AutoCodes – Cadillac – P0138 Cadillac

P0138 Cadillac 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 Cadillac 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 15,583

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

What does this mean?

What are the Possible Causes of the DTC P0138 Cadillac?

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 Cadillac?

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 Cadillac 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 Cadillac Code

1. What are common symptoms of OBDII code P0138 on a Cadillac?

- Common symptoms include poor fuel efficiency, rough idling, and the illumination of the check engine light.

2. What does the HO2S Circuit High Voltage Bank 1 Sensor 2 code mean for a Cadillac?

- This code indicates that the downstream oxygen sensor in Bank 1 is reading a voltage higher than normal, potentially indicating a problem with the sensor or the circuit.

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

- Possible causes include a faulty oxygen sensor, wiring issues, exhaust leaks, engine misfires, or a malfunctioning catalytic converter.

4. How can I diagnose the cause of the HO2S Circuit High Voltage Bank 1 Sensor 2 code in my Cadillac?

- Diagnosing this code usually involves checking the oxygen sensor wiring, testing the sensor's voltage output, and inspecting the exhaust system for leaks or damage.

5. Can I still drive my Cadillac with the P0138 trouble code?

- It is generally safe to drive your Cadillac with this code, but it is recommended to have it diagnosed and repaired as soon as possible to prevent further engine issues.

6. How can I repair the HO2S Circuit High Voltage Bank 1 Sensor 2 code in my Cadillac?

- Repair options may include replacing the oxygen sensor, repairing damaged wiring, fixing exhaust leaks, addressing engine misfires, or replacing the catalytic converter if necessary.

7. Will resetting the check engine light fix the P0138 code in a Cadillac?

- Simply resetting the check engine light will not fix the underlying issue causing the code. It is important to diagnose and repair the problem to prevent it from recurring.

8. How much does it typically cost to repair the P0138 code in a Cadillac?

- The cost of repairing this code can vary depending on the specific issue causing it. Costs may include parts such as a new oxygen sensor, labor, and diagnostic fees.

9. Are there any DIY tips for addressing the P0138 code in a Cadillac?

- DIY tips may include visually inspecting the oxygen sensor wiring, checking for exhaust leaks, and ensuring the engine is running smoothly to address potential causes of this code.

10. Can a P0138 code affect the emissions performance of a Cadillac?

- Yes, a P0138 code can affect the emissions performance of your Cadillac by potentially causing higher emissions levels and triggering the check engine light.