P0138: Oxygen Sensor Circuit High Voltage (Bank 1, Sensor 2)

written by Edmunds.com^{This story was created with generative AI and was reviewed and fact-checked by our staff of editors and experts.}
edited by Carrie Kim^{Creative Services Project Manager
Carrie Kim has been writing about cars for well over a decade. No matter if she's cruising with the family or chasing down her next breakfast burrito, she's (not so) silently judging car infotainment systems, interior color palettes, and dashboard finishes all along the way. She's a big fan of massaging seats, adaptive cruise control and wireless CarPlay. Over the years, she's particularly enjoyed helping parents find their own unique family wagons.}
11/15/2024
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Understanding P0138

The P0138 error code means "Oxygen O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)." This code appears when the engine control module detects a high voltage signal from the oxygen sensor on Bank 1, Sensor 2. This sensor measures the oxygen levels in the exhaust after the catalytic converter to help manage emissions.

Why it's important to address P0138

The P0138 code is important to address because it indicates a problem with exhaust gas monitoring. An abnormally high voltage reading often means the engine is running too rich, which can lead to increased emissions, poor fuel efficiency, and potential damage to the catalytic converter over time. If unaddressed, these issues may lead to costly repairs and reduce the vehicle's performance.

Can I safely drive my car with this error code?

Yes, you can typically drive with the P0138 code, but it's advisable to get it repaired soon. Driving with a rich-running engine can lead to higher fuel costs, increased emissions, and potential long-term damage to the catalytic converter, which is expensive to replace.

Common symptoms of P0138

Check engine light is on
Increased fuel consumption
Rough idling or stalling
Poor engine performance
Strong exhaust odor due to rich fuel mixture
Failed emissions test

Diagnosing P0138

To diagnose the P0138 code, technicians generally follow these steps:

Scan for codes: Use an OBD-II scanner to confirm the P0138 code and check for any related codes.
Inspect wiring and connectors: Check the wiring and connectors for the Bank 1, Sensor 2 oxygen sensor for signs of corrosion, damage or disconnection.
Test the oxygen sensor: Use a multimeter to measure the oxygen sensor voltage and confirm if it's consistently high, as indicated by the P0138 code.
Check for rich fuel condition: Inspect related components, such as the fuel injectors and fuel pressure regulator, for faults that may lead to a rich fuel mixture.

Repairing P0138

Repairs for the P0138 code typically include the following steps:

Replace the oxygen sensor: If the Bank 1, Sensor 2 oxygen sensor is faulty, replace it.
Repair or replace wiring: If any wiring or connectors are damaged, repair or replace them as needed to restore proper circuit function.
Fix fuel system issues: If a rich fuel condition is detected, address any faults with the fuel injectors, fuel pressure regulator or related components.
Clear the code and test: Use an OBD-II scanner to clear the code, then test the vehicle to ensure the issue is resolved and the code does not reappear.