AutoCodes – Mazda – P0155 Mazda

P0155 Mazda Code - HO2S21 Heater Circuit Fault

Quick Answer

Oxygen Sensors (O2S) or Heated Oxygen Sensors (HO2S) need to reach a minimum operating temperature of 750 degrees F to produce an accurate voltage signal. Common causes include Faulty Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1, Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit fuse, Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 harness is open shorted to ground. 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: P0155 Mazda indicates HO2S21 Heater Circuit Fault.
Common causes: Common causes include Faulty Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1, Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit fuse, Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 harness is open shorted to ground.
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 10,971

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 Mar 23, 2024

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Tech Notes
Cost to Diagnose
FAQs
Comments
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Code P0155 Mazda Description

Oxygen Sensors (O2S) or Heated Oxygen Sensors (HO2S) need to reach a minimum operating temperature of 750 degrees F to produce an accurate voltage signal. The faster the heated oxygen sensor reaches that temperature the faster the sensor will start sending an accurate signal to the Engine Control Module (ECM). In order to achieve the require temperature, a heater element is included inside the heated oxygen sensor. The ECM controls the heated oxygen sensor heater element based on signals from the engine coolant temperature and engine load. The ECM controls the heater element circuit by allowing current flow to ground. The ECM monitors the voltage signal received through the heater element circuit and determines the state of the circuit by comparing the voltage detected with the factory specifications.

OBDII Code P0155 Mazda - HO2S21 Heater Circuit Fault - AutoCodes.com — P0155 Mazda Code - HO2S21 Heater Circuit Fault

What does this mean?

What are the Possible Causes of the DTC P0155 Mazda?

Faulty Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1
Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit fuse
Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 harness is open shorted to ground
Heated Oxygen Sensor (H2OS) Bank 2 Sensor 1 circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0155 Mazda?

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

The code means that there is a problem with the heater element circuit of the heated oxygen sensor. The Engine Control Module (ECM) monitors how long it take the sensor to warm up and start sending an adequate signal. The code means the the sensor is taking too long to warm up. Replacing the Front Heated Oxygen Sensor (H2OS) Bank 2 usually takes care of the problem.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P0155 Mazda 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 P0155 Mazda Code

1. What does the P0155 code mean on a Mazda?

P0155 indicates a fault in the heater circuit of the oxygen sensor (HO2S) located in Bank 2, Sensor 1.

2. What are the common symptoms of a P0155 code in a Mazda?

Symptoms may include an illuminated check engine light, reduced fuel efficiency, poor engine performance, and higher emissions.

3. What causes the P0155 code in a Mazda?

Common causes include a faulty oxygen sensor, damaged wiring or connectors, a blown fuse, or an issue with the engine control module (ECM).

4. Which oxygen sensor does the P0155 code refer to?

The P0155 code refers to the upstream oxygen sensor (Sensor 1) on Bank 2, which monitors the air-fuel mixture before the catalytic converter.

5. Can I drive my Mazda with a P0155 code?

Driving with a P0155 code is possible but not recommended, as it can lead to poor fuel economy, increased emissions, and potential damage to the catalytic converter over time.

6. How do I fix the P0155 code on my Mazda?

Common fixes include replacing the faulty oxygen sensor, repairing damaged wiring, checking and replacing blown fuses, or addressing ECM issues.

7. How do I diagnose the P0155 code on a Mazda?

Diagnosis involves using an OBDII scanner, checking the oxygen sensor's resistance, inspecting wiring and connectors, and testing the heater circuit's voltage.

8. How much does it cost to fix the P0155 code on a Mazda?

Costs vary but typically range from $100 to $300 for parts and labor, depending on whether the oxygen sensor needs replacement or wiring repairs are required.

9. What tools are needed to repair the P0155 code on a Mazda?

Tools may include an OBDII scanner, a multimeter, a socket set, and possibly a specialized oxygen sensor socket.

10. Can a dirty oxygen sensor trigger the P0155 code?

A dirty sensor is unlikely to directly cause the P0155 code, as the code specifically relates to the heater circuit. However, a malfunctioning heater may be due to internal sensor damage.