autobonrun

A co-worker has a 2002 TT and is getting intermittent oil level measurements. After warming the car up it reads full; a minute later it reads low and the check oil level light comes on. Later it shows full again. The dealer replaced the sending unit and supposedly checked the interconnect wiring. They now say the only other possibility is a bad cluster. They want $4k for a new cluster.

Is there a wiring diagram and description of the signal levels involved in the level measurement circuit? I'd like to see how this circuit works (e.g. capacitance, resistance, millivolt, etc.).

Also, does replacement of the cluster sound right for the next step to take, and does $4k sound reasonable for a price from a dealer? I'm thinking a loose pin out connector at the cluster could cause an intermittent measurement and that should be checked before the cluster is replaced.

rmc1148

I would check for connections also, start with the easiest things first.

"02996ttx50

i'd want to see/inspect the "old" sender unit they "replaced" before anything else got done etc.

not that i'd know what to "look" for!? but i'd put them "on notice", so to speak.

theres also a place in NoHo CA that repairs/replaces clusters for our cars, would be far less that the 4k you've been ( ahem ) quoted.

jpflip

Of course first thing to do is to look for loose connectors....Unfortunately we don't have access to the cluster design in the wiring diagram , just signals from and to.....But you can get the cluster fix! Looked at Qmulus post #12 he seems to be really good at fixing damaged cluster....

http://www.renntech.org/forums/topic...er#entry264064

rmc1148

I need to get over to renntech, good info flip. Hopefully its just a loose connection.

leftlane

I'm with 02 - the symptoms are exactly what happens with a bad sender unit. Ask for the old one and ask them to also check the connections.

Next thing the dealer will say is you must replace the entire car for only $70k.

autobonrun

Good stuff guys. If i'm not mistaken, he was told repair was not an option. It had to be replaced. This is excellent news that I'll pass on.

autobonrun

The sender unit has already been replaced with a new one. Because of the misdiagnosis, the dealer did not charge for it.

"02996ttx50

congrats on the successful repair! that's all that really matters.

it's also astonishing to me how few "options" exist from a dealership, when in "reality"; the options for repair of certain items, are often many, while "approved" is quite another "story" lol

autobonrun

No, the problem is still there. The new sending unit did not fix the problem. The measurement still fails intermittently. The dealer just didn't charge for the new sending unit. Now they're saying he needs a new cluster.

"02996ttx50

ouch. dealerships. i wonder if i'll ever deal them again. probably.

Macster

A bad cluster would not be my diagnosis.

Based on the symptoms my diagnosis would be the oil level sensor is bad.

I've cut one apart. The sensor housing is a long thin plastic tube through which two loops of wire run down then up again. The tube has openings to allow oil inside and to insure the wires are immersed in oil.

One wire is to measure the oil temperature. At the bottom of the loop there is a thermistor which produces a voltage signal that is interpreted as the oil temperature.

The other is used to measure the oil level. This loop of wire starts out and ends insulate but the part that is immersed in the oil is bare. The wire is a pretty exotic alloy too. Nickel/chrome possibly.

The wire forms a long narrow loop that is held taught by a hook at the bottom of the tube.

There are a number of failure modes. If the wire breaks or a connection fails there will be no reading. The techs I asked about the failures of the electronic oil level system told me in the few -- the very few -- cases of a problem it was no reading that was the symptom.

There can be another failure I think. What can happen is the hook at the bottom fails and the wire loop then becomes loose. The amount of the bare wire in the oil then varies from the agitation of the oil in the tank. As a result the oil level reading will vary.

I would be very sure the oil level sensor was ok before even considering a gage cluster replacement.

And before I considered a gage cluster replacement I'd explore having the unit repaired. There are businesses that specialize in gage cluster repair and even if you have to shop the unit there and back the cost is way way less than replacing the unit. A few hundred dollars vs. a few thousand dollars.

Receiver

Looking back fondly at the days of oil dip sticks. Another opportunity taken by Porsche to replace something simple that works by something complicated that costs a fortune to fix when it breaks.

autobonrun

Good stuff. It could be a resistive system but it sounds to me like a capacitative level sensor. The thermistor at the bottom would be used for temperature measurement. The plastic tube we call a dip tube or stilling well; it's used to keep the sloshing liquid from changing the measurement and gives a more consistent signal. The connection at the bottom is to keep the wires from touching the tube. This link below is a boring sounding video but does a good job of explaining capacitance level measurement.


My question is if the sender unit (transmitter) and the sensor are one device or is the sensor separate? When the dealer says he replaced the sending unit, does that mean the sensor was also replaced or could he have kept the same sensor unit? If the latter, I agree that the problem most likely is the sensor rather than the cluster.

Macster

Based on the one I had in my hands the sensor/"sender" unit appeared to be the same thing.

The unit fits into the block from the top of the engine and there is a connector which of course the engine compartment harness plugs into which carries voltage to and from the unit to the DME which converts these analog signals to digital.

However, I have not looked at a Turbo unit. Perhaps (perhaps) the unit is different?

For the real answer to your question you probably need to speak to the senior tech who should take the time to describe the system. I'd have to be darn sure there was nothing overlooked to address this problem before I sprung for a new instrument cluster.

Before I did this I would research having the unit sent to a facility to be repaired.

And did. When my Boxster's airbag warning light came on and there were no error codes associated with this, when a new controller failed to extinguish the light, when a borrowed instrument cluster didn't manifest the lit air bag light I got in touch with a guy at the Lake Havasu AZ VDO Repair facility.

The link is IIRC:

www.vdorepair.com


There is Palo Alto Speedometer (in Palo Alto, CA) which has received good word of mouth, too.

Here's a Palo Alto Speedometer link:

http://www.paspeedo.com

There are I'm sure equally quality facilities scattered around the country but those are the two I have heard about.

The local dealer sent my instrument cluster to the VDO repair facility and some components were replaced, but unit came back with the light still on. Either VDO did not charge for this or the dealer ate the cost.

After I got the car back, I called and spoke to the VDO repair tech at the AZ facility and he told me I could send it back and he could either move the unique data from my old cluster to the new (used/rebuilt/refurbished) one or perhaps try replacing something else. I don't recall the details. I had more pressing things to deal with and I just had the tech install the unit back in the car for now.

Then I -- and I'm ashamed to admit this -- but for now for a temporary, ummm, fix I just applied a bit smaller than a dime sized piece of electrician's tape over the warning light. Sigh.