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.
The stoichiometric mixture best suited for burning is 14.7 parts air to 1 part fuel. If the mixture contains excessive amounts of air, the PCM will add more fuel to balance out the lean mixture. Conversely, too much fuel leads to a rich mixture, and the computer compensates accordingly.
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.
What are the Possible Causes of the P0170 Code?
The PCM may log the P0170 code for the following reasons:
- Rich running condition (caused by a leaking injector, a faulty mass air flow sensor, etc.)
- Lean running condition (caused by a vacuum leak, a fuel delivery problem, etc.)
- Faulty oxygen sensor creating false lean or rich readings
- Exhaust leak creating false lean readings
- An issue 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 affects 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.
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.