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Rock Sam

Rock Sam 8/15/2018

2008 Hummer H3 Base 5 Cyl 3.70L

Preventive Maintenance

What are the causes of O2 Sensor Circuit High Voltage (Bank 1)? How to fix the Error Code P0138?

1 Answer

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What the P0138 code means?

P0138 is the OBD-II generic code indicating the O2 sensor for bank 1 sensor 2 fails to have a lower voltage output below 1.2 volts for more than 10 seconds indicating a lack of oxygen in the exhaust stream.

What causes the P0138 code?

Faulty O2 sensor

Short to battery voltage in O2 sensor signal circuit

High fuel pressure

What are the symptoms of the P0138 code?

These could include a lean or rich condition in the engine, decreased fuel efficiency, black smoke from the
tailpipe, and an illuminated service engine soon lamp.

Common mistakes when diagnosing the P0138 code:

Technicians report replacement of oxygen sensors, when lean or rich engine conditions are the cause of
incorrect readings, is fairly common. Replacement of the incorrect oxygen sensor is also a possibility.

What repairs can fix the P0138 code?

Replacing the O2 sensor for bank 1 sensor 2

Repairing or replacing the wiring or connection to the O2 sensor for bank 1 sensor 2

Replacing the catalyst in front of the sensor

Repairing a leaking injector


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