Hi,

I just purchased a 1991 S4, I’ve owned a 79 and an 83 so I was excited to get this car.

Unlike my first two, I’m getting a few different warning lights (Differential Control and Toothed Belt Needs Service). I have receipts showing the Timing Belt replaced within 20K mi. and the Differential Control seems to be active.

Are these common problems and how would I resolve them?

Thanks for your time,

Darien

 

Take the toothed belt light VERY seriously! It could indicate a lose belt or electrical problem - or a problem that might quickly lead to a catastrophic failure. Unlike your earlier cars, the S4 has an interference engine, and if the belt gives way, your valves will be toast. Search this message board for timing belt failure...

Does the warning come on all the time, or just sometimes, when you drive hard? Either way - do not drive the car until it has been inspected by a competent mechanic with 928-specific experience!!! This might just save you from a 5-digit repair bill.

I know someone who had a constant PSD warning in a '90 GT. He needed a new differential, because no used one was available at the time. Cost was in the neighborhood of $3k.

Where are you located? How many miles on the car? Did you have a pre-purchase inspection done before you bought the car?

 

Have the timing belt (TB) tension and condition checked IMMEDIATELY! No joke ... park it now. If you do not know the specifics, just ask.
Re. the PSD, there are many possibilities, from an ABS sensor, etc. There is a detailed Service Procedure for a fluid change that may well be required and could be responsible for the alarm - search 'PSD'
The Kempf Tension tool is $60 - Nicoles estimate is correct - and somewhat higher for ignoring the tension alarm. It may only be a loose wire - but if it is a loose belt ....

 

Dude........ I just purchased a 1990 model and I have the SAME two indicators on! If you get to the bottom of either problem before me please PM me or put it out on the board! I'll do the same.

 

Darien, welcome and congrats on your purchase. To answer your questions, they are both common problems to the chassis and to resolve them, take your car to a 928 specialist, or buy the work shop manuals and start reading. DO NOT even start the engine until the timing belt tension has been checked, and the whole timing belt path has been checked.

The TB is over 6 feet long and connects the camshafts to the crackshaft in a very detailed orientation. If the belt breaks the valves crash into the pistons thus requiring an engine rebuild. DO NOT start the engine until this is resolved. If you use a mechanic, have the car TOWED to his shop, and get a signed estimate before he touches the car. If you DIY, there are many sites and help available here but you will need the work shop manual (WSM) to proceed. It is very detailed and indespensable for the DIY mechanic.

The other light I'm not sure of because there are two possibles. One is the amber or yellow "PSD" indicator, the other is red "ABS". If the PSD indicator is on all the time, DO NOT drive the car until this has been resolved. This inidicates that the clutches in the differential are engaged all the time, and this will burn them out under normal conditions within a short time. If the ABS lite is on you may be able to drive the car after resolving the TB issue, but you braking effectiveness will be reduced. It is associated with the PSD indicator, and may be a result of a problem in the PSD circuit.

Also please edit your user profile to indicate your car type, year and other details, and your location. When asking a tech question, be as specific as possible, and try to search the archive for relevant discussion. You may answer your own question with a little sleuthing. Try "timing belt" and "PSD" searches. There are hundreds of hits on them.

Good luck, keep in touch

 

Thanks for the very quick responses! To be a little more specific, I’m in Las Vegas and found the car in Burbank, Ca.. The previous owner had the belts replaced along with water pump just over 20K miles now, he said the Timing Belt light appeared approx. 4 mo. after the work (last Jan-Feb). He took it back to the shop and was told the belt was fine it must be an electrical short behind the dash. He chose to treat it like a nuisance and drove it. Since then he has driven it for almost a year now. The light is intermittent no certain times.

As for the Diff Control light, the previous owner stated it has been on approx. the same length of time but constant. His two mechanics gave him the same “electrical short” answer. No problems noted.

I'm very concerned considering everyones replys!

Thanks again,

Darien

 

Well, now I know the car. I saw it early this year when I was in S Cal for business. Just for clarification, an electrical short, is a circuit where the hot or + side of a conductor is shunted to ground. This results in fuse blowing or burning. The TB sensor circuit should be investigated to prove out the wiring defect, or not. Same with the "Diff control light", although I don't know what that is, and have never heard of this specific light on a Porsche.

Either way, you have no idea if the TB or PSD are working correctly or are, in fact, failing. A failure in either end of the car is $$$$$$$$$$$$$$$$$$$$$$. Frankly, if both are failing, it will cost more than the value of the car to have it repaired at a shop. Your call on how to proceed. I bought a car with no TB documentation, and TOWED it to my shop until I could replace the TB. Now I know exactly the condition. If you believe the POs opinion of the situation, I have a bridge for sale on the upper east coast, used, but in god condition.

 

WOW!! Small world How did you come across it? The guy is obviously no mechanic so you can't blame him for believing what he was told. The price just seemed to good to pass, so I'm not sure if I'll come out ahead on this deal now

Thanks, D

 

Famous last words!

Actually it just makes you a bonafide member of the club! Welcome!

 

One of the more knowledgeable 928 owners, Tony Harkins, lives in Los Vegas. If you ask politely, you might be able to get Tony to help you check out the belt situation...

It is "probably" a bad electrical connection, but you really, really need to get it checked by someone knowledgeable on the 928. BTW - that would normally NOT be a "Porsche shop", as that usually translates to a "911 shop", and 911 mechanics often a) don't know anything about 928s, b) don't want to know anything about 928s, and c) will make you pay dearly for having to touch one...

 

I just had the timing belt and water pump done on my 86 at Tony and Son's on Boulder at DI. Richard and Geno there have been working on 928's for years and they have owned a few also.

 

It is interesting how the stories relate: My car came from Manhattan Beach, and the seller also told me the timing belt light was coming on, he had it checked, and the belt was OK. The reputable Santa Monica Mercedes shop that had replaced it, supposedly checked and rechecked the belt tension, and also concluded that the light was bad...

Well, buying my thrid 928, I had already learned a few lessons and took the car for an inspection by a German car nut in Santa Monica. Turns out that belt was waaaaay lose, and the car needed about $3500 in other repairs (leaking torque converter, etc...). Nevertheless, I bought the car, because it was in very good cosmetic condition - something that would be hard and expensive to fix on some other cars I had looked at.

Once the timing belt was retensioned, it started making "grinding" noises, so the mechanic took everything apart and supposedly found that there was some bearing missing in one of the rollers. So, timing belt and water pump were redone, not without further complications caused by the mistakes of the shop that worked on there previously.

The belt was retensioned later and has not given me any trouble since. I have driven about 20k miles with it in the past 4.5 years.

 

Couldn't have said it better. That's award material...

 

Hi Folks,

The deal fell through, I couldn't go through the after affects of buying a car with so many problems.

Thanks for all the help,

Darien
928 owner wanna be!

 

Good for you!