Brett968

What you are showing in your picture matches up with this one as far as I can tell: https://www.pelicanparts.com/techarticles/Porsche-Cayenne/40-ENGINE-Valve_Cover_Gasket_Replacement.doc/images_large/pic18.JPG

Gotcha. I see now that the Gogal-branded CCV is not available from Amazon anymore. Bummer! For people that may read this thread in the future, Polar Bear, Inc. should have the correct valve available--albeit for a few dollars more than the Gogal. The trick is getting the right one. It looks a lot like their EX 007 but you will need to verify! Currently selling for $62.79 with free shipping.

Did you try replacing the CCV first (which, of course, is a part of the compressor)? Just curious...

As far as I know, there are two aftermarket solutions for the diaphragm valve from separate manufacturers: a less expensive diaphragm-only solution from a Russian outfit, and a more complete solution that includes not only the diaphragm but the spring, cap, and internal plastic support. In my experience, the Russian-sourced diaphragm does not work properly as the geometry is not quite correct. I have not tried the other option yet--but it looks to be better from the images I've seen. (I repaired my original diaphragm with adhesive and it's holding for the time being.) You can find either of the above options on eBay from various sellers. The second solution is also available on Amazon: http://a.co/3fXpUra

A few relatively easy things that I didn't see on your list: Have you replaced the valve cover gaskets? At this age they are almost certainly rock hard. Check for seeps around the gaskets. These can leak and cause stumble at idle and low loads. Another thing to check is the diaphragm valve for the crankcase vent. These diaphragms are notorious for tearing. It's located underneath a round black plastic cap on the driver's side of the engine towards the front of the vehicle, and is held on by a few tabs. You can inspect the diaphragm by removing this cap--carefully pry it off with a few screwdrivers. Look carefully, sometime the tears can be hard to see. The diaphragm is not available as a separate part from the dealer but there are aftermarket replacements. Keep in mind that some O2 sensor fault codes can be caused by leaks in the intake system.

I also tried the deep vac and recharge with new drier. Then I repeated the same steps with a new expansion valve. No dice. My car never blew cold, even on long road trips. Other than that my symptoms mimicked yours fairly closely. Your high side pressures seem low, and your low side pressures seem high. After I repaired the CCV, as I recall my low side pressures were around 20-25 psi tops. Low side pressures with variable displacement compressors tend to be lower than those of older clutched compressors--so you can disregard all those online pressure charts (which are targeted to old clutched compressors). My high and low side pressures before I repaired the CCV were similar to what you are seeing.

OP, you might want to check out some of my posts on a similar issue I had with my car. Your symptoms match mine quite well. The problem was the compressor control valve (CCV):

I agree with the others. It sounds like they are parts slinging at your expense instead of performing a proper diagnosis. The Motronics version used in these cars has sophisticated algorithms for detecting faults in components such as the MAF and provides "limp-home" modes that should keep the engine running, albeit not optimally. So to answer your question, a bad MAF would not normally exhibit the symptoms you described at all. It is highly unlikely that a bad MAF would kill a DME or that a bad DME would kill a MAF. You should be able to pull the electrical connectors to both MAFs and the engine should start and run.

Yikes, bet that is pricey! Why not buy a used DME off of eBay?

Are you able to communicate with the "Gateway" controller using Durametrics? It isn't clear to me if your vehicle has the gateway built into the instrument cluster or if it is a separate unit. If you can't communicate with the gateway then I suppose it is safe to assume that the gateway is internal to the instrument cluster on your car. In that case, then what you posted is all the diagnostic info available. I have no idea what the Kenwood CAN interface might look like. Can you find some part number on it that you could google? I'll briefly try to explain the topology of the CAN system on the Cayenne. There are three separate CAN networks: Drive, Comfort, and Infotainment. Each network uses a twisted pair of wires to allow communication between all computers on that respective network. Any fault in the wiring can bring down the whole network (limited communication is available in a single-wire "emergency" mode). This should make it obvious why powertrain controllers are on a different network then things like power seats, etc. The networks can exchange messages between other networks through the gateway. 469 is telling as it suggests that you have a wiring problem on the CAN Infotainment network. The Infotainment network includes PCM 2.1, wipers (?), and compass. This explains your wipers and radio controls not working. It also explains error code 459. I don't understand how it could trigger the first three fault codes as these are related to the Comfort CAN network but then again it's not unusual for faults to trigger "limp" algorithms with rather unexpected behavior. Anyways, I thought pulling the aftermarket radio CAN interface was an obvious first thing to check as it's one of the few modules using the Infotainment CAN network and you are clearly indicating a wiring fault on this network.

Even if it is hooked up correctly the radio may have developed a fault that is taking out the CAN line. Is your aftermarket radio interfaced with the steering wheel controls? I would do this. First, check the "Gateway" computer for fault codes. Then -- depending on the fault codes -- pull the stereo and disconnect the CAN lines. You don't have to know which exact wires are the CAN lines, just pull all the connections to the stereo. If your radio uses a separate CAN adapter then be sure to disconnect the factory wiring from that also. After doing this, see if the problem is still present.

Sounds like a CAN communications problem. Check the fault codes stored in the "Gateway" computer. Do you an aftermarket radio by chance? If it is wired incorrectly it could kill the CAN line. Correcting the wiring will rectify the problem in that case.

I feel the same way about my cars. Hopefully it's just a wiring issue somewhere. BTW, the ground for the control side of the relay is the ground for the DME (pins 1&2). The other relevant ground point is the ground for the fuel pumps themselves. The manual isn't very good at spelling out exactly where this is. According to the wiring diagram, the point is MB33 and it is located at the "top left of "C" pillar". However, in the "grounds location" section of the manual it says MB33 is "near center of vehicle". I think RFM's post describes where the actual location is.

No doubt that failure of an unmolested DME is a rare event. It can and does happen though. Has the DME ever been opened for any reason (e.g. chip tuning)? If it came down to it, there is an inexpensive way to replace the DME; just buy a used DME off ebay and copy the immobilizer data from your original DME to the replacement. The only issue is finding someone with the equipment to copy the immobilizer data off of the diagnostic EEPROM. As for the wiring diagram, I don't believe I am allowed to post that here as it is copyrighted material. If you look around you can probably find the full factory manuals for a very reasonable price. @Lewis- Yeah, LOL, I thought the 2 dry solder joints story sounded fishy.

OK, so let's explore the possibility that the fuel relay fault code was not due to you pulling the fuse but that it is indicating some actual fault. I'm assuming that when you say it is still throwing the fuel relay code that this is after erasing the fault codes (i.e. the fault code is returning on the next start attempt after be cleared.) Things to check: Connectivity check between pin 37 (GRN/BLU wire) on DME connector and terminal 85 on the right fuel pump relay The same between pin 65 (GRN/RED wire) on DME connector and terminal 85 of left fuel pump relay If this checks out then check connectivity between each of these wires and ground (separately of course) with ignition OFF. Should be infinite. Check connectivity between each of these wires and ground after engine is started (you'll have to splice in). In the brief 10 seconds that the engine runs the resistance should be low (less than 5 ohms probably), indicating that the fuel pump relay is being activated. Alternatively you can measure voltage across these wires and +12 during the same conditions. If all of this checks out then I would look at the DME. It could be that the fuel pump lines are being driven low correctly (this would activate the fuel pumps) but there is a problem inside the DME with the load detection circuitry on one of the two pins. (The DME switches each of these fuel relay pins from a high impedance state to low (ground) and then a separate part of the circuit measures the current running through each pin to determine if the circuit is behaving as expected. This is reported back to the DME microcontroller. All of this is integral to the DME.) If it gets to this point I can give you some pointers but you will probably need someone comfortable with electronics to perform the checks. (Disclosure: In my former life as an engineer I worked extensively with Bosch Motronics electronic hardware as well as software calibration / algorithms.)