Diagnostic Aids

To locate an intermittent problem, using scan tool, monitor HO2S HEATER - LOW VOLT or HO2S HEATER - OPEN test after engine has been running greater than 45 seconds. When a fault (open or short to ground) exists, scan tool will display TEST FAIL for both tests.
Test updates every 100 milliseconds whenever engine has been running greater than 45 seconds and heater is commanded on via PCM.
Heater may be commanded on before first 45 seconds of engine run time if calculated converter temperature is high enough.
HO2S heater element resistance should be 12-27 ohms.

Fig 1: Identifying Heated Oxygen Sensor 2 Connector

Courtesy of GENERAL MOTORS CORP.