Trouble is now, 1 Tester says its OK, No fault found, Another Tester now says its faulty.

That would leave me with too much doubt, Who's right, Who's wrong. ??

Is the First Tester not testing them properly, ?? Is the second Tester Trying to make a quick Buck ( or £500 Bucks )

Unless another ecu is fitted, You may never know the truth.

This is why you have to make a decision on the vehicle and then stick your neck out and buy the part that you think is faulty. ( you will never be 100% sure, but you can be 90% if youve done a reasonable amount of testing.

Best part about GM is they are Popular and if you fit a part and it doesn't cure it, You can fit it on the next one that comes in.

Try Autovaux on 01924 376003 for a new ecu.