My name is XXXXX XXXXX I am a professional here at Just Answer. I noticed that your question was not getting a response and thought I would ask to see if you still need help with this.If the alternator was outputting high voltage like this here it is possible that this has damaged the ecm itself as I have seen voltage surge/spikes will cause an issue like this here.Usually you would see more then the 4.9 volts for voltage with this code but if the ecm is internally spiking intermittently and is damaged it can cause this.I would double check all 5 volt references to make sure none are shorted to voltage anywhere before replacing the ecm.Make sure you have no faulty or damaged wiring,make sure the electrical connections on the engine are tight as well.I hope this has helped in some way here.If you need anything else don't hesitate to ask thats what I am here for.If you are not satisfied with my help here let me know before rating my help.Thanks Pete
thanks for the reply
i have only checked the reference voltage at the MAF plug and at the MAP plug, I assumed there is only one reference line that is common to all sensors?
Ive checked as much as i can for wiring damage etc.
Initially i had this fault after the van had been sat for a period of time and the battery died. I fitted a new battery, started it up and immediately had fault lights and limp mode.
yes there was several undervoltage type faults which all reset, then i was just left with this fault which would not reset.
I have tried the battery trick before, but I will try it again. It does seem like it is an ecu fault, I just wanted to be sure really.
Thanks very much for your help.
One last thing, if I were to get a new ecu from VW would it come ready to plug and play? or would it need to be coded with a laptop?