P0172 Subaru Code - System Too Rich Bank 1
Quick Answer
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. Common causes include Faulty Front Heated Oxygen Sensor, Faulty Spark Plugs, Faulty Mass Air Flow (MAF) 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 Subaru indicates System Too Rich Bank 1.
- Common causes
- Common causes include Faulty Front Heated Oxygen Sensor, Faulty Spark Plugs, Faulty Mass Air Flow (MAF) 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.
Code P0172 Subaru Description
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).
What are the Possible Causes of the DTC P0172 Subaru?
- Faulty Front Heated Oxygen Sensor
- Faulty Spark Plugs
- Faulty Mass Air Flow (MAF) sensor
- Exhaust Gas Leaks
- Ignition Misfiring
- Incorrect Fuel Pressure
- Faulty Fuel Injectors
How to Fix the DTC P0172 Subaru?
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 Subaru 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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Frequently Asked Questions about P0172 Subaru Code
1. What does the OBDII code P0172 mean on a Subaru?
P0172 indicates that the engine control module (ECM) has detected the air-fuel mixture is too rich on Bank 1, meaning there is too much fuel or not enough air.
2. What are the common symptoms of code P0172 on a Subaru?
Symptoms may include poor fuel economy, black smoke from the exhaust, rough idling, hesitation during acceleration, or a strong fuel smell.
3. What causes the P0172 code on a Subaru?
Common causes include a dirty or faulty mass airflow sensor (MAF), a leaking fuel injector, a clogged air filter, a malfunctioning oxygen sensor, or excessive fuel pressure.
4. Can a dirty air filter cause a P0172 code on a Subaru?
Yes, a clogged or dirty air filter can restrict airflow to the engine, causing the air-fuel mixture to become too rich and triggering the P0172 code.
5. How do I diagnose the P0172 code on my Subaru?
Start by checking the air filter, inspecting the mass airflow sensor, and verifying the fuel pressure. Use a scan tool to monitor oxygen sensor readings and fuel trim data for abnormalities.
6. Can a faulty mass airflow sensor cause the P0172 code on a Subaru?
Yes, a malfunctioning mass airflow sensor can send incorrect data to the ECM, leading to an overly rich fuel mixture and triggering the P0172 code.
7. Is it safe to drive with the P0172 code on my Subaru?
Driving with a P0172 code is not recommended, as it can lead to poor fuel economy, increased emissions, and potential damage to the catalytic converter.
8. How can I fix the P0172 code on my Subaru?
Possible fixes include cleaning or replacing the mass airflow sensor, replacing a faulty oxygen sensor, repairing fuel injector leaks, or replacing a clogged air filter.
9. Can a vacuum leak cause the P0172 code on a Subaru?
While vacuum leaks typically cause a lean condition (P0171), a rare scenario with certain vacuum issues could potentially contribute to a rich condition.
10. How much does it cost to fix the P0172 code on a Subaru?
The repair cost depends on the root cause. For example, replacing an air filter might cost $20–$50, while a new mass airflow sensor or oxygen sensor could cost $150–$300 or more, including labor.
Discuss the causes and fixes for P0172 Subaru OBDII Code
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I was getting P0171 error code. Then had an exhaust psi test and the meter pegged past 30. So I replaced the expensive cataleptic converter. $650 installed (this one is funky shaped so they mark it up big time). I drove it on the highway for around 80 miles now Im getting error code P0172. The exhaust guy said there is another cat. converter but that can be replaced with a universal $250 installed.
It does run better but it still jumps during acceleration a little bit. So 02 sensor or the other cat. converter is the direction im leaning.. thoughts please. -
O2 sensor is the most likely cause, but make sure there are no intake or exhaust leaks first. Leaks could trigger the P0171 code.
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Got the P0172 code on my '09 Impreza, I'm having issues with idle dropping to about 500 and coming back up to 900. Only does it while car is in neutral. 5 spd manual transmission. Plugs have been replaced and throttle body and fuel injectors cleaned.
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Check Mass Air Flow (MAF) sensor and if possible change the air filter. Sometimes derbies get pass the air filter and get stuck on the air filter. Also, make sure there are no intake leaks (loose or damage hoses)
Click here to enlarge image -
Have a 2009 Sti, dropped a P0172 the other day, A/F ratio started jumping between 10.5-16.8 (Usually sits solid at 14.7).
Replaced both the up and downstream O2 sensor, fuel filter, MAF sensor was cleaned.
All fluids are staying level, has the very obvious smell of running rich when started.
Seems to be at its worse during enrichment, after enrichment it stays between 12.5-15 A/F.Continues to have a jumpy A/F ratio and idle but the code has cleared.
Not sure why the code cleared or what the issue is at this point -
after i changed the spark plugs, this problem happened. Are there somethings wrong with the plug? I am not too sure, plz help~
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i had the same issue with my 2008 subaru impreza wrx sti hatchback. it was solve with no issues. my issuse was the connector to the MAF wires was broken so got it and mended it. ECU was reading maf properly so the code pop up.
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