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P0138 - O2 Sensor Circuit High Voltage Bank 1 Sensor 2

Possible causes
- Faulty Rear Heated Oxygen Sensor Bank 1
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Intake air leaks
- Exhaust gas leaks
- Inappropriate fuel pressure
- Faulty fuel injectors
What does this mean? What does this mean?
Tech notes
Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem.
What does this mean? What does this mean?
When is the code detected?
The P0138 code is set when the Engine Control Module (ECM) detects that the rear O2 sensor signal voltage remains excessively high for an extended period of time.
Possible symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- High Fuel Consumption
- Excessive Smoke from Exhaust
P0138 Description

The Heated Oxygen Sensor 2 (HO2S) (Rear O2 Sensor), after three way catalyst (manifold), monitors the oxygen level in the exhaust gas on each bank. For optimum catalyst operation, the air fuel mixture (air-fuel ratio) must be maintained near the ideal stoichiometric ratio. The HO2S output voltage changes suddenly in the vicinity of the stoichiometric ratio. The Engine Control Module (ECM) adjusts the fuel injection time so that the air-fuel ratio is nearly stoichiometric. The HO2S generates a voltage between 0.1 and 0.9 V in response to oxygen in the exhaust gas. If the oxygen in the exhaust gas increases, the air-fuel ratio becomes Lean. The ECM interprets Lean when the HO2S voltage is below 0.45 V. If the oxygen in the exhaust gas decreases, the air-fuel ratio becomes Rich. The ECM interprets Rich when the HO2S voltage is above 0.45 V.

OBDII Code P0138 - O2 Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com
P0138 Information for specific makes
P0138 ACURA HO2S Bank 1 Sensor 2 Circuit Low Voltage  P0138 Image
P0138 AUDI HO2S12 Sensor Circuit High Voltage  P0138 Image
P0138 BMW O2 Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 BUICK HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 CADILLAC HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 CHEVROLET HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 CHRYSLER O2 sensor 1/2 Circuit high  P0138 Image
P0138 DODGE O2 sensor 1/2 Circuit high  P0138 Image
P0138 FORD O2 Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 GMC HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 HONDA HO2S Bank 1 Sensor 2 Circuit Low Voltage  P0138 Image
P0138 HYUNDAI HO2S Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 INFINITI HO2S12 Circuit High Voltage  P0138 Image
P0138 ISUZU HO2S Circuit Low Voltage Sensor 2  P0138 Image
P0138 JAGUAR O2 Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 JEEP O2 sensor 1/2 Circuit high  P0138 Image
P0138 KIA HO2S12 Circuit High Voltage  P0138 Image
P0138 LEXUS Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 MAZDA HO2S RR Circuit High Input  P0138 Image
P0138 MERCEDES-BENZ O2 Sensor Circuit High Voltage Bank 1 Sensor 2
P0138 MITSUBISHI Cylinder 1-4 Heated Oxygen Rear Sensor Circuit High Voltage  P0138 Image
P0138 NISSAN HO2S12 Circuit High Voltage  P0138 Image
P0138 PONTIAC HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 SATURN HO2S Circuit High Voltage Bank 1 Sensor 2
P0138 SCION Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 SUBARU HO2S12 Circuit High Voltage  P0138 Image
P0138 TOYOTA Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2  P0138 Image
P0138 VOLKSWAGEN HO2S12 Sensor Circuit High Voltage  P0138 Image
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