Immobiliser Hell

Hello, new to the forum and new to MG ownership. I bought an 05 MG TF in July. Loved it, until last week.
The central locking has never worked, I noticed that this was because the fuse was missing, tried replacing the fuse, and just got a long blast on the horn, so removed it again and decided that I'd just carry on with no central locking.
All was well until last week. Went to start the car and just got the horn sounding and no attempt to turn over.
New batteries in the fobs, followed instructions for resynching (though I'm not sure how useful that is without the central locking), tried again - same result...just the horn and no starting. Took battery off, was fully charged but charged it some more just in case. More new batteries in the fobs, same problem.
After a while, I disconnected the horn for my own sanity and kept trying. put the 15 amp fuse back in the central locking, still wouldn't even attempt a start.

Eventually found that if i turn the ignition on and then press the keys on the fob a few times, it will start, but this has to be done every time I try to start it.
I am at a complete loss with where to go next, so any advice would be greatly appreciated.

Thanks

Michael

Wake up and smell the catfood. The central locking is not broken because the fuse is out. The fuse is out because the central locking is broken, These cars have common problems in the door lock assemblies. They have a number of sealed microswitches in each lock and they get old and fail. The correct way to go about fixing this is to work out if it is a faulty lock and if so, which one. If it isn't a faulty lock then there is a fair certainty that the body control module (Pektron unit) is faulty. These have a number of unreliable relays and there is a guru who can repair them for a reasonable cost.

This will take a bit of time and some careful and logical deduction. Starting here:

With the horn disconnected, replace the central locking fuse.
Question one: Can you lock both doors with the key at the driver's door?
Question two: Can you unlock or lock all or any doors from the fob?
Question three: If you can lock a door with the fob, does it spring back to the unlocked condition again?

Answers to these will help us narrow down the problem. The good thing is that the fob has been proven to release the immobiliser. I am guessing that you have a round key fob as you have a late car.

The circuit diagrams for your model are in the download section of this site if you are able to use them.

Hi, thanks for the reply. I understood that the fuse wasa out becuase the central locking didn't work, was just happy to continue locing and unlocking manually until such a time that I had the time and resources to investigate properly.

In answer to your questions - no....the fob will not unlock or lock the doors at all, no response. And yes, it is the round key fob.

Very frustrating...mechanical problems I can deal with quite happily...electrical problems are witchcraft.

Thanks again

Michael

Thank you, I will have a look and start trying to fault find

Much appreciated

If you copy this into a well known auction site, it might be helpful.

MG Rover MG/TF/25/45/ZR Professional Relay Repairs to Pektron SCU - 0662P0A

(I'd have a look myself but I have a Certificate of Airworthiness to do on the wife's broomstick...)

I had a similar problem with my 2010 TF. It started with the alarm/horn sounding when I started the car and progressed to the alarm/horn going off all of the time when the engine was running. My wife suggested I put a blue light on the roof and try to style it out!

I contacted a company called Technozen as I thought it may be the SCU relays. They offer a great repair service and advice. after speaking to them I was advised the problem was caused by a faulty battery alarm backup (part number ywk000041). It is a plug in part, and quite easy to replace. The problem has been solved and no more issues since. I would suggest you speak to someone at Technozen (Paul, I think).

Happy to give you any details if needed.

www.technozen-electronics.co.uk

Yes , Paul Brown. He is your man for stuff like this . Great service.

Always looking to learn I've been following this thread and was intrigued by Awindham's mention of an alarm back up battery, new one on me, so I googled the part no. Top of the list was www.waterlessurinals (not taking the p*** surely), then Rimmers show it but only applicable to MG ZR, ZT and ZS as Awindham's car is a 2010 I presume this part is only applicable to SAIC versions yes/no?

Also new ~ about 4 weeks, hopefully this response gets tagged to the topic. So is the item a back up battery for an alarm, or is it a back up alarm siren should the car battery go flat?
Looking at the image that comes up for the part number it looks like a complete siren.
In either case where do I find the item whether that be a back up battery or the alarm siren/horn itself.
any observation gratefully received particularly as I am about to disconnect the main car battery to fix a sagging seat.

The circuit diagrams clearly show that the TF has a battery backed up siren. This will be a unit with a sealed in and soldered in rechargeable battery.

By now, the majority of batteries wil be useless and this may be causing problems. If anybody can spare one I can dismantle, I'll see if a replacement battery can be sourced and use it to do a how to.

As I stumble through an uphill learning experience with a TF this topic is of interest. Has it been possible to find a means to renew the battery in this horn please? Also where do I find this horn and what is involved in removing it.
I ask because we think that the car alarm that woke us up at 4 AM two nights ago might have been our locked up TF in the locked garage. By the time I had got outside to check which car it was the horn had stopped. So all we have to go on was a slightly distant horn sound that was neither strident or with a deep note, but it had some similarities with the sound one hears when initiating the horn test prior to coding in key fobs using pscan.