Two-year rebuild, now immobiliser issues?

Hi Folks, I'm hoping someone might have some thoughts on this strange situation. I recently completed an engine rebuild on my 2003 C2 3.6 whose LN ceramic bearing failed after only 65,000km. The rebuild took two years end to end as I had to shelve it for periods due to life's other challenges. It fired up almost a month ago and all was well with about half an hour of test drives around my "private test track" and 10km run into town for the equivalent of your MOT. So far it had behaved perfectly. But during the short test drive for registration (MOT equiv.), it stalled on the inspector and would not restart. Of course I nearly died fearing an engine problem but no all was well, we had all lights and electrics working but no crank. After maybe 15 mins checking fuses etc it cranked and started perfectly, but then stalled at idle again after 30seconds or so and I had it tilt trayed home. The no-crank fault seems intermittent but getting worse, the last few days it has been all 'no crank'. At first it would occasionally start and run a short time, but most often it has the 'no crank' behavior exactly as per using my old un-coded key. Every single other electrical device works perfectly even when it is in the 'no crank' mode - including the central locking remote! I only have a Foxwell scannner, but it will connect to all modules including the alarm, there are no faults* in any module, and when using either of my 'good' keys (both new genuine ones 2 years ago) the immobiliser status goes to 'Active' for about a minute after ignition-on, then changes to 'not active'. If I use the old key it is always 'not active'. So from this it seems the pill in the key is being read ok, and decoded and matched ok. Due to the behaviour of the old key I take 'active' to mean the engine should be active, rather than the immobiliser being active (ie preventing start). So at the software level the alarm module seems to be happy but maybe something goes awry on the output stage of the board? Thus far I have done the following; Battery tested and confirmed OK, also swapped another battery, no change. Check main electrical connections like battery- to body, body to engine, disconnect/reconnect both plugs in the engine bay, check main +ve lead to engine bay, and Y-cable to starter/alternator. This car has lived since 40,000km and 2009 in a dry part of Australia away from the coast and has zero corrosion anywhere. I inspected the fabled Y-cable during the rebuild and concluded it was fine. Ignition switch replaced with new genuine unit, no change. At one point it started and ran poorly and threw a bunch of codes that lead back to MAF. Last thing I did in the rebuild was clean and oil my BMF air filter. I swapped back to the original airbox/paper filter and cleaned the MAF with magic spray. Now it just threw an actual DME MAF error. Strangely, at that time regularly cranking fine. Got a new MAF (genuine Bosch) but since installation it has not cranked. I think MAF problems were a secondary issue from over-oiling the filter and were not related to the original stall/no crank issue. Now I actually started to diagnose rather than swap parts. I found a wiring diagram and traced back from the starter to the "Start Lock Relay" in the rear DME/relay area. The area is pristine, looks ex-factory. I had 12v on pin 86 (coil +ve) with ignition on, and 12v on pin 30 (contact input) with key in start position. I jumpered from pin 30 to 87 (contact input to output) and it would crank on the key but not start. From this I concluded it was not getting the switched ground on pin 85 which is listed as "O186 ME7" and "H114 CU DME" (ie the "computer says yes" signal). I can force that one but the DME still says NO. Swapped rear tray relays 1 (MFI-DI) & 7 (Start-Lock) which were identical, no change. Relay 1 (MFI-DI) appears to be energised all the time even with key removed. I would have thought that would switch on only with ignition ON. I'm still working to understand other parts of the wiring diagrams to see if that seems correct. Relay 7 (Start-Lock) DOES ACTUATE immediately after turning on the ignition, but switches off half a second later. If I mash the key direct to the start position, the engine briefly cranks before the relay opens again. So all the high-current side is fine. With Relay7 (Start lock) removed and probing pin 85 (the switched ground which actuates the relay) I get some number of Megaohms with key off, then a change when key goes on, but goes to open circuit. I would think that should go to more or less zero ohms, providing a ground to switch the relay. I lifted the passenger seat and inspected the Alarm module, there was a tiny evidence of a spilt drink or similar on the floor, but all wiring and the module looked mint. Removed the module and inspected the board and it looks mint to the eye, no corrosion etc. Reassembled everything, still no crank. So this is pointing to a DME or Alarm module problem but it seems so unlikely given it all fired up and ran perfectly numerous times over a period of a week after sitting for two years. And also that the car has not been subject to water leaks, corrosion etc which seems to usually bork the alarm module. The alarm module scans perfectly and I can see everything happening live like the immobiliser, door positions, windows, hoods, etc. Does anyone have any ideas of where a problem might arise other than the modules? Another relay somewhere? Are there any other tests I can run before pulling out the modules and sending them away? At least there does appear to be an Australian company (Injectronics) who advertises testing/repair, although there are a disturbing number of recent one-star reviews on google. The thought of having to replace the DME/Alarm/Keys at dealer prices terrifies me! Sorry for the long winded post, appreciation if you've made it this far... Steve

Hi when we rebuild our car we had a problem when the old keys were near the car the new keys would not start it, we had to take the old keys into the house, the pill was getting confused could this be happening to you. Took a while to figure this out.

Thanks Berni, I gave it a try but even with the old key in the house 30m away it is still in the no-crank mode. It seemed a rather forlorn hope anyway, given that the original failure was 10km from home during its registration test with no other keys in the car. At least it now seems to have completely failed, rather than being intermittent. Can the alarm module or DME be 'locked out' by disconnecting the battery with the ignition off? I have heard about always dis/re-connecting the battery with the ignition on, but must admit I haven't always done it. But that would not explain mine cutting out while driving, you'd assume if the car thought it had been stolen it would not allow you to drive it for 20 mins then die...

Calling Demort… (Demort was a forum Superhero that used to frequent these lands a few years ago, he’s a Porsche technician and may still respond to PM’s. He’s helped many of us with his detailed knowledge and was very generous with his time, by way of thanks some would donate to his preferred charity)

DeMort, yes I certainly recall him from my earlier times on the forum, I took a break due to lack of enthusiasm after the engine failure and once back I did notice that deMort was no longer around. Bummer for us, but I can totally understand if he needed to draw a line. He was so generous with time and knowledge it possibly ended up feeling like extending his work day into a night shift unpaid job as forum technical consultant! Meanwhile, Injectronics said that the part number of my alarm module only shows up twice in their records, both times water damage, both times unfixable. The DME showed up a few more times, including for no-start symptoms (maybe because they came in with the alarm module), so possible I guess. It still feels like the modules are unlikely to be the root of my problem, given they have not suffered any ill treatment and both scan with no faults. I have not found any evidence of rodent activity anywhere, which was my first thought as it sat in my garage for 18 months.

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Hi, Did you get the problem sorted ? I'm having exactly the same problem and same symptoms. .It will often start after going to sleep. But then same as you, the relays lose the ground signal from the DME, then no crank or start.

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Hi, unfortunately it is grinding on... Christmas delayed things while I waited for shops to re-open etc. I got some fantastic help from Richard Hamilton who I fortuitously stumbled upon via seeing some of his very astute answers to similar technical questions over on renntech. He provided me with correct 2004 wiring diagrams and a procedure for testing the one wire that runs from the alarm module to the DME for security purposes (W lead). That tested fine so it all pointed to a module problem (bearing in mind there are no fault codes in either the DME or alarm module). I already had Daniel at D-Parts in Melbourne in my sights as the next person to contact, and Richard also pointed me to him as someone right into all the demons of the electronic systems in these cars. He is also being fantastically helpful, I got a full set of 'loaner' modules from him and the car started right up. We flipped a coin and figured that the alarm module is more often problematic than the DME and it is also less work to recode and cheaper to purchase, so he then converted the loaner alarm module into a match for my DME. Unfortunately that returned the same symptoms as before, however we presumably narrowed it down to the DME. With the benefit of hindsight, this agrees with what I saw on the code reader, since I could monitor live values and see that the immobiliser seemed to be "working" in the alarm module, but not in the DME. I basically didn't want to believe the DME was faulty, partly because my mistaken belief that 'modern' automotive ECU's almost never go wrong for no reason, and partly because it was the most expensive part to go wrong so I reaaaly didn't want that to be the problem! I opened up the DME and let the electronics techs at work loose on it, inspected for any visible issues, reflowed joint between the W-lead pin and the board and tested continuity between the external pin and the board, which was fine. Reinstalling everything last night shows the same symptoms still. That's where I am at now, the next step is for me to send everything back to D-Parts and Daniel will return my alarm module with a newly reconfigured used DME matched to my VIN and keys etc. With luck and a prevailing wind, that will be the solution.

hiya, I have a somewhat related issue to you; I found a wiring diagram for the starter set-up. You can you check my thread for links to these diagrams. On the next dry day, I will check the power on the cables identified there. Perhaps you have some ideas for me. A Thread '997.1 not cranking and not starting, running out of options' 23 Feb 2025 Please help if you can, I've spent many hours today trying to figure this out, reading some helpful posts here, then checking and testing, and no luck. Porsche 997.1 2007 manual cab, with low mileage. It was working fine until the night before last. I went to start it, and it would not crank. 1. I turn on the ignition, and the dashboard lights up as expected; I turn the key further to crank, and it doesn't. The dashboard remains lit up and does not dim or change. 2. Turning the key to the crank position, the air con fan goes silent - suggesting the ignition key works. 3. releasing... austinc Replies: 26 Forum: Porsche 911 997 (2004-2012)

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Hiya, I received my modules back today with a good used DME rebirthed to match my car. The car flashed right up as if nothing ever happened, and I ran it for 10 minutes around my local roads and it is back to perfect behaviour. Big thanks to Richard Hamilton for the generous technical help, and Daniel at D-Parts in Melbourne for working through the diagnosis of the modules and supplying the replacement. Sorry to hear you have similar troubles, it's a most distressing time. A quick read of your thread and it sounds identical to my symptoms, which turned out to be a faulty DME resulting in the immobiliser never unlocking in spite of the key and the alarm system all working fine and disarming. My car was highish mileage (215,000km), but led a good life, car known to me since 2009, never got wet, garaged day and night, no fault codes, everything else worked etc. So there seems to be no real reason for the DME to fail, other than just poor original quality. When I have some more time I'll try to follow your links to the wiring and see if it has the same or similar arrangement as the 996.2. In my case I was able to crank but not start the car on the key when I jumpered the pins on the start lock relay. This allowed me to focus only on the immobiliser, since all the high current stuff including the starter itself was actually working. In mine there was one wire between the alarm and dme which carried the immo signal, so I could test that and find it was fine, which left only the modules. I believe for the 997's they moved the alarm from the puddle-collection-point under the seat to somewhere else, so they are not the automatic suspect they are in 996/986's especially soft-tops or sunroof cars. Although I seem to recall deMort saying that they then moved some other piece of electronics to that low point anyway, so didn't learn at all. Hope yours is something simpler than the dreaded modules! Cheers Steve