Markn23 Posted June 7 Share Posted June 7 Engine will not run after a very comprehensive investigation and replacement of various parts and sensors the cause seems to be the immobilizer not communicating with the ECU . looking for information with regards to the what the current should be to the ecu from the 5SA ( seems to be pin 13 on the MEMS 1.9 unit ) to confirm this issue ( only using a basic meter ohms / Volts etc) I know there has been a lot of discussions on the 5AS and the modification for it to be used with out the disarming key fob ( ive never had a key fob ) . It appears my system was hacked before my ownership 6+ years ago , what interests me is why has it changed , would a voltage spike from either the battery master switch or a faulty ignition switch cause this or an intermittent problem on the earth of the 5AS . I also notice that a number of wires from the 5AS go to the OBD port would using this have an effect , I realise that the 5SA / ECU can be modified again and would like to have this done again , but concerned that it might happen again , suggestions and past experiences welcome Link to comment Share on other sites More sharing options...
Wrightpayne Posted June 7 Share Posted June 7 Try searching for posts by Revilla - he has done lots of work understanding how the Rover ECUs work. Link to comment Share on other sites More sharing options...
revilla Posted June 7 Share Posted June 7 Hi, heard my name mentioned ... You can't really check the communications line between the 5AS and thr MEMS1.9 with a multimeter. It's a coded digital square wave signal. You need a logic probe or an oscilloscope really. How exactly was yours modified to run without the immobiliser? The 1.9 doesn't actually have a flag in the map to tell it not to look for an immobiliser (well, it may have, but you can't write to the map on them to change it so it effectively doesn't). What it does have is a sort of factory learning mode. In this mode it is looking for a valid immobiliser signal and when it sees one, it learns it and locks to that immobiliser. That made it easy to pair them up in production, you just put one MEMS1.9 and one 5AS in the car and they pair when first powered up. I think what people have tended to do as a hack is to put the ECU into learning mode and then cut the wire between the 5AS and the MEMS to make sure it never sees a signal. They often cut the pin internally, inside the ECU case.That way it stays in learning mode forever, and in that modenit will run. In theory! The problem is they have been found to occasionally interpret random noise picked up on the cut immobiliser line as a 5AS signal, learn it and lock onto it. That leaves them permanently immobilised. Actually grounding the pin rather than just cutting it and leaving it floating would be a safer bet I think. If that's what's happened, then you need to put the ECU back into learning mode. There are several tools out there that can do that, but none of them are probably worth buying for a one off. I've got the tools, if you wanted to send me the ECU an 5AS I could have a good look on the bench to see what's happening and sort them out for you? The other alternative is ... I'm just in the process of adding in all of the basic diagnostic features for MEMS1.9 into my MEMS3 tools suite. The full thing is not ready to go yet, but I could easily knock up a little Windows program that would just put the ECU into immobiliser learning mode. All you would need then would be a £7 cable off eBay. Let me know if you want me to help! Cheers, Andrew 1 Link to comment Share on other sites More sharing options...
revilla Posted June 7 Share Posted June 7 Just a thought. There was another trick that people did. This one involved cutting a different wire. It's like diffusing a bomb! Some immobilisers had "passive arming". I'd yours has a MEMS1.9 it may be too early for this but maybe not, I think it came in for the 1997 model year. On those, if you didn't set the immobiliser on the key fob, it would start a countdown timer when you turned the ignition off and set itself after a period of time. There was a flaw though, the immobiliser had two power supply wires - one ignition switched, one permanent 12V. If you cut the permanent 12V supply, then when you turned the ignition off the whole immobiliser lost power and shut down immediately. So it never got to do the countdown and never armed itself. If that's how yours has been done, it could have somehow inadvertently armed itself again. Do you actually have key fobs for it? If so, worth seeing if you can disarm it on the fob, and it may then stay disarmed. Link to comment Share on other sites More sharing options...
Markn23 Posted July 9 Author Share Posted July 9 Update : A big thank you to Andrew Revilla for all his assistance and knowledge to resolving this problem in brief the cause of the issue was with the MEMS ECU having a internal fault and a faulty connection in the ecu connector and not the Immobiliser Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 9 Member Share Posted July 9 On 07/06/2024 at 08:58, revilla said: On those, if you didn't set the immobiliser on the key fob, it would start a countdown timer when you turned the ignition off and set itself after a period of time. There was a flaw though, the immobiliser had two power supply wires - one ignition switched, one permanent 12V. If you cut the permanent 12V supply, then when you turned the ignition off the whole immobiliser lost power and shut down immediately. So it never got to do the countdown and never armed itself. "Andrew is the champion!" Jonathan Link to comment Share on other sites More sharing options...
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