P0170 Fuel trim: circuit fault (bank 1)

By: Diagno editorial team · Updated: 2026-10-15

P0170 means: Fuel trim: circuit fault (bank 1). The mixture has too little fuel or too much air, and the computer can no longer correct it on its own. Drive gently and have the car checked soon. The most common repair costs about €45–90 in Estonia, depending on make and model.

What it means

The mixture has too little fuel or too much air, and the computer can no longer correct it on its own. The computer found a fault in the electrical circuit: the part, a wire, a connector or a fuse.

What you may notice

• Engine light on
• Rough idle
• Hesitation when accelerating
• The engine may stall

What could be wrong

1. 1Connector loose, damp or corroded · Wiring or connector repair €45–90
2. 2Wire broken or chafed · Wiring or connector repair €45–90
3. 3Faulty sensor · Sensor replacement €80–160
4. 4Engine computer fault (rare) · Control unit check and software €150–300

Repair difficulty: Moderate

What you can check yourself

First look at the connector and wiring: anything loose, melted or green with corrosion? Listen at idle for a hiss. Check the vacuum hoses, especially old, cracked ones. You can check the simple things yourself, but the repair is best done in a workshop.

How we fix it

1. We read the fault data on the diagnostic tool and check whether the fault is constant
2. We measure the circuit's supply, ground and signal
3. We repair the wire or replace the connector
4. If the wiring is fine, we replace the sensor

Standard SAE description: Fuel Trim Malfunction (Bank 1)