This will start when it feels like it and will just crank at other times. Often it will fire up and die seconds later just like an immobilised VAG Car.
Each time it will throw
720A - Communication Between PCM & Immobiliser Faulty. The fault sets at Ignition on before cranking.
PCM & Immobiliser power supplies, connector pins are tight and shiny like new.
I have taken 2 wave forms at Pin 4 Immobiliser unit, one with it unplugged and I believe I have 2 way communication.
check immo coil/immo module for bad soldering,bad contacts.
I did check the Module connector contacts, but did not open the box. I can tomorrow.
As for the Immo Coil, the antenna for the transponder - I have read that these are a very common failure. However I did not go towards that because of the fault code description. Cutting the Signal wire from ECU to Immo Module gave me the exact same fault code hence my attention was focused only on the 2 modules and that wire.
At the point that I could see, or guessed that 2 way communication is taking place it was time to stop and ask for help or give the job to a more capable technician. I don't have Vida for diagnosing this but I have just placed an order to purchase it.
I have just looked at the Fault code table in KTS and I see that there is only one Immo code listed. Or is this a shortfall in KTS ??
Is it the case that in these older cars that they covered any failure in the entire Immo system with on code ???
This diagnostic trouble code (DTC) indicates that the configuration between the engine control module (ECM) and the immobilizer does not correspond. The immobilizer transmits the VIN code to the engine control module (ECM) at start attempt. Diagnostic trouble code (DTC) ECM-720A is stored in the engine control module (ECM) if the engine control module (ECM) interprets the code as faulty or missing. The engine control module (ECM) will not allow the engine to be started.
To be precise this car is MY1999 and not MY2000. It doesn't change much but still.
Indeed it was registered as new here in the Uk in 1999. However when I went looking for Factory Wiring Diagrams on Google the 1999MY did not match so I 2000MY and they did match. It was a few days ago now.
And there is a typo in that VIN. first letter (shoulb) should be Y not V
Indeed, well spotted and I stand corrected, that should be a Y not a V
Do you have any codes in IMMO module (not ECM)?
KTS & Snap On is all that is available to me (I forgot about Autocom) and no they do not delve into the IMMO as much as we would like.
What's the immo related history of this car?
Regular customer, known to us. Reliable Information is that it can not be relied upon to start. Sometimes it could be fine for a week other times not. It was fine for at least 5 days in the workshop, it would start several times a day.
Then it would not start for 3 days, after taking the captures with the scope which involved removing the IMMO and plugging it back in it started. Beating the IMMO box with a screwdriver handle had no effect, it continues to start for now.
I have only one key and remote for Central Locking which is not working and the man is not complaining about that.
I will have the use of VIDA in a few days, then I can look at Live data etc. to get a better understanding.
Thank You for the information - Very Kind - I will reply again when I have more.
Last edited by STC on Fri Aug 18, 2017 5:57 am, edited 1 time in total.
The immobilizer transmits the VIN code to the engine control module (ECM) at start attempt.
I disagree. It does so at Terminal 15 Switch on, not before or after. From what I have measured.
Maybe. This is a quote from service manual. And it depends what someone defines start attempt to be.
Anyway this DTC mean that there is communication error between ECM and IMMO. Don't know whether it's real communication problem or just data doesn't match.
Looking at live data in ECM and IMMO can steer you in right direction. Also fault codes in IMMO (which Autocom should handle). If there is problem with reading a key then this ECM fault code should not be stored.
Today it was immobilised again. It fires up and cuts out, eventually just cranks.
I did get Autocom on it tody and found codes in IMMO for Transponder & Key. 720A I believe sets at the same time in PCM. No spare key is avialable so I think I should look at the antenna next.
I took some captures today.
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