P1157 Lack Of HO2S21 Switch – Sensor Indicates Rich

As a car expert, I understand how frustrating it can be to encounter issues with your vehicle. One common problem that many car owners face is the P1157 error code, which indicates a lack of HO2S21 switch and sensor indicating rich. In this article, I will provide you with a step-by-step guide on how to fix this issue and get your car running smoothly again.

What is P1157 Lack Of HO2S21 Switch – Sensor Indicates Rich?

Before we dive into the solution, let’s first understand what the P1157 error code means. This code is related to the oxygen sensor in your car’s exhaust system. The HO2S21 sensor is responsible for monitoring the oxygen levels in the exhaust gases and sending this information to the engine control module (ECM). If the sensor detects a rich air-fuel mixture, it will trigger the P1157 error code.

Step-by-Step Guide to Fix P1157 Lack Of HO2S21 Switch – Sensor Indicates Rich

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1. Check the Oxygen Sensor

The first step in fixing the P1157 error code is to check the oxygen sensor. You can do this by using an OBD-II scanner to read the error code and determine which sensor is causing the issue. Once you have identified the sensor, you can use a multimeter to test its voltage output. If the voltage is outside the normal range, you may need to replace the sensor.

2. Check the Wiring

If the oxygen sensor is functioning properly, the next step is to check the wiring. Look for any signs of damage or corrosion on the wires and connectors. You can use a multimeter to test the continuity of the wires and ensure that they are properly connected.

3. Check the Fuel System

If the wiring is not the issue, the problem may be with the fuel system. Check the fuel pressure and ensure that the fuel injectors are functioning properly. You can use a fuel pressure gauge to test the pressure and a noid light to check the injectors.

4. Check the Air Intake System

Another possible cause of the P1157 error code is a problem with the air intake system. Check the air filter and ensure that it is clean and free of debris. You can also check the air intake hose for any signs of damage or leaks.

5. Check the Exhaust System

Finally, check the exhaust system for any leaks or damage. A leak in the exhaust system can cause the oxygen sensor to detect a rich air-fuel mixture and trigger the P1157 error code. You can use a smoke machine to test for leaks in the exhaust system.


Fixing the P1157 error code may seem daunting, but with the right tools and knowledge, it can be done. By following the step-by-step guide outlined in this article, you can identify and fix the issue with your car’s oxygen sensor and get back on the road in no time.


1. Can I drive my car with the P1157 error code?

It is not recommended to drive your car with the P1157 error code as it can cause damage to your engine and reduce fuel efficiency.

2. How much does it cost to fix the P1157 error code?

The cost of fixing the P1157 error code can vary depending on the cause of the issue. It can range from a simple sensor replacement to a more complex fuel system repair.

3. How often should I replace my oxygen sensor?

It is recommended to replace your oxygen sensor every 60,000 to 90,000 miles to ensure optimal performance and fuel efficiency.