P0171 Subaru Code - System Too Lean Bank 1
Quick Answer
When the OBD-II system detects that the air-fuel mixture in the engine is too lean on Bank 1 (cylinder bank that contains cylinder #1), it triggers the P0171 code. Common causes include Vacuum leaks in the intake system, Faulty oxygen sensor, Dirty or clogged fuel injectors. 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
- P0171 Subaru indicates System Too Lean Bank 1.
- Common causes
- Common causes include Vacuum leaks in the intake system, Faulty oxygen sensor, Dirty or clogged fuel injectors.
- 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 P0171 Subaru Description
When the OBD-II system detects that the air-fuel mixture in the engine is too lean on Bank 1 (cylinder bank that contains cylinder #1), it triggers the P0171 code. This means that there is an imbalance in the air-fuel ratio, with more air than fuel entering the combustion chamber. This can lead to poor engine performance, reduced fuel efficiency, and potential damage to the engine over time. The underlying cause of this issue could be related to a vacuum leak, faulty oxygen sensor, fuel system issues, or a problem with the mass airflow sensor.
Common Causes of P0171 Subaru
- Vacuum leaks in the intake system
- Faulty oxygen sensor
- Dirty or clogged fuel injectors
- Issues with the mass airflow sensor
- Fuel pump problems
Symptoms of P0171 Subaru
- Rough idling
- Engine hesitation or stumbling
- Decreased fuel efficiency
- Engine misfires
- Check Engine Light illuminated
How to Fix P0171 Subaru
- Check for vacuum leaks and repair or replace any damaged hoses or gaskets.
- Test and replace the oxygen sensor if faulty.
- Clean or replace clogged fuel injectors.
- Inspect and clean the mass airflow sensor or replace if necessary.
- Check fuel pump operation and replace if needed.
Cost to Fix P0171 Subaru
The cost for repairing a P0171 code can vary depending on the specific cause of the issue. On average, the cost could range from $100 to $500, including parts and labor. However, it's important to note that labor rates and part prices can vary significantly, so it's recommended to get a detailed estimate from a trusted auto repair shop.
Tech Notes for P0171 Subaru
When is the Code Detected?
- The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)
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Frequently Asked Questions about P0171 Subaru Code
1. What are the common symptoms of OBDII code P0171 (System Too Lean Bank 1) on a Subaru?
The common symptoms of code P0171 in a Subaru include rough idling, poor acceleration, increased fuel consumption, and a possible Check Engine Light.
2. What are the possible causes of OBDII code P0171 in a Subaru?
Common causes of code P0171 in a Subaru include a vacuum leak, faulty oxygen sensor, dirty or clogged fuel injectors, a malfunctioning mass airflow sensor, or a fuel delivery issue.
3. How can I diagnose a vacuum leak causing OBDII code P0171 in my Subaru?
To diagnose a vacuum leak, you can visually inspect hoses and connections for any cracks or damage, use a smoke machine to detect leaks, or spray a flammable substance around suspected areas while the engine is running to listen for changes in RPM.
4. What are some repair tips for fixing OBDII code P0171 in a Subaru?
Repair tips for code P0171 in a Subaru include fixing any vacuum leaks, cleaning or replacing the oxygen sensor, cleaning the mass airflow sensor, checking and cleaning the fuel injectors, and ensuring the fuel pressure is within specifications.
5. Can a dirty air filter trigger OBDII code P0171 in a Subaru?
Yes, a dirty air filter can restrict airflow into the engine, causing a lean fuel mixture and triggering code P0171. Regularly changing the air filter is a simple maintenance task that can help prevent this issue.
6. Is it safe to continue driving my Subaru with OBDII code P0171 active?
While it may be safe to drive with code P0171 in the short term, it is recommended to address the issue promptly to prevent potential damage to the engine or emissions system in the long run.
7. How can I reset the Check Engine Light after repairing OBDII code P0171 in my Subaru?
You can reset the Check Engine Light using an OBDII scanner or by disconnecting the car battery for a few minutes. However, it is important to ensure the underlying issue causing code P0171 has been properly addressed.
8. Will OBDII code P0171 affect the overall performance of my Subaru?
Yes, code P0171 can affect the overall performance of your Subaru by causing issues such as poor fuel efficiency, reduced power, rough idling, and potential engine damage if left unresolved.
9. Can a misfiring spark plug lead to OBDII code P0171 in a Subaru?
Yes, a misfiring spark plug can affect the air-fuel mixture in the engine, leading to a lean condition and triggering code P0171. It is important to maintain and replace spark plugs as part of routine maintenance.
10. How often should I have my Subaru's fuel system components inspected to prevent OBDII code P0171?
It is recommended to have your Subaru's fuel system components, such as fuel injectors, fuel filter, and fuel pressure regulator, inspected during regular maintenance intervals to prevent issues like code P0171.
Discuss the causes and fixes for P0171 Subaru OBDII Code
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Was getting this code at about once per tank full of gas. Also got "cat efficiency low" low. Turned out to be onset of Mass Airflow Sensor failure. Had irregular idle and stalling problems too. Then the MAF failed completely one rainy night on I-84 in NY State. Finally got the OBD2 code "MAF low output" that told me what the problem had been. $240 for a rebuilt MAF from Autozone and all the problems have gone away. Except one. Get an "EGR flow low" OBD2 code about once every tank of gas. Have cleaned the valve ports; cylinder head tapping and pipe. Checked for vacuum leaks; no joy.
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Subaru Forester SH S12 2009-2014 EJ255 EJ205
The hose flew off the manifold under the intercooler.
Click here to enlarge image -
Me, who knows so little about cars I've never changed my oil, fixed this with an $11 can of Mass Air Flow Sensor Cleaner from Autozone in 20 minutes. Look it up on Youtube its worth a try and it worked for me.
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I was getting the dreaded double whammy CEL light with these two codes.
My mechanic was pretty sure it was the O2 sensor (no leak in manifold).
I found that spraying a good dose of P26 Penrite throttle cleaner down the PCV line a left to sit for 5min on the PCV valve cleaned her out and stopped the CEL lights instantly. As my vehicle (BRZ 2014) hadn’t had the PCV valve checked or cleared in a long time and running into a catch can; it seems it may have gummed up a bit. The PCV is in a prick of a place so I’m trying to clean it out as much as possible.
Hope this helps anyone out a little as it’s a good quick easy task which may avoid the need to buy mega expensive bits which may not be required. If this doesn’t work, at least you’ve cleaned out the PCV and know one less bit is an issue before having to get a mechanic tackle the difficult and expensive repairs.
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