Tiptronic transmission problems

Question

My 1993 model 968 has 57000 miles and has started misbehaving very badly. The Tiptronic transmission will cease to function properly and, worst case, leaves the car inoperable. My Porsche mechanic is good but the tiptronic is foreign to him. Voltage seems to be low when the Tip warning light comes on and things go bad. Checked and replaced the alternator, replaced battery in case of internal short, checked and cleaned all grounds per a tech bulletin he found. Problem is much improved but still happens every few days. Now can be remedied by shutting down and restarting. May require several re-starts to begin actin correctly.

HELP!

Answer

Dear sir,

Intermittant electrical failures are always a problem to correctly diagnose.
I should know, being a qualified auto electrical engineer with 24 years experience and running my own company in Castleford.

You commented that you 'thought' that there was low system voltage when the tiptronic failed.
Did any other systems fail ? What electrical tests were carried out prior to fitting the new Alternator & battery ?

The tiptronic system will probably have a control relay operated when the Ignition is on.
It may be that the relay contacts have carbon deposits across them causing intermmittant
failure. (Recent 911 fuel pump/Ecu fault)

If possible replace the control relay or better still seek a competant auto electrical engineer
who might just be able to pin point your problem.

Regards

Chris Stelling.

 
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