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Pin 66 on DME is not closing to ground to enable the ACTUATION-START-LOCK relay

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LHD, Tiptronic, 1998 Carrera Coupe


Hi all, new to the forum but I was consulting some existing threads in the public forums regarding similar and related issues before I started an attempt at this job. I have access to the full wiring diagrams for the vehicle, the pdf is "996 Wiring 1999-2000.pdf" and can be found on google. I had them printed out on large sheet paper so I could trace the wires and go through all the possible issues without having access to factory scanning tools. I'm an electronics and industrial instrumentation technician hoping to build more work experience and reputation in order to get access to more of these repair gigs in the future on higher model cars.


I am working on a 1998 Carerra (Japan market) that was installed with a 'fancy' alarm system that sat on top of the existing setup and most of it was removed prior or at delivery, and I spent yesterday inspecting and repairing the wiring harness from the hack job that was previously in there. Today I went through the troubleshooting steps in order to eliminate probable causes of a no-crank.


The current owner had ordered a new ACM (alarm control module) and had it re-programmed and had told me the porsche dealer said to him the reason it won't start is a 'wiring problem' which I believe I had repaired all the wiring so far in the vehicle. I still have the old ACM with the car, it's just un plugged in the front storage.  After doing my troubleshooting today, I believe it to be the DME but my lack of understanding how the modules interact I'm not sure if it defective or just needing to have some re-programming of some sort which may require a porsche scan tool.


Here's a take-away from my notes today;


Check for B+ signal from ignition start to pin 30 on START LOCK RELAY SUPPORT REAR when ignition key set to START. B+ present

Jumper pins 30 and 87 to test the relay is working. Turn ignition to START and check for engine cranking. Engine cranks.

Check for B+ from pin 86 to the relay coil. B+ present 

Ground pin 85, and turn ignition to START. Engine cranks. Relay is working.

Check for current path from pin 85 on the START LOCK RELAY SUPPORT REAR to the DME connector pin 66 ACTUATION START LOCK. YEL/VI/BR wire. There is a path. PIN 66 on the DME is not switching to ground, and this won't let the car crank and start.


Check for path of ground from DME pin 68 START LOCK to the shifter PARK and NEUTRAL. It grounds in each position, open in any other.


Check for B+ on pin 88 on the DME which is the DIAGNOSIS W LEAD, and the only wire from the alarm leading into the DME. From my understanding of the alarm system from reading the description of operation from my ALLDATA catalogue, there must be some sort of handshaking going on between the RFID in the key fob, the correct serial and cypher in the ACM and the DME in order for this pin 66 to ground to let the car start.

Checks at 7.37V with the DME dis-connected, and 8.34V with the DME plug end connected. I also ohmed out this wire 0.2ohm to check for any unusual resistance because seeing that voltage struck me as unusual. Again, I'm not sure of how this system interacts but I can only assume it's correct as I also tried to measure this voltage with the spare ACM installed with the same reading.


What I wanted to ask for;

Is this a wiring problem, problem in the ACM or DME and what would have to be done to rectify it.


Warm regards, Aurelius


Attached are three helpful photos of the DME ACM and a sheet that I believe came with the new ACM




Edited by Loren
I removed your IPAS codes - so no one can steal your car.
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All those tests you did were good and they show that the problem is the immobilizer. For some reason, it's not happy so the DME is not grounding the starter relay.


A few questions:

- Have you tried other keys?

- Are the transponders inside the key fobs and are they secured inside the fob?

- Any CEL?

- Checked fuses C1 to C4 and E1?

- Is there a fuse on the immobilizer  I forgot about it)?

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Hi. Unfortunately I don't have a Porsche or access to a durametric scanner. :drive1:


I do have a generic scanner, do you know how I can get it to work though ? I tried before and it seems like it can get connect but that's it. It won't work completely if you know what I'm saying. However it is claimed as compatible with porsche 996


There's only one key, as far as I know.


I read in the description of the Anti Drive off Feature

"The anti-drive-off feature is activated when the alarm system is armed. If an alarm is triggered, terminal 15 for the DME control unit is interrupted and the ignition and injection systems are disabled."

(obvious that DME pin is wrong though) 


I havent checked those fuses you mentioned - it's a good suggestion but I am not sure how these would interact to trigger the computer's anti-drive-off function.

 Wouldn't the engine just crank and not run if these fuses were open ? I can check and get back to you tomorrow. And there is a fuse on the ACM and it's closed.


I would like to tell the owner if he should tow the car back to porsche and have them re-program the system, or if it would be worth it to buy a duramatric scanner. He mentioned it would cost him over $1000 to have porsche do some service (although this could have been the cost for a technician to repair the wiring harness) 


What's you opinion on the print-out sheet that I attached that come with the ACM ? Does it mean anything to you ? 

Edited by aureliusmaxed
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Do you think it's worth it to close the drivers door and arm the system to check for the flashing of the alarm readiness lamps ? After ten seconds if all its inputs test good, the readiness lamp will flash rapidly. 

If faults are found, the lamp will not flash during the check period of ten seconds. A fault condition is displayed by double flashing after the check has been terminated.


However, I'm not sure if this would cause a no-crank condition, as the system is dis-armed when I'm working on it (I believe)

Edited by aureliusmaxed
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  • Admin

I removed your IPAS codes - please do not publish those here (or anywhere else for that matter).


1. Do you get one or two beeps when you lock the car?

If you get one beep then you have an alarm zone open.

If you get two beeps then you have an alarm fault. If this is the case you will need a Durametric tester or a Porsche PIWIS tester to diagnosise further.

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Some of those fuses power the DME and the alarm. If E1 is bown, the car won't crank but the CEL should be tripped though.


A generic OBDII should be able to connect to the DME, read obdii codes, and query emission readiness, etc. If the scanner is good then it's possible the DME and/or the alarm is the issue because the OBDII scanner talks to the DME via the alarm.  Without Durametric or a Porsche scanner, you are pretty much stuck.





Edited by Ahsai
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Sounds like you work in a shop so I think the Pro version makes a lot more sense. Otherwise, you can only use it on 3 Porsche.

One more comment since the Pro version will be more investment. Even though Durametric will show you the error codes and gives you more clues, it's only a starting point and there's no guarantee it can pinpoint exactly what the problem is.


Also, if you want to eliminate the DME and immobilizer as the source of the problem, you can check with ecudoctors.com I believe they can diagnose your units if you send the pair and the keys to them.



Edited by Ahsai
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so i checked the four fuses good, and the orange power wire going to connector I pin 16 of the ACM and I get B+. there was one DTC and it was P0600 which I cleared and it didnt come back last on/off cycle with the ignition. it may have triggered as I disconnected either a DME connector or alarm connector while the ignition was on, perhaps.
when i hit the lock button on the key making sure all the doors and hood closed i get one beep and two flashes on the key LED. i can open the driver door once its armed and the siren will go off. which means the alarm module not sending a signal to the lock solenoid. when i press the lock button twice i can then open the door without a siren, where after the alarm siren blips once.

Sent from my iPhone using Tapatalk

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the P0600 was triggered with the ignition ON with ECM plug removed. just as I suspected, by reading up the code. now that i cleared it, its not coming back. thanks for the replies ! ill be looking into why the central locking system is not working. the key icon on a rocker switch in the centre console is doing nothing when i assume the doors should work.

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hi all. a little update. since the central locking did not work i wanted to isolate a switch, path of current to the wires or eliminate a fault in the ACM.

attached is a photo of the diagram with my comments that proved the wires and switch are good and i also tested the LED forward voltage. so the switch is good, but alarm module does not respond to the trigger signals. i jumpered pins 4, with 2 and 1 separate to test its function.

what does this mean and can we confirm a faulty alarm module here ?? 2a885be9c7b52abe7c836d891f7aca32.jpg

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There are many microswitches involved and you desperately need Durametric. My guess is one of the microsiwtches is bad and not detecting the doors are closed so the alarm doesn't try to lock the doors.


Regardless, your no crank situation seems to be independent to this central locking issue.

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1 hour ago, Loren said:
It might be time to open the alarm module and see if it has water damage and/or corrosion. (IMHO)


hi. the owner claims to me he bought a new unit which porsche dealer had programmed . i believe him but will open and inspect for obvious defects to the PCB

bought a durametric to further diagnose any potential causes of failure

Sent from my iPhone using Tapatalk


Edited by aureliusmaxed
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  • 3 weeks later...

Great. So finally the durametric enthusiast scanner had arrived along with my 16ft active usb cable extension. I have tested for fault codes and determined the following


Bosch Digital Motor Electronics Motronic 5.2.2  
  Module Identification
Part Number      996.618.610.04 
Supplier Part Number      004155073701 
  Current Fault Codes  
Supply voltage Open circuit
 Alarm I32  
  Module Identification
Part Number      996.618.260.07 
Supplier Part Number      080504003007 
  Current Fault Codes  
Central locking limit position Unlock not reached
Status: present 
Occurance Counter: 1
W lead (DME immobilizer)
Status: not present 
Occurance Counter: 1
This fault is displayed for informational purposes, it is not an indication of a problem and no repair is needed.
Wrong door lock module
Status: present 
Occurance Counter: 4



After I cleared the fault codes and re-connected the scan tool and tried again to start the car, I didn't notice again any new fault codes. I think these codes were just stored when I had disconnected modules with the key set to ON. 


Excuse my possible mistakes as I am learning this program. I ran a 'short test' after clearing all the codes. This is my new result;

Short Test  
Bosch Digital Motor Electronics Motronic 5.2.2
Current Fault Codes  
Supply voltage Open circuit
  Alarm I32
  Current Fault Codes  
Wrong door lock module
Status: present 
Occurance Counter: 1

Edited by aureliusmaxed
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P1602 indicates a loss of power to terminal 30 of the DME, which will erase all adaptation values stored in the DME.  Usually, this is a wiring or DME connector issue, and rarely a DME fault.  That alone is going to aggravate the Hell out of everything.

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Alarm fault code 21 is "Short circuit to ground/open circuit in the communication lead between the alarm system control module and the DME control module"

- Plug A pin 23


Although it doesn't show up after reset, it sounds very suspicious given the DME doesn't close the start lock relay.


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thanks for the input ! i'm currently tracking this down.


Following the troubleshooting guide from alldata, I've tested pins 26 on the Tiptronic computer connector AND the DME connector. Both show a strong 12.47V with the ignition off. Resistance shows 0.5 ohm to B+. 




Looks like a new transmission control module should be ordered or sent for repair. Any thoughts ? 


Edited by aureliusmaxed
the proper attachment this time
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I've been trying to reach ECU doctors in florida. I have attempted to call their 1800 number which seems as if it is disconnected when calling from canada. And they have not replied to my contact form email I sent them over two days ago. Any one want to give an opinion ? 

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