AutoCodes – Saturn – P0138 Saturn

P0138 Saturn Code - HO2S Circuit High Voltage Bank 1 Sensor 2

Quick Answer

The Heated Oxygen Sensors (HO2S) are used for fuel control and catalyst monitoring. Common causes include 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. Severity is Moderate - service should be scheduled soon. The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

What it means: P0138 Saturn indicates HO2S Circuit High Voltage Bank 1 Sensor 2.
Common causes: Common causes include 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.
Severity: Moderate - service should be scheduled soon.
Can I drive?: The vehicle may still be drivable for short trips if it runs normally, but avoid hard driving and repair it soon.

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Code Popularity 13,844

How popular is this code, among other codes? Low

Repair Importance Level

Moderate (Service soon) (2 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on May 26, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0138 Saturn Description

The Heated Oxygen Sensors (HO2S) are used for fuel control and catalyst monitoring. Each HO2S compares the oxygen content of the surrounding air with the oxygen content of the exhaust stream. When the engine is started, the Engine Control Module (ECM) operates in an Open Loop mode, ignoring the HO2S signal voltage while calculating the air-to-fuel ratio. While the engine runs, the HO2S heats up and begins to generate a voltage within a range of 0 - 1, 000 mV. Once sufficient HO2S voltage fluctuation is observed by the ECM, Closed Loop is entered. The ECM uses the HO2S voltage to determine the air-to-fuel ratio. An HO2S voltage that increases toward 1, 000 mV indicates a rich fuel mixture. An HO2S voltage that decreases toward 0 mV indicates a lean fuel mixture.
The heating elements inside each HO2S heat the sensor to bring the sensor up to operating conditions faster. This allows the system to enter Closed Loop earlier and the ECM to calculate the air-to-fuel ratio sooner.
The Diagnostic Trouble Code (DTC) will be set when the ECM detects that the HO2S voltage is greater than 1, 050 mV.

OBDII Code P0138 Saturn - HO2S Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com — P0138 Saturn Code - HO2S Circuit High Voltage Bank 1 Sensor 2

What does this mean?

What are the Possible Causes of the DTC P0138 Saturn?

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
Low or high fuel system pressure
Fuel contamination
Faulty fuel injectors
Exhaust gas leaks
Engine vacuum leaks

How to Fix the DTC P0138 Saturn?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What does this mean?

Code Tech Notes

Replacing the Rear Heated Oxygen Sensor (HO2S) Bank 1 usually takes care of the problem.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0138 Saturn code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

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About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P0138 Saturn Code

1. What are the common symptoms of OBDII code P0138 in a Saturn?

- Common symptoms include poor fuel economy, rough idling, engine hesitation, and an illuminated Check Engine light.

2. What does the OBDII code P0138 "HO2S Circuit High Voltage Bank 1 Sensor 2" mean for a Saturn?

- This code indicates that the oxygen sensor (O2 sensor) located downstream of the catalytic converter in Bank 1 is detecting a high voltage condition.

3. What are the possible causes of OBDII code P0138 in a Saturn?

- Possible causes include a faulty oxygen sensor, wiring issues in the sensor circuit, exhaust leaks, a malfunctioning catalytic converter, or an engine running too rich.

4. How serious is OBDII code P0138 in a Saturn?

- While the vehicle may still be drivable with this code, it can lead to decreased fuel efficiency and increased emissions. It is recommended to address this issue promptly to prevent further damage to the engine or catalytic converter.

5. Can I continue driving my Saturn with OBDII code P0138 present?

- It is generally safe to drive the vehicle with this code, but it is advisable to have it diagnosed and repaired as soon as possible to avoid potential engine performance issues.

6. How can I diagnose and repair OBDII code P0138 in my Saturn?

- Diagnosis typically involves testing the oxygen sensor, inspecting the sensor wiring, and checking for exhaust leaks. Repair may involve replacing the oxygen sensor, repairing wiring issues, or addressing other underlying causes.

7. Can a DIY enthusiast fix OBDII code P0138 in a Saturn?

- Depending on the individual's skill level and access to tools, some DIY enthusiasts may be able to address this code by replacing the oxygen sensor or fixing wiring issues. However, professional diagnosis and repair may be recommended for more complex issues.

8. Is it necessary to reset the OBDII code P0138 after making repairs in a Saturn?

- Yes, it is important to reset the code using an OBDII scanner after making any repairs to clear the Check Engine light and ensure that the issue has been resolved.

9. How much does it cost to repair OBDII code P0138 in a Saturn?

- The cost of repairing this code can vary depending on the specific cause of the issue, the labor rates in your area, and whether you choose to address the problem yourself or take it to a professional mechanic.

10. How can I prevent OBDII code P0138 from reoccurring in my Saturn?

- To prevent this code from reoccurring, it is important to address any underlying issues promptly, perform regular maintenance on your vehicle, and drive responsibly to minimize stress on the engine and emissions system.