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  • Diagnostic trouble code (DTC) P0170 stands for “Fuel Trim Malfunction (Bank 1).” This means that the fuel trims in your vehicle have reached an abnormally low or abnormally high value for a specified amount of time. Most vehicles won’t set this code but may set other P017x codes.
  • Common causes of the P0170 code include contaminated engine oil, a leaking injector, and excessive fuel pressure.
  • Symptoms of the P0170 code include an illuminated check engine light, low fuel mileage, and hesitation when accelerating.

To ensure the air-fuel ratio of the mixture burns as efficiently as possible, the powertrain control module (PCM) tweaks the vehicle’s fuel trim over short and long periods. If the computer cannot properly adjust the air-fuel mix, it will log the diagnostic trouble code P0170.

What Does the P0170 Code Mean?

Diagnostic Trouble Code (DTC) P0170 stands for “Fuel Trim Malfunction (Bank 1).” Fuel trim is the adjustment made by the PCM to the engine’s air-fuel mixture. The P0170 code indicates that the fuel trims have reached an abnormally low or abnormally high value for a specified amount of time.

This code is one of a series of codes related to fuel trim. Note that most vehicles won’t set this code but may set other P017x codes, so you may never see this exact code. For a technical understanding of fuel trim, you can read our in-depth explanation here.

, P0170 Code: Fuel Trim (Bank 1)

Pro Tips are nuggets of information direct from ASE-certified automobile technicians working with, which may include unique, personal insights based on their years of experience working in the automotive industry. These can help you make more informed decisions about your car.

Pro Tip: Bank 1 is either the only bank (as in with an in-line 4 cylinder) or the bank where #1 cylinder is located on a 6 cylinder or a V8.

The ECM/PCM and the O2 sensor are all about keeping things balanced in the combustion chamber. If the mixture drifts too far out of balance, a code like P0170 is stored. You can learn more about this process here.

Note: Code P0170 is a generic code defined by the Society of Automotive Engineers (SAE). The vehicle’s manufacturer may set a different definition for the code.

diesel fuel injector
If the computer cannot properly adjust the air-fuel mix, it will log the diagnostic trouble code P0170.

What are the Possible Causes of the P0170 Code?

Like any other OBD-II code, a P0170 can be caused by a variety of problems. In other words, there is no easy way to pinpoint what’s causing the problem other than examining the critical parts responsible for maintaining the right fuel mixture.

The PCM may log the P0170 code for the following reasons:

  • Contaminated Engine Oil (too long since the last oil change)
  • A leaking injector
  • Excessive fuel pressure due to restriction along the fuel return line or a faulty fuel pressure regulator
  • A saturated Carbon Canister due to packing the fuel tank.
  • Clogged air filter
  • Restrictions somewhere else in the air intake system
  • Clogging due to buildup or physical damage in these exhaust components: catalytic converter, exhaust pipe, and muffler
  • Faulty O2 sensor (but O2 sensors more commonly fail by reading lean, not rich).
  • Exhaust leak
  • Problems with other sensors (e.g., engine coolant temperature sensor, mass airflow sensor)
  • Circuit issues, such as loose connections and damaged wiring
  • Issues with the PCM, such as software in need of an update

What are the Common Symptoms of the Engine Code P0170?

The fuel trim directly affec

ts the engine’s performance. If the fuel trim runs into a problem that forces the PCM to log a P0170 code, the following symptoms may appear:

  • An illuminated or blinking Check Engine Light
  • The vehicle’s fuel mileage drops because of wasted fuel
  • The engine suffers from hesitation when the vehicle accelerates
  • The engine misfires and runs rough
  • The engine stalls and/or has a rough idle

Many instances of a malfunctioning fuel trim on bank 1 will not come with noticeable warning signs. For those cases, you may only realize you have a P0170 code on your hands after you plug your OBD scanner into your vehicle.

oxygen sensor 7
The stoichiometric mixture best suited for burning is 14.7 parts air to 1 part fuel.

How to Diagnose the P0170 Code

For most car owners, a P0170 code calls for a trip to a reliable auto repair shop, where trained experts can get to the bottom of the problem. Car owners with extensive experience and skill in DIY car repair can diagnose their vehicle and repair whatever disrupted the fuel trim and forced the PCM to log the P0170 code.

If you want to refresh your knowledge of this diagnostic trouble code, you can watch the following video detailing possible causes of the P0170 code:

How to Fix the P0170 Code

There’s no single fix for the P0170 code, just like most OBD-II codes. This is why it might be better to let a licensed mechanic do the fixing for you.

If you want to resolve the code yourself, you can use repair manuals or online auto repair resources and guides to help you figure out the proper fix. As always, check your owner’s manual before attempting any repair.

Finally, remember that different manufacturers may have different repair instructions for their respective vehicles and that a fix that works in one particular model may not work for others, especially those from a different manufacturer.

Other Notes About P0170

The P0173 code indicates a fuel trim malfunction for the opposite side (bank 2) of the engine. It’s otherwise identical to the P0170 code.

In 2008, Mercedes-Benz parent company Daimler AG issued the Campaign 2008020002 – Vent Hose. The technical service bulletin (TSB) warned that the crankcase vent hose mounted below the intake manifold of several MB models can develop cracks that may lead to leaks and rough running. A cracked or leaking hose can drive the PCM to log a P0170 code.

Where to Get Replacement Parts for Your Vehicle 

When it comes to shopping for replacement air filters, fuel pressure regulators, or oxygen sensors, has you covered.

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About The Authors
Written By Automotive and Tech Writers

The Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Reviewed By Technical Reviewer at

Richard McCuistian has worked for nearly 50 years in the automotive field as a professional technician, an instructor, and a freelance automotive writer for Motor Age, ACtion magazine, Power Stroke Registry, and others. Richard is ASE certified for more than 30 years in 10 categories, including L1 Advanced Engine Performance and Light Vehicle Diesel.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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