Trouble Code P0170: Fuel Trim Malfunction (Bank 1)

Troubleshooting vehicle problems requires patience, knowledge and the right kind of tools. When you’re diagnosing an OBD-II scanner error code P0170 problem, it’s important to know what this error code means. Generated by your vehicle’s on-board diagnostic system, a P0170 error usually means the problem lies in the powertrain assemblies. While this may seem a little vague, it can lead you to the root cause so you can rectify the issue.

What Does the Code P0170 Mean?

As indicated in the full error output message, a code P0170 points to a fuel trim malfunction. A proper fuel mixture is needed for a combustion engine to burn fuel without leaving behind excess air. In layperson’s terms, the fuel trim is an adjustment performed by a vehicle’s engine computer to ensure that this mixture consists of an optimal air/fuel ratio.

Each vehicle performs a fuel trim when its powertrain control module reads signals from the oxygen sensors and appropriately adjusts the engine’s level of fuel intake. Without this ability to change the air/fuel ratio, this mixture won’t be properly balanced. A code P0170 means that the PCM is either subtracting too much fuel and making the mixture too lean, or it’s adding too much fuel to make the mixture too rich.

Common Symptoms of Error Code P0170

A P0170 error occurs along with an improperly balanced fuel mixture. Your vehicle may display certain symptoms when your OBD-II scanner detects this error code:

• An illuminated “Check Engine” light
• Poor fuel economy
• Loss of power
• Frequent starting, stalling or stumbling
• Hesitating during acceleration
• Misfiring during idle or while under load
• Black smoke emitting from the tailpipe

What Causes a Fuel Trim Malfunction?

Fuel trim malfunctions can have a wide range of root causes. Vacuum, turbocharge air hoses or unmetered air leaks are a possible culprit. Engine oil that’s saturated with engine oil can trigger a P0170 error code, as well as oil contamination in either the mass airflow connector or O2 sensor connectors. Speaking of sensors, defective MAF or O2 sensors can prompt the OBD-II system to return a P0170 code. Oil may also intrude in the wiring harness if there’s a leakage in the ignition coils, cam and crank sensors or oil sensors. Other possible problems can include a defective fuel pressure regulator or leaking camshaft adjuster solenoids.

How Do I Fix Trouble Code P0170?

Fortunately, there are a few steps you can take to rectify a trouble code P0170. The most common malfunctions occur with the MAF sensor or the air mass meter, especially with Mercedes and other European vehicle makes. American vehicles tend to return other similar codes instead, including P0171, P0172, P0174 or P0175. Keep in mind that your OBD-II scanner tool may detect other concurring error codes. In those cases, you should ideally troubleshoot and diagnose the root causes of those other errors first.

Possible places to start troubleshooting include observing your vehicle’s MAF sensor readings and replacing the sensor if those readings are not within manufacturer specifications. Next, check for oil intrusions at the connector, measure fuel pressure, rule out external or internal regulator leaks. Inspect and replace any cracked, missing or faulty vacuum hoses. You should also look for vacuum leaks at the intake manifold gaskets or rips in the air supply hose. For turbocharged engines, inspect those hoses and replace any that have gone bad or are leaking.

Other Troubleshooting Considerations

After resolving the other issues, reset the Check Engine light and run the engine again. If you still receive a P0170 error, the likely root cause lies in the vehicle’s PCM. In those cases, the PCM may need to be replaced.