996.1 - Full electrical power - no crank / no start

Long time lurker/reader but unfortunately posting with an issue that I hope you guys can help with; Car has been starting, driving and running faultlessly. Used intermittently over recent months and on CTEK in garage when parked. Have gone to take the car out today, key turns easily with all electrical power and accessories operating as normal but no engine crank whatsoever. No other symptoms. Battery around 6 months old, no voltage drop. Previously had new Y cable. Searching the threads here I’m thinking it’s possibly the ignition switch - thoughts?? Looks like a little ***** to do and I’m mechanically inept but since I can’t even get the car out of the garage I may have to just give it a try but would welcome input on the problem first before I dive into that. Thank you

Clutch switch?

I don't think there is a clutch microswitch in the 996.1 (UK) ... pretty sure there isn't on mine. If it is the ignition switch, it's really not a difficult job as long as you remove the end panel from the dashboard. Took me under 2 hours.

could be starter relay, under carpet back of the car, it might be number 7 i can't remember off hand swap it with something else to test it.

Thanks for the replies so far. Yes, UK car so I believe no clutch micro switch. I’ve been back out and tried a bunch of times - no dice. Video clip attached.

Rusty earthing strap on the battery to the shell or the starter to the engine. Unbolt, clean it up with some abrasive paper and reattach.

After around 30 attempts, wiggling the key different ways, turning fast and slow, I managed to get it to fire. Am I right to assume this certainly now points to a failing ignition switch? I’ve gone ahead and ordered one from Heritage Parts since it’s the princely sum of about £11 and will set about trying to fit it in due course…

If it's the original switch, it almost certainly needs replacing anyway .. they wear out! Like I said, don't be put off by horror stories of how fiddly it is, because it really isn't! (Unless you try to do it all by lying on your back in the footwell without removing any trim!)

Thanks for the support! I’ve no spannering skills at all and less than dainty hands but will give it a go - I can’t reliably predict that I’d be able to drive it to the Indy in any case just now

Beware cheap switches. It is a common VAG part 4A0 905 849 or 4A0 905 849 B up to 2003 or 4B0 905 849 for 2004 onwards. Not too difficult to replace if you have smaller hands. Also note that the assembly is inverted on RHD cars compared to videos you may see for LHD cars. Access is actually easier on RHD from underneath and through the dash vent with a 2.5mm Allen Key, but don't take the grub screws all the way out or you'll curse lots when trying to get them back in. I did a 'How To' on another forum, but it has lost its pictures due to Imgur pulling out of the UK.

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Thanks - all noted. The part is MEYLE which I believe is an OEM and not a no-name Chinese part, I hope. I’ve watched a few videos tackling it from above and below so reasonably confident of what’s required now; are the grub screws slotted or Allen-head? I thought the former from everything I’ve seen…

Screws are slotted

Apologies, yes slotted. Some time since I did mine. Hex would have made it easier...

Guys - I’m at my wits end! Due to being away I’ve only just managed to attend to this and was rather pleased I got the whole job done in about an hour or so! In between times I’ve been able to drive the car normally a couple of times; once it took about 20 attempts before it miraculously fired as if nothing ever wrong. Last week it was a lovely day, I had a long journey and thought I’d try the Porsche on the off chance - it cranked first time no issues then drove perfectly for 3 hours and got parked up in the garage until I could tackle this job. However, despite being very chuffed with my efforts there’s absolutely no difference having replaced the ignition switch. Full dash lights, everything else seems to power up as normal but just nothing from the engine/starter. I guess I could have received a faulty part but is there anything else at all that I should be looking at here?? I would greatly appreciate any help and suggestions

Looking at some other threads again, the starter relay sounds like it is worth checking out - would this give intermittent issues as I’ve been having? My sense would either be it’s working or it’s not at all? Any pointers to access that relay - behind the back seats? Are there also any particular fuses I should check?

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yes it can stick, open or closed. intermittently

Thank you - will do some more research on accessing it. Assume I can temporarily swap with another relay to test?

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you can bridge the connection with a piece of wire, then turn the key the engine should turn over.

In most no start threads the relay is often mentioned, however I don't remember a single thread where it actually was the relay! I think it's a legacy from the 993 where it was a common problem! I've just guaranteed it will be the relay lol

Something else you could try. It's not only the electrical switch which can go wrong, the aluminium part of the barrel can also become faulty. The way to see if it's that is to undo the slotted screws and remove the electrical switch but leave it connected to the wiring, put the key in the barrel as it has the transponder chip in which needs to be next to the receiver which is mounted around the top of the barrel. Then use a screwdriver to manually turn the switch. The first turn should turn the ignition on and then if you twist further it should be spring loaded to the start position then it springs back to the ignition on position. If it starts reliably when you do this is means there is a fault with the aluminium barrel part!

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Really like this thinking - thank you. I will give this a go and report back!

Good tip, I’ve had to replace 3 or 4 ignition switches/barrels on cars over the years and this was definitely a problem on one of them, might even has been the 996.

Only just clocked onto this post. Could it be the immobiliser ? That's what the RAC said when they did a home start but failed to get her going. I've tried bypassing the starter relay behind the rear seat and next to the strut bolts but still nothing. Now booked in with Porsche specialist 13th April. Good luck with it

I’ve nothing to add to this thread except my sympathy - horrible problem to have and solve, good luck!!

Thanks for the support and suggestions. Will see what I can manage tomorrow ref the relay and testing of the switch again. Beyond that I’m well outside my comfort zone so have booked in with David Phillips in Edinburgh in anticipation of needing his expertise…

Update - mixed results. Picking up Mac996t top tip I disassembled everything (pro level at this now!) and removed the ignition switch from the barrel, leaving the electrical plug connected. Key in ignition to activate the transponder and then turned the plastic ignition switch with a flathead - dash lit, accessories on but no crank, same symptoms. So I guess that tells me the actual ignition barrel is not the culprit. Reassembled everything and gave the key a turn just to check it was moving freely after putting everything back and, surprise, started right up like nothing happened. Repeated this another 3 times successfully but on attempt number 4 - back to nada. Another bunch of attempts after that still nothing. So, seems unlikely the new switch is faulty nor as said the ignition barrel based on this sequence of events. What I did notice however was that on each time the car fired I could clearly hear what I presume was the fuel pump before the final turn on the key. When it then didn’t fire the same sound was notably absent. Is this now a big clue? I didn’t get the chance to check the starter relay behind the back seats - would this be the most likely culprit based on the above, or something else?

It’s got to be worth a try, the fuel pump must be downstream of the starter relay. Good luck, frustrating but an easy fix if it is that. .

I’ll look at the starter relay but I believe there’s a fuse and relay in the footwell for the fuel pump. Again, any suggestions around this would be really appreciated.

What's the history of the actual starter motor? The contacts in the solenoid can "burn" and provide intermittent starting.

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It’s had a replacement starter previously - a number of years ago but I don’t have the history to hand. Would a failing starter impact the fuel pump? I am assuming of course the low electrical hum I was hearing was in fact the fuel pump?

The fuel pump won't stop the engine cranking over. Are you getting a clicking sound at the engine when you try to crank it over? If not then you're not getting power to the solenoid , that could be a dodgy wire/connector , it could be at the loom plugs in the right side of the engine bay. If you are getting a clicking then it's a problem at the starter, either solenoid or motor. Also check the starter relay as mentioned before. At least you can eliminate the barrel /ign key switch You just need to check down the line for power

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Thanks. No click that I’ve obviously noted but will check this out - doing this solo but will see if I can enlist another pair of hands so I can listen carefully. Today was definitely the first I picked up on the distinct difference of something powering on (or not) which then allowed the engine to fire. I’ve equated it to the low electrical hum of the fuel pump hence that line of thinking. If there was a bad connection at the loom plugs would that prevent the fuel pump running? The intermittent nature of this is really frustrating. I’ll check the various relays first but at least now can rule out the ignition side of things as you say.

Ignition fuse, second in from the left on the middle row, green, 30A. (also check fuse 1 in this row as it is engine electronics) Ignition and engine relays are in positions 1 and 2 in Relay frame 2 adjacent to the DME not in the foot well.

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Thank you, that’s helpful. Will hopefully get time to dig into the fuses/relays before the weekend.

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Are you talking about the fuses in the footwell and the relays under the carpet nearside next to the strut mount

I had a very similar problem on my car about 4 years ago, I had a new power steering pipe fitted in the engine bay. After I collected the car all was fine then I took the car for an mot when we went to start the car there was nothing in the end after much head scratching we got the car to start did the MOT and I drove home switch the car off and tried to start it again nothing happened, I decided it was the starter motor so fitted a new one and still the same symptoms , I changed the ignition switch and still no change. I checked and changed some earth cables cleaned others up then went into the engine bay to the battery jumpstart point to find a loose cable on it. The specialist that fitted the power steering hose had disconnected the jump point and the when he reconnected it he failed to do it up tight hence the intermittent fault!

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Is there a diagram showing all earth points other than delving through wiring diagrams ?

Hopefully this makes sense

I had a similar situation, all electrics normal but no crank. Lots of diagnosis later it turned out to be the ECU. The alarm module was unlocking and sending the signal to the ECU but it was not disabling the immobiliser. You can hotwire the start relay which allows you to test the entire high current circuit, it still won't start but will crank if it's the immobiliser.

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Link to my thread... U Post in thread 'Two-year rebuild, now immobiliser issues?' 24 Feb 2025 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... Uber996au Hth

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Thank you - this is another interesting angle. I will have a read through your thread. Were the symptoms sporadic? I still get normal starts if I persist on some occasions.

The nice people from Porsche sent these today - hoping to tackle trial and error with the relays this weekend. Won’t do any harm to keep as spares in any case…

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Yes it started out somewhat sporadic, though a lot more 'dead' than 'alive' compared with your description. It first showed up while actually driving, then after 10 mins or so I could start it again and it ran normally for maybe 30sec then stopped again and wouldn't restart. Once home it worked on and off but mostly off for a couple of weeks while I was diagnosing and swapping parts. As my motor was fresh I didn't want all those short runs on it so I only waited to hear the starter or not and didn't actually start the engine. By the time I had worked through the ignition switch and MAF etc it was totally 'no-start' mode all the time. I didn't take a picture of the hotwire method, but you should 100% do that as outlined in my thread above. All it does is bypass the 'start-lock' relay which is normally controlled by the ECU (DME). As soon as you turn the key to the 'start' position it will turn the starter, regardless of alarm module or DME. If it turns over then it straight away rules out all of your 'high current' stuff - switch / starter / cabling etc -and focusses the problem to the immobiliser - RFID pill, receiver, alarm module, DME, or W-lead wire between them. Likewise if it still doesn't crank then it's vice-versa. If you can get hold of a basic Porsche scanner it helps a lot, I have a Foxwell and could see that the alarm module would recognise the key RFID pill and 'unlock' the immobiliser for a minute or so, but the DME never did. So I knew the alarm module was at least receiving a 'good' signal from the key etc. Once you get to your relays in your rear shelf the start lock relay should also briefly 'cycle' closed then open when you turn the ignition on. If it doesn't then it's am immo (or relay) issue. Hope it's not your DME, that's the most expensive problem. I managed to get a used boxster one reflashed with an image of my DME but it was still an expensive exercise.

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That’s really interesting. Thanks for sharing your experience with this; I’ll keep working through… Just my luck I didn’t fix this with the £15 ignition switch replacement!!

Here is a crazy idea. Push it. When the problem shows up again turn the ignition on and try an old-school push start. When you have a bit of speed bring up the clutch in second gear. Dip the clutch again if the car catches and runs. If the car starts using this method then you can rule our the ECU, immobiliser, and any ignition or fuel delivery compnents. At this stage it would be starter, relay or heavy cable related.

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I’d be happy to use this method of fault diagnosis but sloping driveway makes it very tricky indeed!

Guys, sorry for delayed response in updating this thread - I’ve had an accident (not car related!) which has involved surgery and basically being housebound with limited ability to use electronic devices. Right, so my specialist was unable to fully diagnose the issue and of course the car started each and every time while it was with them. Indeed, the issue has not reoccurred now for many weeks and dozens of start/stop sequences. I did have the car booked with the OPC but just last week was able to get some time with another specialist with regard to electrical system specifically and we had some more interesting investigation; Fault code 25 was the sole code held in memory but it was not clear when this was logged. Again, the car had continued to start every time faultlessly meantime using both keys… Porsche 996 fault code 25, often interpreted as "No terminal 86 S recognised," indicates a failure in the ignition lock system to signal the alarm module when the key is inserted or turned. This issue is often related to a faulty ignition switch, blown fuse E1, or wiring issues between the alarm control module and the ignition lock. Having changed the ignition switch already and still experiencing the same symptoms we ruled that out. Code was cleared and then by removing fuse E1 in the footwell we were able to replicate the exact symptoms again. Re-scanning showed code 25 logged again which confirmed that this was very likely to be what accounted for that first time around. There was no obvious issues with the fuse but it was swapped with a new one just in case. As the car continued to behave perfectly we did not go to the extent of stripping out the fuse box at this stage but there is a possibility that there is a wiring fault between the box and the immobiliser causing this issue intermittently. Of note, the same fuse also works with power to the stereo head unit and my man is of the firm view that the aftermarket unit installed in my car and/or previous associated wiring bodges that seem to be prevalent when stereos are fitted could well be the culprit here. So, not totally solved this yet and I’m very happy the car is now starting normally every time, but my plan now is to get the stereo out and replace it anyway and at the same time check every bit of wiring and address anything which might be suspect. I hope this is useful for others and gives some more insight. As always, I’d welcome views and thoughts from your assembled wisdom!

fuses can sometimes develop corrosion on the contact blades raising resistance. Often just removing and replacing them scrapes the corrosion off and Bob's your uncle, for no apparent reason everything works again. Might have been down to some condensation at some time. A thorough (or may be extreme) preventative maintenance option is, when you have the battery disconnected at some time, to go through pulling and replacing not only all the fuses but all the relays too to scrape the contacts in and out of their holders just in case you get that bit of corrosion again.

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Yes, that’s good advice. I’ll remain open minded meantime but equally optimistic that no more issues have arisen. I think checking the wiring to the stereo is still a sensible action too as I could certainly see how that is a high likelihood of introducing faults over the years.

Good result! Glad to hear you didn't have the same $$$ DME problem as I did!

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Not absolutely conclusive yet but keeping my fingers crossed! I’ll update the thread with any developments..

Following up on my previous posts on this thread, i have now had the car back and sorted. Mine didn't start nor was there any sound from the starter motor - turned key and nothing. It was the DME. Porsche wanted £2800 plus vat plus time with specialist to rectify. I found a local electronic company car Cartech Electronics and they cloned my DME and fixed the issue as a turn key for £588. So there are companies out there that fix electronic issues and prevent the throw away mentality. Hope this helps

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That’s great info, Roger - thanks for sharing. It is reassuring to know there are alternatives out there. Hopefully these posts/threads help others in the future too. You’ll be delighted to have your car back to full health

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Just stumbled across this thread - any luck with yours? I just bought another 996 and having a similar problem. All power functions work except ignition. I am able to start it from jump leads/battery pack but zero clicking or attempt to crank without. Fuses all fine…..

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Rusty earthing strap on the battery to the shell or the starter to the engine

Had exactly the same problem on my 997.1 Rust on cables can prevented the necessary current to start the car

Definitely worth going over the entire starter cable from front to back , just checked mine on the bulkhead this week ...not good. Amazingly that bolt came off with a 1/2" socket, I'm making up a new + cable from battery to the post.

1/2", a seriously rusted 13mm then!

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Looking similar here

Earth Strap! I'd check under the heat shrink at the terminals particularly the engine side to see if the cable has started to break.

Tearing my hair out with mine now. Got that strap off, cleaned up the ends (have ordered a new one anyway) and resistance is nice and low. Had battery tested - fine. Invoices show a new starter last year. Replaced ignition switch It will occasionally start with a battery pack or jump leads but one thing I noticed is that I get no sparks when attaching jump leads. Also, on other cars my battery pack will beep when I turn key to first position to tell me it is ready to start but it isn’t doing this here. Immobiliser/key transponder? (Remote locking working fine) Might try that engine/earth strap again and polish up the frame it’s earthing to a bit more. No water damage to box under passenger seat. Only diagnostic fault in getting is “DME passive/sporadic voltage supply - code 108” which I think is just from disconnecting the battery….

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Thanks! Got a new one made up by my local auto supplies - £13. And so far.... it works... don't want to jinx it. And yeah, the old one is f*****

WOW! that's bad...worse than mine. I think it's the engine end as it's moving around a lot more than the other end especially when engine mounts are shagged. £13!

That IS bad! Copper can get brittle with age and add some moisture; sure don't help...