Repair procedures (plant/service)

0. Was the temperature drop caused by external factors (driving into snow pile, ice on O2 sensor?) Thaw sensor, clear all fault memory, continue driving!

1. Check O2 sensor heater: Contact resistance on plugs and in wiring is excessive (DME - wiring harness - sensor)
2. Check wiring
3. Check O2 sensor plug (water or corrosion in the plug? Repeatedly disconnect the plug and then re-insert it FIRMLY)
4. Replace plug and/or wire as indicated
5. Replace the affected downstream (post-cat) O2 sensor