P0138 - O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 is a generic powertrain diagnostic trouble code indicating O2 Sensor Circuit High Voltage Bank 1 Sensor 2. It relates to the Fuel & Air Metering system.
DTC Breakdown (SAE J2012)
| System | Powertrain (P) |
| Type | Generic |
| Subsystem | Fuel & Air Metering |
| Fault Index | 38 |
| Standard | SAE J2012 / ISO 15031-6 |
What does diagnostic code P0138 mean?
The engine control module logged P0138 because it detected a high voltage in the oxygen (O2) sensor circuit for Bank 1, Sensor 2.
Severity Level & Driveability Details
Severity: Moderate
The engine cannot adjust fuel mixtures properly, leading to poor performance, low fuel economy, and potential catalyst damage over time.
Common Symptoms of P0138
- Check engine light illuminated.
- Poor fuel economy caused by incorrect oxygen sensor feedback.
- Engine stumbling, rough idling, or minor hesitation.
- Failing tailpipe emissions test due to incorrect exhaust feedback.
Typical Causes for P0138
- Failed oxygen sensor (Sensor 2 on Bank 1).
- Corroded wiring or loose electrical connector at the sensor plug.
- Blown O2 sensor circuit fuse.
- Exhaust leaks near the oxygen sensor location, introducing unmetered air.
Diagnostic and Troubleshooting Steps
A normal upstream sensor should oscillate rapidly between 0.1V and 0.9V. Monitor O2 sensor voltage output on a scan tool. If the signal is stuck or slow, verify reference voltage and heater resistance with a digital multimeter.
Typical Repairs and Fixes
- Replacing the oxygen sensor (Sensor 2 on Bank 1).
- Repairing damaged wiring harness or connector plugs at the sensor.
- Replacing the blown O2 sensor fuse.
- Repairing exhaust leaks near the sensor.
Sensor Location & Parts Involved
The oxygen sensor is located in the exhaust pipe, either upstream (Sensor 1) or downstream (Sensor 2) of the catalytic converter.
Clearing Code & Recurrence
Clear the code using an OBD2 scanner and perform a drive cycle to reset the monitors.
Emissions & Smog Inspection Impact
Can cause rich running (excess carbon monoxide and hydrocarbons) or lean running (excess nitrogen oxides).
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Related Diagnostic Codes
Sources & References
This diagnostic guide is compiled and verified against the following authority sources:
- EPA Emissions OBD Guide
- SAE J2012 specifications
Frequently Asked Questions about P0138
What does the Bank 1 Sensor 2 O2 sensor high voltage code P0138 mean?
The engine control module logged P0138 because it detected a high voltage in the oxygen (O2) sensor circuit for Bank 1, Sensor 2.
Is it safe to drive with the Bank 1 Sensor 2 O2 sensor high voltage code P0138 active?
Yes, but engine fuel efficiency will decrease until the sensor is replaced.
How much does it cost to repair a Bank 1 Sensor 2 O2 sensor high voltage code P0138 fault?
Replacement parts cost $80-$200. Labor to replace the sensor is $70-$150 depending on rust and access.
What are the common causes of the Bank 1 Sensor 2 O2 sensor high voltage code P0138?
Trigger conditions for the Bank 1 Sensor 2 O2 sensor high voltage code P0138 include: Failed oxygen sensor (Sensor 2 on Bank 1)., Corroded wiring or loose electrical connector at the sensor plug., Blown O2 sensor circuit fuse..
Can I clear the check engine light for Bank 1 Sensor 2 O2 sensor high voltage code P0138?
Clear the code using an OBD2 scanner and perform a drive cycle to reset the monitors.
Will the Bank 1 Sensor 2 O2 sensor high voltage code P0138 cause an inspection failure?
Can cause rich running (excess carbon monoxide and hydrocarbons) or lean running (excess nitrogen oxides).