AutoCodes – Scion – P0172 Scion

P0172 Scion Code - Fuel Trim System Too Rich Bank 1

Quick Answer

The fuel trim is related to the feedback compensation value, not to the basic injection duration. Common causes include Fuel injector leak or blockage, Faulty Mass Air Flow (MAF) sensor, Faulty Engine Coolant Temperature Sensor. 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: P0172 Scion indicates Fuel Trim System Too Rich Bank 1.
Common causes: Common causes include Fuel injector leak or blockage, Faulty Mass Air Flow (MAF) sensor, Faulty Engine Coolant Temperature Sensor.
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.

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Code Popularity 17,772

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Aug 24, 2022

Description
Step-by-Step Diagnostic Guide
Possible Causes
How To Fix
Cost to Diagnose
Comments
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Code P0172 Scion Description

The fuel trim is related to the feedback compensation value, not to the basic injection duration. The fuel trim consists of both short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the air-fuel ratio sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if lean.
Factors such as individual engine differences, wear over time, and changes in the operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.
Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the Engine Control Module (ECM) cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the fuel injection volumes estimated by the ECM also affect the average fuel trim learned value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learned value of the air fuel ratio). If the average fuel trim learned value exceeds the malfunction thresholds, the ECM interprets this as a fault in the fuel system and stores a Diagnostic Trouble Code (DTC).

OBDII Code P0172 Scion - Fuel Trim System Too Rich Bank 1 - AutoCodes.com — P0172 Scion Code - Fuel Trim System Too Rich Bank 1

What does this mean?

What are the Possible Causes of the DTC P0172 Scion?

Fuel injector leak or blockage
Faulty Mass Air Flow (MAF) sensor
Faulty Engine Coolant Temperature Sensor
Faulty Air Fuel Ratio (A/F) Sensor (Front Oxygen Sensor)
Incorrect fuel pressure
Gas leak from exhaust system
Air Fuel Ratio Sensor harness is open or shorted
Air Fuel Ratio Sensor circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P0172 Scion?

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 P0172 Scion 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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Need Help with the Code?

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Information for Specific Scion Models

P0172 2005 Scion xB — System Too Rich Bank 1
P0172 2006 Scion xB — System Too Rich Bank 1
P0172 2007 Scion xB — System Too Rich Bank 1

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.