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Checking Oxygen Sensor Heater

Tests 1 - 4:

Tests 5 - 8:

SYMPTOM
CHECKING O2S HEATER

POSSIBLE CAUSES
- Downstream O2 sensor defective
- Upstream O2 sensor defective
- ASD relay out circuit open (downstream)
- ASD relay output circuit open (upstream)
- Heater ground circuit open (downstream)
- Heater ground circuit open (upstream)