Error Code P0139
Moderate Issue
DTC Code P0139 indicates a slow response from the O2 Sensor Circuit in Bank 1 Sensor 2, where the Heated Oxygen Sensor (HO2S) takes longer than specified to switch between rich and lean conditions, affecting the air-fuel ratio monitoring.
What symptoms indicate Error Code P0139?
- Engine Light ON: The check engine light or service engine soon warning light illuminates, indicating an issue with the O2 sensor circuit. This is often linked to a slow response from the sensor, which can affect the engine's performance.
- High Fuel Consumption: The vehicle may experience increased fuel consumption due to the O2 sensor's slow response. This can lead to inefficient fuel-air mixture adjustments by the engine control unit.
- Excessive Smoke from Exhaust: There may be excessive smoke emitted from the exhaust, which can be a result of improper combustion caused by the delayed response of the O2 sensor.
What causes OBD code Error Code P0139?
- The rear heated oxygen sensor on Bank 1 may be faulty, leading to slow response times in the sensor circuit.
- An open or shorted harness in the rear heated oxygen sensor on Bank 1 can disrupt the signal transmission.
- Poor electrical connections in the rear heated oxygen sensor circuit can cause intermittent or weak signals.
- Inappropriate fuel pressure can affect the air-fuel mixture, impacting sensor readings.
- Faulty fuel injectors may lead to incorrect fuel delivery, affecting the sensor's performance.
- Intake air leaks can alter the air-fuel ratio, causing the sensor to respond slowly.
- Exhaust gas leaks can introduce additional oxygen, skewing sensor readings and causing slow response.
How to fix OBD code Error Code P0139?
- Verify DTC Code: Confirm the presence of DTC P0139 using an OBD-II scanner. Ensure no other related codes are present that might affect diagnosis.
- Inspect Oxygen Sensor Wiring: Visually inspect the wiring and connectors for Bank 1 Sensor 2 for any signs of damage, corrosion, or disconnection.
- Check Oxygen Sensor Operation: Use a multimeter to measure the voltage and resistance of the rear heated oxygen sensor. Compare readings with manufacturer specifications to ensure proper operation.
- Perform Exhaust Leak Test: Inspect the exhaust system for leaks near the sensor, as leaks can affect sensor readings and cause slow response.
- Evaluate Fuel System: Check for any issues in the fuel system that might cause a lean or rich condition, affecting the sensor's response time.
- Replace Oxygen Sensor: If all other components are functioning correctly, replace the rear heated oxygen sensor Bank 1 Sensor 2, as this often resolves the issue.
- Clear DTC and Test Drive: Clear the DTC code and perform a test drive to ensure the issue is resolved and the code does not return.