.

Related Disarm Content

Security System Reset
GUIDE
Security System Reset
Need to re­set the se­cu­rity light in your car? If the se­cu­rity light is blink­ing the im­mo­bi­lizer sys­tem is en­abled and will not al­low the car to start.