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 engines has been running greater than 45 seconds and heater is commanded on via PCM.
• HO2S heater element resistance should be 12-27 ohms.

Check sensor and PCM connection for corrosion. Check for proper terminal connections. Comparing reading to a known-good vehicle with the same sensor is a good way to check accuracy of suspect sensor.