AutoCodes – Toyota – P0138 2008 Toyota Prius

P0138 2008 Toyota Prius 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 2008 Toyota Prius 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 7,610

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 Jul 04, 2020

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P0138 2008 Toyota Prius 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 2008 Toyota Prius - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2 - AutoCodes.com — P0138 2008 Toyota Prius Code - Oxygen Sensor Circuit High Voltage Bank 1 Sensor 2

What does this mean?

What are the Possible Causes of the DTC P0138 2008 Toyota Prius?

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 2008 Toyota Prius?

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 is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0138 2008 Toyota Prius 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 2008 Toyota Prius 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 2008 Toyota Prius Code

1. What does the OBDII code P0138 mean for a 2008 Toyota Prius?

The code P0138 indicates a high voltage condition in the oxygen sensor circuit of Bank 1 Sensor 2 in a 2008 Toyota Prius.

2. What are common symptoms of a P0138 code in a 2008 Toyota Prius?

Common symptoms of a P0138 code include poor fuel economy, rough idling, engine misfires, and the illumination of the check engine light.

3. What are possible causes of the P0138 code in a 2008 Toyota Prius?

Potential causes of a P0138 code in a 2008 Toyota Prius include a faulty oxygen sensor, wiring issues in the oxygen sensor circuit, or an engine running too rich.

4. How can I diagnose a P0138 code in my 2008 Toyota Prius?

Diagnosing a P0138 code involves using an OBDII scanner to retrieve the code, checking the oxygen sensor's voltage readings, inspecting the sensor's wiring for damage, and testing the sensor's heater circuit.

5. Can a P0138 code on a 2008 Toyota Prius be fixed at home?

Depending on the underlying cause, fixing a P0138 code at home may be possible by replacing the oxygen sensor, repairing damaged wiring, or addressing issues related to the engine's air-fuel mixture.

6. Is it safe to continue driving a 2008 Toyota Prius with a P0138 code?

While it may be safe to drive a Prius with a P0138 code for a short period, it is recommended to address the issue promptly to prevent potential damage to the catalytic converter and ensure optimal engine performance.

7. How much does it typically cost to repair a P0138 code on a 2008 Toyota Prius?

The cost of repairing a P0138 code in a 2008 Toyota Prius can vary depending on the specific issue, but it may range from $100 to $300 for parts and labor.

8. Can a P0138 code be triggered by other underlying issues in a 2008 Toyota Prius?

Yes, a P0138 code can sometimes be triggered by issues such as a vacuum leak, exhaust system leaks, or problems with the fuel delivery system in a 2008 Toyota Prius.

9. Will resetting the check engine light clear a P0138 code in a 2008 Toyota Prius?

Resetting the check engine light may temporarily clear the P0138 code, but if the underlying issue is not addressed, the code is likely to reappear after driving the vehicle for some time.

10. How important is it to address a P0138 code promptly in a 2008 Toyota Prius?

It is crucial to address a P0138 code promptly in a 2008 Toyota Prius to prevent potential damage to the engine, emissions system, and catalytic converter, as well as to ensure optimal fuel efficiency and performance.