Marti

Hi Guys

I am looking for a little assistance with an electrical issue I have. I have diagnosed a non-start electrical issue on my car (89 S4 non cat) as not having sufficient voltage to terminal 4 of the LH.

I am trying to trace back the wiring for pin4 on the LH as per the WSM advice as I am expecting to find the fault but I am struggling with the wiring diagram.

The EZK relay seems fine (switches on with ignition) and voltage is fine. The LH relay is also fine although I don't believe this is supplies power to pin 4.

Any guidance on where to check for the source of power for Pin4 would be amazing

Thanks

Alan

It is driven directly from the battery - it is one of the additional connections on the positive lug (disconnect, clean, tighten). It goes to the CE panel on CE pin: U12

Alan

Marti

Thanks Alan, if I am reading the wiring diagram correctly then pin4 from LH connects through CE pin W22 which is connected to U12 via a link or wire.
basic question, how do I find U12 or W22?

I will examine the CE but not sure its obvious

Marti

Am making some kind of progress, found the CE connection block W and disconnected that. The volt reading on pin4 LH goes to zero.
I couldn't find continuity between any pin in W block and Pin 4 which is where I suspect the issue is. It could be that the Volta out the CE is 12v but 0.6v is reaching pin4 LH due to a problem.

Is there a way to tell from the CE connection block which one is w22?

We have had very wet weather over the last few weeks and I can see water had gotten in somewhere on the passenger side.

FredR

Marti,

A common problem with these cars is a blocked ac evaporator drain line. This causes condensed water to build up in the drainage trough and eventually overflows into the central electrics area.

Not saying that is your problem given you probably have not used the ac yet this season but should be considered as you chase whatever it is that is plaguing your issue.

Alan

On any of the connectors on the bottom of the CE panel the bottom left pin is 11, the top left is 15, the bottom right is 21, the top right is 25.

U12 & W22 are connected together internal to the CE panel (e.g. on the back). Leave the connectors plugged and test for voltage with a probe in the back of the connector on U12 & W22. Just measure what you have. And do clean the battery connections as noted.

Pin 4 is constant power for the LH retained memory functions, are you sure you are measuring correctly: proper ground, correct range, DC not AC etc.

Alan

Gary Knox

Marti,
Alan Moore has produced a fantastic 'primer' on how to find your way through a Porsche 928 electrical diagram. I recommend you open this link, agree to Alan's terms, then click on the primer, copy it, save it, and print it - then read it several times, and you will find the diagrams much easier to navigate. You, like me, will likely say 'thank you' to Alan every time you open a wiring diagram for diagnostic purposes!!

Link: http://www.moore-fun.net/928-Electri...%20primers.htm

Gary Knox

Marti

Many thanks for the help Alan, it allowed me to work out that my power to the LH was fine and trace the fault to a dead PEM sharktuner chip in the EZK.

Now following up with Jim C about replacing the PEM which is a very unusual failure.

FredR

Never heard of that one before! How did you manage to deduce it was a PEM failure that was the problem [if you do not mind me asking]?

Marti

The laptop was able to communicate with the LH but not the EZK, the sharktuner software acted like no PEM was fitted to the EZK giving a warning message. I swapped the PEM with the OEM chip and it fired right up. It might be the only recorded PEM failure.

FredR

Elementary my dear Watson!

If enough of these PEMs are deployed sooner or later a failure will occur - you were of course just plain unlucky.