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PTU, Immobiliser or something else?

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Hi all,

A really strange fault with my Zed today (1993 TT Auto), after about a mile, the engine cut out. No misfire, no judder, no warning - it just cut out and all the dash warning lights came on.

I coasted into a parking space, drew to a halt and restarted the car......all good.

Half a mile along the road , the same thing happened, no warning other than all the dash lights on. Restarted again no problem, drove home (another half mile) and parked up.

I checked under the bonnet for loose wires, checked the PTU terminals and wiring  - all okay. Let her idle for ten minutes, again - all okay. No hesitation, she idled away fine.

Took her out again and she cut out again.....pfft.

My first thought was PTU, second was an immobiliser problem ( an ancient Meta system).

Any thoughts guys?



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10 hours ago, ianl said:

Sounds like ptu, when they break they work when cold and cut out completely when they warm up

Yup - my thoughts too. When mine (a series 1 PTU) started to go bad bad, it was a good 30-60 minutes before I could start the car again; then when it gave up completely, I had to wait hours until the engine had fully cooled down.

I have something to say............ It's better to burn out than to fade away..... :tt2:

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Okay, no fault codes found. Forgot to say - I have ECUtalk - doh!

Strange thing, the car sometimes will start now, without pressing the immobiliser button on the fob...

I think (I may well be wrong) that the old Meta immobliser/alarm system is packing up.

Does any one know where on the car, that the immobiliser can be found - or even what am I looking for (square black box maybe)?

Thanks again - Andy



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J: M462 Two button self coding fob for M999T alarm system:

Parts that look like this for the M999T system:

https://www.executiveautocare.co.uk/vehicle-security.htm (scroll down to M999T)

Fitting instructions (pics in the post)




Edited by AndrewG


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  • 2 months later...

I would probably assume that both fuel pump and starter are wired into the two immobilisation circuits. There are two

relays inside the M999T (see first page of instructions) which make and break the circuits. You could pull the two fuses

3A and 20A (see page four of intructions) and see if that disables the alarm and sets the immobiliser relays to closed

allowing the starter motor and fuel pump to operate. Otherwise you can join the two groups of black immobiliser wires

together inside each of the red circles below to remake the two circuits.


Edited by AndrewG


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Thanks again Andrew, I bought and installed(eventually) a plug & play replacement (HPA EVO) alarm/immobiliser.....

No change, the engine stops after about a mile of driving, no warning, no stuttering, just engine stop and all lights on dash.

Shift into Park position (auto) and it starts right away, no hesitation - a mile down the road it does it again.

ECU Talk throws up error 34, knock sensor, that's all. If it was the PTU, surely the EML or a code would flag up?

The car will idle away for as long as you want, no problems - but when you start driving, then the problem arises...

 As it only happens when driving, would a faulty inhibitor switch the problem?

Any help or thoughts are much appreciated.







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