New O2 Sensor And Still Check Engine Light

[mattison]

I have a 1999 Gmc Suburban and can't seem to get rid of the darn check engine light. Original code says bank 1/ sens 1, so I put in a new sensor (aftermarket Bosch). Next day light comes on, bank 1/ sens 1 no activity, bank 1/ sens 1 heater circuit. Took the sensor back to the store (must be defective?), put on second sensor, same codes. OK, I thought maybe I could have a wiring problem with that circuit, so I swapped B1/S1 with B2/S2, now the code is gone from B1 but now I have a code with B2. Went to dealer and bought a new AC Delco sensor because after talking with their mechanic he said my problem was the aftermarket sensor and at three times the cost the AC Delco part would take care of my problem. WRONG! The new O2 sensor whether it be dealer or aftermarket consistantly shows 0.2mv lower than the other 3 sensors. Do I need to replace the other three to clear the code even if it's not the one showing a fault?