AutoCodes – Toyota – P0138 2004 Toyota Highlander

P0138 2004 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 2004 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 4,931

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 2004 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 2004 Toyota Highlander - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com — P0138 2004 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 2004 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 2004 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 2004 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 2004 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 2004 Toyota Highlander Code

1. What does OBDII code P0138 for a 2004 Toyota Highlander mean?

The code P0138 indicates a high voltage condition in the oxygen sensor circuit of Bank 1 Sensor 2 in a 2004 Toyota Highlander.

2. What are the common symptoms of OBDII code P0138 on a 2004 Toyota Highlander?

Common symptoms of P0138 may include poor fuel efficiency, rough idling, hesitation during acceleration, and the illumination of the check engine light.

3. What are the possible causes of OBDII code P0138 on a 2004 Toyota Highlander?

Some common causes of code P0138 on a 2004 Toyota Highlander include a faulty oxygen sensor, wiring issues, exhaust leaks, or a problem with the engine's computer system.

4. How can I diagnose the OBDII code P0138 on my 2004 Toyota Highlander?

To diagnose code P0138, you can use an OBDII scanner to retrieve the specific fault code. Additionally, you can visually inspect the wiring and connections related to Bank 1 Sensor 2 and perform voltage tests on the oxygen sensor.

5. Can I drive my 2004 Toyota Highlander with OBDII code P0138?

It is generally not recommended to drive your vehicle with an unresolved P0138 code, as it can lead to poor engine performance and potential damage to other components.

6. How can I repair OBDII code P0138 on my 2004 Toyota Highlander?

Repairing P0138 may involve replacing the Bank 1 Sensor 2 oxygen sensor, repairing any wiring issues, fixing exhaust leaks, or resetting the engine's computer system.

7. Can I reset the check engine light after fixing OBDII code P0138 on my 2004 Toyota Highlander?

Yes, once you have resolved the issue causing code P0138, you can use an OBDII scanner to clear the code and reset the check engine light on your 2004 Toyota Highlander.

8. How much does it cost to repair OBDII code P0138 on a 2004 Toyota Highlander?

The cost of repairing P0138 can vary depending on the specific issue causing the code. Replacing the oxygen sensor or fixing wiring problems may range from $100 to $300 or more, including parts and labor.

9. How often does OBDII code P0138 occur in a 2004 Toyota Highlander?

The occurrence of code P0138 in a 2004 Toyota Highlander can vary depending on factors such as vehicle age, mileage, and maintenance history. It is relatively common in vehicles with aging oxygen sensors.

10. Can I prevent OBDII code P0138 from appearing in my 2004 Toyota Highlander?

Regular maintenance, such as replacing oxygen sensors at recommended intervals and addressing any engine issues promptly, can help prevent the recurrence of code P0138 in a 2004 Toyota Highlander.