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P1172 Acura Code - Air Fuel Ratio Sensor Circuit Out of Range High

Quick Answer

The P1172 code indicates that the rear air-fuel (A/F) sensor located in Bank 1 is reporting a voltage or signal that is higher than the expected range. Common causes include Faulty rear A/F sensor: The sensor itself may be malfunctioning, providing inaccurate readings to the ECM, Fuel injector issues: Leaking or stuck fuel injectors can cause excessive fuel delivery to the engine, Faulty fuel pressure regulator: If the regulator is not maintaining proper fuel pressure, it can lead to a rich mixture. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means
P1172 Acura indicates Air Fuel Ratio Sensor Circuit Out of Range High.
Common causes
Common causes include Faulty rear A/F sensor: The sensor itself may be malfunctioning, providing inaccurate readings to the ECM, Fuel injector issues: Leaking or stuck fuel injectors can cause excessive fuel delivery to the engine, Faulty fuel pressure regulator: If the regulator is not maintaining proper fuel pressure, it can lead to a rich mixture.
Severity
High - diagnose this code as soon as possible.
Can I drive?
Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.
What is this?
Table of contents Created and updated by William Orellana on Sep 02, 2025
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Code P1172 Acura Description

The P1172 code indicates that the rear air-fuel (A/F) sensor located in Bank 1 is reporting a voltage or signal that is higher than the expected range. The air-fuel sensor, also known as a wideband O2 sensor, plays a critical role in the vehicle's emissions control system by measuring the oxygen content in the exhaust gases. This information is vital for the engine control module (ECM) to adjust the air-fuel mixture for optimal combustion. When the sensor's output is too high, it suggests that the engine is running rich (too much fuel compared to air), which can lead to various performance issues.
OBDII Code P1172 Acura - Air Fuel Ratio Sensor Circuit Out of Range High
P1172 Acura Code - Air Fuel Ratio Sensor Circuit Out of Range High

Common Causes of P1172 Acura

  1. Faulty rear A/F sensor: The sensor itself may be malfunctioning, providing inaccurate readings to the ECM.
  2. Fuel injector issues: Leaking or stuck fuel injectors can cause excessive fuel delivery to the engine.
  3. Faulty fuel pressure regulator: If the regulator is not maintaining proper fuel pressure, it can lead to a rich mixture.
  4. Exhaust leaks: Leaks in the exhaust system can affect the sensor's readings, leading to erroneous signals.
  5. Wiring or connector issues: Damaged wiring or poor connections to the A/F sensor can result in high voltage readings.

Symptoms of P1172 Acura

  1. Decreased fuel economy: The vehicle may consume more fuel than usual due to an overly rich mixture.
  2. Rough idling: The engine may exhibit unstable idling or stalling due to improper air-fuel ratios.
  3. Check Engine Light (CEL): The illumination of the CEL on the dashboard is a common indicator of this code.
  4. Increased emissions: The vehicle may fail emissions tests due to higher levels of harmful pollutants.
  5. Poor acceleration: Drivers may notice a lack of power or sluggishness during acceleration.

How to Fix P1172 Acura

  1. Diagnostic Testing: Begin with a thorough diagnostic scan to confirm the P1172 code and check for any related codes that may provide additional context.
  2. Visual Inspection: Inspect the wiring and connectors associated with the rear A/F sensor for damage, corrosion, or loose connections.
  3. Sensor Replacement: If the sensor is determined to be faulty, replace it with a new, OEM-quality part to ensure accurate readings.
  4. Check Fuel System: Test the fuel pressure and inspect the fuel injectors for proper operation to rule out fuel delivery issues.
  5. Clear Codes and Test Drive: After repairs, clear the diagnostic codes and take the vehicle for a test drive to ensure the issue has been resolved and monitor for any reoccurrence of the P1172 code.

Cost to Fix P1172 Acura

The typical repair costs for addressing a P1172 code can range from $150 to $600, depending on the specific cause of the issue. This estimate includes parts such as a new A/F sensor (which can cost between $100 and $300) and labor costs, which can vary widely based on location and shop rates. Labor rates typically range from $80 to $150 per hour, with metropolitan areas or dealerships often charging more, while independent shops may offer lower rates. It is advisable to check local rates for a more precise estimate and to consider that diagnostic time may also be required before any repairs are made.

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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 P1172 Acura Code

1. What are common symptoms of OBDII code P1172 in an Acura related to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Common symptoms may include poor engine performance, decreased fuel efficiency, and illuminated Check Engine light.

2. What are the possible causes of OBDII code P1172 in an Acura indicating an issue with the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Possible causes include a faulty rear air fuel ratio sensor, damaged wiring or connectors, exhaust leaks, or issues with the engine's air-fuel mixture.

3. How can I diagnose the OBDII code P1172 on my Acura if it relates to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Diagnosing this code may involve using an OBDII scanner to retrieve the fault code, visually inspecting the sensor and its connections, and performing voltage tests to check sensor operation.

4. Can I continue driving my Acura with OBDII code P1172 indicating an issue with the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- It is not recommended to continue driving with this code present, as it can lead to further engine problems and potential damage if left unresolved.

5. How can I repair OBDII code P1172 in my Acura related to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Repair options may include replacing the rear air fuel ratio sensor, repairing damaged wiring or connectors, fixing exhaust leaks, and ensuring the engine's air-fuel mixture is correct.

6. Is it possible to reset the OBDII code P1172 in an Acura myself if it pertains to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- You can attempt to clear the code using an OBDII scanner, but it is important to address the underlying issue causing the fault code to prevent it from reappearing.

7. How much does it typically cost to repair OBDII code P1172 in an Acura involving the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Repair costs can vary depending on the exact cause of the issue, but it may involve sensor replacement, wiring repairs, or other necessary fixes that could range from a few hundred to over a thousand dollars.

8. Are there any DIY tips for resolving OBDII code P1172 in an Acura associated with the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- DIY tips may include carefully inspecting sensor connections and wiring for damage, ensuring proper installation of a new sensor if needed, and following manufacturer guidelines for troubleshooting the code.

9. How urgent is it to address OBDII code P1172 in an Acura linked to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- It is recommended to address this code promptly to prevent any potential engine damage or performance issues, as prolonged driving with this fault can lead to more significant problems.

10. Can weather conditions or driving habits affect the occurrence of OBDII code P1172 in an Acura related to the Rear A/F Sensor Bank 1 Sensor 1 Circuit Out Of Range High?

- Extreme weather conditions or driving habits that put stress on the engine can potentially impact the occurrence of this code, but the root cause is typically related to sensor or wiring issues that need attention.

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