i did a free diagnostic check up on a vectra last week and the ecu light was on
front lambda was not pulsing properly at all even though in closed loop
ecu code was rear lambda as it was dead
when u revved car evident misfire at low revs then front lambda starting pulsing briefly
found it strange front lambda was not flagging
further diagnostic work by me found the harness had come lose and lambda wiring melted due to it touching the heatshield / downpipe
told him to replace both lambdas