P0173 Fuel Trim too Rich (Bank 1)


P0173 Fuel Trim too Rich (Bank 1) is a common diagnostic trouble code (DTC) that indicates an issue with the fuel trim on your vehicle’s bank 1. In this article, we will discuss the meaning of fuel trim, the causes of the P0173 code, how to diagnose it, and the possible solutions to fix it. Additionally, we will explore ways to prevent the code from appearing in the future. So, let’s dive in!

What is Fuel Trim?

Fuel trim refers to the adjustments made by your vehicle’s engine control module (ECM) to maintain the optimal air-fuel ratio. It is crucial for achieving maximum efficiency, minimizing emissions, and ensuring proper engine performance. The fuel trim is divided into two types: short-term fuel trim (STFT) and long-term fuel trim (LTFT).

Understanding Fuel Trim Numbers

STFT measures the immediate changes in the air-fuel mixture, while LTFT is the average of the STFT adjustments over time. Positive fuel trim numbers indicate a lean condition (too much air, not enough fuel), while negative numbers indicate a rich condition (too much fuel, not enough air). The P0173 code is triggered when the fuel trim is too rich on bank 1, meaning there is an excess of fuel compared to air in the mixture.

Causes of P0173 Code

There are several potential causes of the P0173 code. Here are the most common ones:

Vacuum Leaks

Vacuum leaks can cause unmetered air to enter the engine, leading to an incorrect air-fuel mixture. The ECM will compensate for the lean condition by increasing the amount of fuel, which can trigger the P0173 code.

Faulty Oxygen Sensors

Oxygen sensors monitor the exhaust gases and send signals to the ECM, which then adjusts the fuel trim. A faulty oxygen sensor can send incorrect signals, causing the ECM to add too much fuel to the mixture.

Fuel Pressure Issues

If the fuel pressure is too high, it can cause the injectors to deliver more fuel than needed. This can lead to a rich condition and trigger the P0173 code.

Dirty Mass Air Flow Sensor

The mass air flow (MAF) sensor measures the amount of air entering the engine. A dirty or malfunctioning MAF sensor can provide incorrect readings, causing the ECM to add excessive fuel.

Malfunctioning Fuel Injectors

Fuel injectors can become clogged or stuck open, causing them to deliver too much fuel to the engine. This results in a rich condition and can trigger the P0173 code.

Diagnosing P0173 Code

Detecting and diagnosing the P0173 code requires a systematic approach. Here’s how you can proceed:

Preliminary Checks

Begin by inspecting the obvious. Check for vacuum leaks, loose connections, damaged wiring, and other visible issues. Also, examine the condition of the oxygen sensors and the MAF sensor.

Diagnostic Procedures

If the preliminary checks don’t reveal the issue, more in-depth diagnostics will be necessary. You may need to use an OBD-II scanner to read the fault codes, a fuel pressure gauge to measure fuel pressure, and a multimeter to test the oxygen sensors and MAF sensor.

Repairing P0173 Code

The repair process will depend on the specific cause of the P0173 code.

Common Fixes

Common fixes for the P0173 code include repairing vacuum leaks, replacing faulty oxygen sensors, adjusting fuel pressure, cleaning or replacing the MAF sensor, and servicing or replacing malfunctioning fuel injectors.

Preventing P0173 Code

Prevention is better than cure. Regular maintenance of your vehicle can help prevent the P0173 code from triggering. This includes regular checks and cleaning of sensors, timely replacement of faulty parts, and ensuring the fuel system remains clean and efficient.


The P0173 Fuel Trim too Rich (Bank 1) code can be a bit complex to diagnose and fix due to the number of potential causes. However, understanding what the code means, its common causes, and how to diagnose and fix it can help you deal with it effectively. Regular vehicle maintenance can also help prevent this and other codes from appearing. Remember, when in doubt, always consult with a professional mechanic.


1. What does the P0173 code mean?

The P0173 code means that the fuel trim on your vehicle’s bank 1 is too rich, indicating an excess of fuel compared to air in the air-fuel mixture.

2. What are the common causes of the P0173 code?

Common causes include vacuum leaks, faulty oxygen sensors, high fuel pressure, a dirty MAF sensor, and malfunctioning fuel injectors.

3. How do I diagnose the P0173 code?

Diagnosing the P0173 code involves a combination of visual inspections, preliminary checks, and more in-depth diagnostics using tools like an OBD-II scanner, fuel pressure gauge, and a multimeter.

4. How can I fix the P0173 code?

Fixing the P0173 code depends on its cause. It could involve repairing vacuum leaks, replacing faulty sensors, adjusting fuel pressure, or servicing fuel injectors.

5. How can I prevent the P0173 code?

Regular vehicle maintenance, including regular checks and cleaning of sensors, timely replacement of faulty parts, and ensuring the fuel system remains clean and efficient, can help prevent the P0173 code.