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.
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.
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.
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:
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:
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.
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:
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.
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.
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