P0134 Oxygen sensor no output.
P0170 Fuel system trim rich.
Sensor replaced(twice) with correct NTK part. Faults return after a few days use.
Customer complains of a hesitation, usually when cold. We have not experienced any drivability problems.
Sensor switching appears normal on Tech 2 live plot.

TIS for P0170 says sensor rich for 60secs.
TIS for P0134 says no sensor output.
Checking procedure says to check O2 harness pin 2 voltage with Tech 2 or DMM, sensor disconnected. Tech 2 switches 410 to 429mv(one or other at random). DMM 420mv. TIS says if less than 450mv short between sensor and ECU or ECU faulty. Disconnecting engine side of ECU, Tech 2 same readings.

Only logic I can draw from this is a faulty ECU. Anyone been here before?