Full battery but no crank

[Niklas 71]

Car: Cayenne turbo 2004, 250 000 km

The problems have been cascading over the summer, starting with a trashed rubber bushing on the cardan shaft support bearing. Before I got home and could fix that (thanks to a great description found in this forum!), the PSM and ABS lights went on. I guessed it was caused by the occasional knocking and wobbling of the cardan shaft.

After fixing the support bearing, the lights stayed on, so I bought an iCarSoft POR II to read fault codes. For some reason, it couldn’t pull codes from the PSM, but there was a fault code in the gearbox controller, about a lack of speed signal from the rear left hand wheel. 
I gladly bought a new ABS sensor and replaced it, with no luck. I could remove that fault code but the lights returned and I still couldn’t pull codes from the PSM.

Next, I lifted the floor mats and found a lot of water on the passenger side from a blocked sunroof drain. Much of the wiring was corroded, so I carefully replaced it wire by wire. At the same time, I put in a new battery since the old one was really weak. The car started and ran fine, but the PSM and ABS lights kept coming back.

 

Next, I wanted to inspect the PSM, so I lifted the plastic cover beneath the wind shield and disconnected the DME in order to get down to the PSM.

The PSM connector looked fine without any traces of corrosion. The same was true for both DME connectors. I just brushed off some dust and put everything back together.
 

Here’s where my biggest problem occurred: now my car won’t crank the engine at all. When I turn the key, the instrument screen says that “daylight running lights are not active” or something similar. The cooling fans revv up to max but nothing more happens.

 

i have tried disconnecting the battery for an hour and then reconnecting again without any different behavior. 
 

Any ideas on how I can bring my car back to life again?
 

Regards,

Niklas in Sweden

[Niklas 71]

Oh, and I have also tried pulling out the DME again and resoldering all the cable joints close to the smaller DME connector, but that didn’t help either.

[Niklas 71]

After continued troubleshooting I have learned a couple of things:

• All ground connections for the DME is OK
• The K-line connection to the ODB2 connector is OK
• CAN-drive connections are OK
• Pin 62 (Terminal 30) has a permanent +12V as it should

But: Pin 3, designated "Terminal 15 via relay" only has a 6V level, even though it is described as "Main power supply via DME relay". This sounds like a possible cause for my problems, as I would expect 12V here.

 

Does anyone know where I can back-track pin 3 to this "Terminal 15 relay" where it is feeded from? I have so far been unable to find any diagrams that show this. 

All help would be appreciated!

[brendan caunt]

• I also have the same problem but 0volts to main power of dme 

[Rick150]

Don't know if this is much help, starter circuit.

 

 

[Niklas 71]

Do you mean 0V on the main power supply lead? That one is fed through a relay controlled by the DME.

 

I bought a used kit with DME, KESSY, ignition lock and key via Ebay. Tried all parts tonight, but the display said ”Immobilizer active” or something similar. I switched back to original lock and key with the same result. Then I switched back to my original KESSY as well, but with the new DME still in place. The symptoms then went back to what they were with my original DME. 
 

I hope to get more tests done this  weekend, will report back with my findings.

[Niklas 71]

I finally solved my starting problem!

When I was fiddling around with my iCarsoft POR II, I noticed that the brake light signal to KESSY was missing, despite my brake lights being active when I pressed the pedal.

The brake light switch has two different 12V inputs, where one was missing from fuse #26. I followed the lead towards the left fuse box and found a dodgy looking cable Splice. Soldered that, and got my car running again for the first time since September!

Now there’s only an intermittent PSM fault left to solve, but that’s a different story.

//Niklas