P0139 1/2 Oxygen Sensor Slow Response

SYMPTOM
P-0139 1/2 OXYGEN SENSOR SLOW RESPONSE

WHEN MONITORED
With engine temp greater than 147 deg. F, after reaching a vehicle speed of 10 mph, and throttle remaining open (off idle) for 2 minutes, bring the vehicle to a stop and allow the engine to idle with the transmission in drive (auto) or in neutral (manual)

SET CONDITION
The oxygen sensor signal voltage is switching from below 0.27 volts to above 0.62 volts and back fewer times than required.

POSSIBLE CAUSES
- 1/2 O2 sensor ground circuit open
- 1/2 O2 sensor defective
- 1/2 O2 sensor terminal observable defect
- Exhaust system leaks
- Oil or coolant consumption
- PCM terminal observable defect