AutoCodes – Toyota – P0138 2005 Toyota Highlander

P0138 2005 Toyota Highlander Code - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2

Quick Answer

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. 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 2005 Toyota Highlander indicates Oxygen Sensor 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 6,755

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 Jun 14, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0138 2005 Toyota Highlander 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 2005 Toyota Highlander - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com — P0138 2005 Toyota Highlander Code - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2

What does this mean?

What are the Possible Causes of the DTC P0138 2005 Toyota Highlander?

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

How to Fix the DTC P0138 2005 Toyota Highlander?

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 Bank 1 usually takes care of the problem.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0138 2005 Toyota Highlander 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.

Need more information about the P0138 2005 Toyota Highlander code?

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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 2005 Toyota Highlander Code

1. What are the common symptoms of OBDII code P0138 on a 2005 Toyota Highlander?

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

2. What does the OBDII code P0138 "Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2" mean?

- This code indicates that the oxygen sensor downstream of the catalytic converter in bank 1 is reading a higher voltage than normal.

3. What are the possible causes of OBDII code P0138 in a 2005 Toyota Highlander?

- Possible causes include a faulty oxygen sensor, wiring issues, a vacuum leak, exhaust leaks, or a problem with the catalytic converter.

4. How can I diagnose the source of OBDII code P0138 on my 2005 Toyota Highlander?

- Diagnose by visually inspecting the oxygen sensor and its wiring, checking for exhaust leaks, performing voltage tests, and using a scan tool to monitor sensor readings.

5. What are the consequences of ignoring OBDII code P0138 in a 2005 Toyota Highlander?

- Ignoring this code can lead to decreased fuel efficiency, engine performance issues, and potential damage to the catalytic converter over time.

6. How can I repair OBDII code P0138 on a 2005 Toyota Highlander?

- Repair options include replacing the oxygen sensor, repairing or replacing damaged wiring, fixing exhaust leaks, and addressing any underlying issues causing the high voltage reading.

7. Can I continue to drive my 2005 Toyota Highlander with OBDII code P0138?

- It is not recommended to drive the vehicle for an extended period with this code present, as it can lead to further damage and decreased performance.

8. Will resetting the check engine light make OBDII code P0138 disappear?

- Resetting the check engine light may temporarily turn it off, but the underlying issue causing code P0138 will still need to be diagnosed and repaired.

9. How much does it typically cost to fix OBDII code P0138 on a 2005 Toyota Highlander?

- The cost of repairs can vary depending on the exact cause of the code, but it may range from $100 to $300 for parts and labor.

10. Is it possible to prevent OBDII code P0138 from recurring in the future?

- Regular maintenance, such as changing the oxygen sensor at recommended intervals, inspecting the exhaust system, and addressing any engine issues promptly, can help prevent the recurrence of this code.