Error Code P0138
Moderate Issue
DTC Code P0138 indicates a high voltage condition in the O2 Sensor Circuit for Bank 1 Sensor 2, where the ECM detects the Heated Oxygen Sensor (HO2S) voltage exceeding 1,050 mV, suggesting a rich fuel mixture.
What symptoms indicate Error Code P0138?
- 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
such as a faulty O2 sensor or wiring issues. - High Fuel Consumption: The vehicle may experience increased fuel consumption due to incorrect air-fuel mixture readings from the O2 sensor. This can be related to
like a malfunctioning O2 sensor or exhaust leaks. - Excessive Smoke from Exhaust: There may be noticeable excessive smoke from the exhaust, which can be a result of improper combustion caused by inaccurate O2 sensor readings. This symptom is often associated with
such as a defective O2 sensor or fuel system issues.
What causes OBD code Error Code P0138?
- The rear heated oxygen sensor may be malfunctioning, leading to incorrect voltage readings.
- An open or shorted harness in the rear heated oxygen sensor can disrupt the signal transmission.
- Poor electrical connections in the sensor circuit can cause intermittent or incorrect voltage signals.
- Variations in fuel system pressure can affect the air-fuel mixture, impacting sensor readings.
- Contaminated fuel can alter combustion efficiency, affecting exhaust composition and sensor output.
- Faulty fuel injectors can lead to improper fuel delivery, influencing the sensor's voltage readings.
- Exhaust gas leaks can introduce additional oxygen, skewing sensor measurements.
- Engine vacuum leaks can cause an imbalance in the air-fuel ratio, affecting sensor performance.
How to fix OBD code Error Code P0138?
- Verify DTC Code: Confirm the presence of DTC P0138 using an OBD-II scanner. Ensure no other related codes are present.
- Inspect Wiring and Connectors: Check the wiring and connectors for the O2 sensor Bank 1 Sensor 2 for any signs of damage, corrosion, or disconnection.
- Measure Sensor Voltage: Use a multimeter to measure the voltage output of the O2 sensor. A high voltage reading indicates a potential issue with the sensor or circuit.
- Check for Exhaust Leaks: Inspect the exhaust system for any leaks that could affect the O2 sensor readings, particularly near the sensor location.
- Test Sensor Heater Circuit: Verify the operation of the sensor's heater circuit. A malfunctioning heater can cause incorrect sensor readings.
- Replace Rear Heated Oxygen Sensor: If all other components are functioning correctly, replace the Rear Heated Oxygen Sensor Bank 1 Sensor 2 as it is often the root cause.
- 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.