O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
The P0138 code indicates that the oxygen sensor located after the catalytic converter (downstream) on Bank 1 is reporting a voltage signal that is higher than the expected range (typically above 1.0 volt). This sensor monitors the efficiency of the catalytic converter by measuring oxygen content in the exhaust. A high voltage reading suggests a rich air-fuel mixture or a sensor malfunction. Common causes include a faulty oxygen sensor, wiring issues, exhaust leaks, or a failing catalytic converter.
01. Most Common Causes
- Faulty oxygen sensor (Bank 1 Sensor 2)
- Short circuit or damaged wiring in the sensor circuit
- Exhaust leak before the sensor
- Faulty catalytic converter
- Engine running rich (fuel system issue)
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Poor fuel economy
- Failed emissions test
- Possible rough idle or hesitation
03. Step-by-Step Diagnosis
Step 1: Scan the vehicle for codes and record freeze frame data.
Step 2: Visually inspect the O2 sensor wiring and connector for damage or corrosion.
Step 3: Using a multimeter, check the sensor voltage signal at idle and under load; compare to specifications.
Step 4: Check for exhaust leaks near the sensor using a smoke machine or soapy water.
Step 5: If sensor and wiring are okay, test the catalytic converter efficiency with a scan tool or backpressure test.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
You can drive short distances, but it may cause poor fuel economy and potential damage to the catalytic converter over time. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Replacing the oxygen sensor typically costs $50-$150 for parts and labor. If the catalytic converter is faulty, replacement can cost $500-$2,000.