pauljosef

Experienced readers- I was driving and saw my oil pressure go to maximum and stay there, no matter RPM's. I stopped, turned off ignition and gauge reading went to zero. Turned on ignition key (without starting engine), needle immediately goes to maximum. Off-zero, on-maximum. Took to dealership theorizing it was the sending unit/sensor and they agreed (estimated $400 repair).
After checking it, they call and tell me it is not the sending unit and it must be a wiring problem with my installed radar detector or aftermarket Kenwood satellite radio/navigation system. They rule that out and now tell me that through trial and error, it is a failure in the DME, meaning replacing it with a "borrowed" unit solves the problem. There was no electrical event (like jumpstarting), no change in apparent engine operation/sound/performance,etc. The oil pressure gauge simply went to maximum. I was near the dealership at the time and was watching my oil pressure readings, so I happened to see it otherwise I wouldn't have noticed anything different.
Is anyone familiar with this situation or otherwise have any observations? It is a $2100 part and I am 4 months out of CPO.

IslandS52

since you are so close to CPO expiration I would attempt a goodwill from Porsche. Worth a shot. otherwise if I recall, one of the race teams or shops was sellin a 06 DME in the classifieds not too long ago for under $500. I remember debating purchasing it in my head. you might be able to find something like that or one out of a salvage car.

also, shop the part. my ABS controller on my BMW failed last year and the dealer was $2k for the part, an independent was $1600, but with a little searching I got a new Bosch unit for $540 online. not cheap but significantly less painful.

pauljosef

I chatted with a very convincing Porsche mechanic online who suggests that the dealership's story is BS, largely because they started off telling me that the replacement oil sender would be $100 and 2/12 hours labor compared to his claim that it is $79 part (not a big difference) but 1 hour book and 15-20 minute actual for experienced mechanic. He also states that he has seen MANY oil pressure sending unit failures show up exactly like this ( maxed out pressure) or the reverse (zero pressure). I have good reason to be suspicious if this dealership from past experience. Can anyone confirm or refute these assertions? I am neither a mechanic nor an idiot and very open to advice.

mattyf

I'd get a second opinion, not from the internet, but from another dealer or independent.

pauljosef

I was hoping someone associated with RennList would qualify. I don't see how the dealership's version of events is possible given my understanding of what's DME does and doesn't do. So, has anybody had their oil pressure sending unit go out and had a maximum pressure reading instead of a zero reading?

pauljosef

And what have others paid to have an oil pressure sending unit replaced?

BED997

What is the reading supposed to be at idle, acceleration and cruising at 70 mph once warm? Mine stays high a good bit.

Macster

Some time back I asked about the oil level sending units their robustness how they failed and one senior tech told me had never encountered a bad one while another could only remember one.

He said the in-dash unit provided no reading and after eliminating the in-dash controller he replaced the engine resident sending unit with a new one.

Problem solved.

I note the oil pressure gage of my 996 jumps about sometimes and I suspect this is due to loose connector or a marginal contact which would be made right by disconnecting the sensor/sender from the harness then reconnecting it. Pure laziness on my part has kept me from trying this theory out.

In your car's case this might be the time to get unlazy or have a tech do this for you.

Regarding differences of opinion regarding parts cost and labor time between dealers. Some dealers discount parts (mainly I hear absorbing some of the high shipping costs) and some offer labor discounts for say if the service manager/tech knows the job can be done in less time than book time passing at least some of this savings on to a customer.

Once or twice I myself have benefitted from a nice and unexpected discount in one case transmssion fluid when the dealer received some break on price of what is usually very expensive fluid and graciously passed the savings on to me.

Also, often times a dealer will supply a high estimate adjusting this downward when the actual cost of the repair is known. This is seen in some dealers preferrable to lowballing an estimate only to have to call the owner to get permission to revise the estimate and upward. Ouch.

I note you have some aftermarket electronics installed? I have both a V1 and a NAVI unit installed and a tracking device installed in the OBD2 connector. The V1 and the NAVI unit are powered from the lighter socket in the dash though and are not wired directly to the car's electrical system.

If either of the electronic devices in your car is wired directly the car's wiring system this can be a problem if the installer wasn't too savvy. Often car makers use discretionary pins of mainly the OBD2 connector for their well discretionary needs and along comes a stereo installer who has gotten away with using one of these before in other cars and well trouble ensues.

Now sure, generally in this case that the installer has it wrong is obvious from the git go.

But a sloppy hook up to the right power and ground pins/lines can cause a problem as the connection becomes intermittent which can include contacting one of the other critical communication lines.

In the case of your car I believe the OBD2 bus is ISO-9141-2 or KWP2000. The CAN bus used for the "Komfort bus" which has on it -- at least in my 03 Turbo and my (late) 08 Cayman S -- the dash controller and stereo and such.

So, you must be sure -- if (big if) the add on electronics are wired directly to the car's wiring harness.

If not... nevermnd though you can try to unplug them and see if this makes a difference.

Also check the ignition swich, wiggle the key around to see if this has any effect.

I will note a full scan of the car's various controllers (DME/and others) should flag a bad DME and if this was done and it came back the DME was bad...

But if you can't get goodwill and want a second opinion before springing for such an expensive item, a 2nd opinion is always a good idea.

I have to mention that you need to be careful. If it proves to be the DME while it might have just been time for it to die, it might have been helped by some electrical anomaly possibly arising from the installation/presence of the radar detector/aftermarket Kenwood electronics.

So you want the car's wiring system checked out thoroughly or you could see the new DME go up in smoke after being installed.

Sincerely,

Macster.

TerpsRED

My oil pressure in my 06 C2 reads very high for a very long time, until totally warmed up, then it will come down to around 4ish. I don't really pay that much attention to it now. Sometimes it comes down to the 2.5 mark when sitting idle. I figure I'd rather it show high pressure than none at all.

BED997

Mine does the same Terps. After using the search button otheir articles seem to report the gauge working in a similar way.

pauljosef

The dealership told me there were NO codes reading the DME as bad. They claim to have found it through trial and error. It was this dealership that installed the radar detector and the Kenwood nav/sat was installed more than a year ago by Custom Sounds, a very experianced organization here with a lot of Porsche experiance. I simply don't believe that while I was driving, my pressure gauge maxed out because of something going out in the DME and there was no other symptom. The DME doesn't even send information to oil pressure gauge. I am suspicious that they jolted it while trying to fix the oil pressure sending unit and I am being BS'd.

pauljosef

This is not a weird pattern of oil pressure readings. This is--turn key on (without turning engine on), gauge goes to maximum, turn key off, gauge goes to zero. Over and over again, like it is grounded or something. I was driving when it happened and NOTHING ELSE happened, like you would expect to happen if something went out in the DME. I will bet money that no one who reads this listserve has experienced a DME problem like this.

Macster

Without going into too much detail the failure mode, the behavior, is not that far out.

What can be open for discussion, maybe, is the source/cause of the behavior.

Briefly, the oil pressure sensor input to the DME is a voltage signal that is converted into a digital value by an analog to digital converter peripheral (AD/C) in the DME then this digital data is sent to the instrument cluster where it is converted back into an analog signal by a digital to analog converter (DA/C) peripheral in the instrument cluster controller and this is a signal then sent to the oil pressure gage which causes the needle of the oil pressure gage to reflect the oil pressure.

Any interruption of the voltage signal from the sensor to the DME's AD/C input pin can result in an erratic oil pressure reading. But one hopes this cause has been eliminated.

At the DME the AD/C on the other end of that input pin can fail. There are many of these in the DME and they are rather isolated from each other and the failure of one doesn't necessarily affect the performance of the others nor does it affect the performance/behavior of the DME in areas not directly related to this one input signal.

There is the path and subsequent processing the digital oil pressure data takes and receives from the DME to the instrument cluster controller and from this controller to the oil pressure gage.

This path is probably over a bus that is constantly checked directly or indirectly for proper operation.

The instrument cluster controller does a reverse operation on the digital data using one of its DA/C's conerting the data back into analog which is what makes the gage needle move about.

The instrument cluster controller DA/C peripheral is like the AD/C peripheral in the DME in that it is relatively isolated and generally it either works right or not at all.

Thus the external path from the instrument cluster controller to the gage and even inside the gage itself is suspect.

But the dealer has said "DME".

I guess it boils down to whether you believe/trust the dealer or not.

If you do not then unless someone else comes forth with info that is directly helpful and leads you to a solution that doesn't involve a new DME you are left with the dealer's diagnosis.

You can of course obtain a second opinion.

Now you are being told something rather expensive is wrong and this diagnosis is based on trial/error testing.

Given the amount of money you are looking at spending you are entitled to a bit more detail a bit more explanation as to the how and why this conclusion was reached.

No need to be argumentative or confrontational -- which I'm sure you would not be.

I have found when the few times I've been given a conclusion as to what is wrong, expensively wrong (to the tune of around $3K in one case), when I've asked for some background, some further/deeper explanation as to what led to the conclusion the techs have been quite agreeable to take the time to talk to me, to go over in some detail and to answe my questions.

I didn't expect to receive a full understanding of OBD diagnostics or a full understanding in whatever is involved.

But you have concerns that given the dealer's admission trial and error testing led it to the diagnosis that has you facing a large repair bill you want to be sure the techs are sure that when you have this repair done it is the right thing to do and will address the symptom.

Sincerely,

Macster.

pauljosef

Thank you for taking this time.
I understand you to say that the DME actually DOES monitor oil pressure and that the signal goes to DME and THEN to instrument cluster/oil gauge. I thought that oil pressure sending unit sent signal to oil pressure gauge directly. IF the DME monitors oil pressure, then does it regulate it as well? I thought oil pressure regulation in was a function of a mechanical pump depending on engine RPM's to drive it up or down as a function of RPM's. If the DME monitors oil pressure directly and as an intermediary to the oil pressure gauge, why would it not shut down the engine when the pump failed? If sensor goes directly to oil gauge, then a warning light makes sense, meaning "Hey driver, you have no oil pressure, turn your engine off!" The DME would do just do that and tell you why. And I don't get it why there is no diagnostic code for such a failure since the DME is supposed(?) to the source of those codes. Can you help me understand ? (and if you have the time and inclination, I am not
afraid of details. There is a trust issue with this dealership as you suggest and I am hoping you can explain away my suspicion because I fear they jolted it while diagnosing the problem and don't want to admit it)

San Rensho

Real simple. Replace the oil pressure sending unit and see what happens before you spend $2k+ on a DME.