Generic OBD2 code · Fuel and air metering

P0170: Fuel Trim (Bank 1)

The engine computer has adjusted the fuel mixture on bank 1 as far as it is allowed and still cannot reach the correct air fuel ratio.

CodeP0170

SystemFuel and air metering

Typical urgencyModerate to high

Can I keep driving?Usually drivable, but power and fuel economy can suffer and long term the catalytic converter can be damaged. Diagnose it soon.

What does P0170 mean?

Short and long term fuel trim are the corrections the engine computer makes to keep the air fuel mixture near the ideal ratio. P0170 sets when those corrections reach their limit, either adding or removing fuel.

Unlike P0171 (too lean) or P0172 (too rich), P0170 does not say which way the mixture is off. Live fuel trim values show whether the computer is adding or removing fuel.

Common symptoms

Check engine light on
Lower fuel economy
Hesitation or loss of power
In many cases no obvious symptoms

Common causes

The causes below are the ones commonly seen with P0170. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

Intake or vacuum leaks
A faulty mass airflow sensor or its wiring
Fuel delivery problems such as a weak fuel pump or faulty fuel pressure regulator (listed by YourMechanic)

What to check with a scanner

In Live data, read short and long term fuel trim for bank 1 at idle and at 2,500 rpm. Large positive values mean the computer is adding fuel; large negative values mean it is removing fuel.
Read freeze frame data for load and rpm when the code set.
Check intake hoses and the airflow sensor connector.
Note P0171 or P0172 if present, as they show the direction of the problem.

How to read and clear P0170 with OBD Master Pro

Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0170 is listed and note any other codes, since they often explain the cause.
Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0170 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0170.

When to see a mechanic

Get professional help if any of these apply:

You suspect a vacuum leak but cannot find it
Fuel pressure needs testing
The engine misfires or the check engine light flashes

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

P0170 FAQ

What is fuel trim?

It is the correction the engine computer makes to the planned fuel amount, based on oxygen sensor feedback.

How is P0170 different from P0171?

P0171 means the mixture is too lean. P0170 only says the trim limit was reached, so you need fuel trim data to see the direction.

Can a vacuum leak cause P0170?

Yes. RepairPal lists intake manifold vacuum leaks among the common causes.

Check P0170 on your own car

OBD Master Pro turns your Android phone and a generic ELM327 adapter into a code reader: read and clear codes, view freeze frame and live data, and check emissions readiness.

Sources

Published October 24, 2026. Updated October 24, 2026. This guide is general information for generic SAE codes. Always follow the service information for your specific vehicle.