21 OXYGEN SENSOR SIGNAL/OXYGEN SENSOR HEATER SIGNAL
OPEN OR SHORT IN OXYGEN SENSOR OR OXYGEN SENSOR SIGNAL

It may have been the sensor but it may have also be the wiring to the O2 sensor heater circuit. If you replaced the sensor with a proper 4-wire unit, then look into the continuity of the sensor heater wiring between the sensor and the ECU.

And BTW, a bad sensor tells the ECU to run the engine rich to prevent possible damage and rich = high HC and high CO in the exhaust.

r.c.brown@ieee.org
TruckEditor@tlca.org
Project: 4Crawler
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