P0170

Fuel Trim (Bank 1)

Car Fault Codes Fuel & air

Can you still drive? With care, short trips only

Who can fix it? DIY with some experience

Typical repair time 30 minutes – 3 hours

Typical cost SAR 100 to 1,800

What it means

The engine computer constantly corrects the amount of fuel based on the oxygen sensor reading. This code means the correction on bank 1 has reached its limit or stayed outside the acceptable range, without the code itself saying whether the mixture is lean or rich, so the fuel trim values on a scan tool show the direction of the problem.

Symptoms4

Check engine light on.
Uneven or slightly rough idle.
Weak acceleration or hesitation.
Higher fuel use or a fuel smell from the exhaust if the mixture is rich.

Possible causes6

Vacuum leak from hoses or the intake manifold gasket.
Wrong readings from a dirty mass airflow (MAF) sensor.
Incorrect fuel pressure from the pump, filter or regulator.
A clogged or leaking injector.
Faulty upstream oxygen sensor giving an incorrect reading.
Exhaust leak ahead of the upstream oxygen sensor.

How to diagnose5

Read short- and long-term fuel trims; large positive values mean a lean mixture, large negative values mean a rich one.
Note whether the problem is worse at idle or at higher speeds; worse at idle suggests a vacuum leak.
Have a smoke test done on the intake manifold and vacuum hoses.
Compare the MAF reading with the expected value, and measure fuel pressure against the manufacturer specification.
On engines with two banks, compare bank 1 trims with bank 2 to see whether the cause is shared or on one side.

How to fix5

Replace the leaking vacuum hose or gasket.
Clean the MAF sensor with a dedicated cleaner, and replace it if readings stay wrong.
Fix the source of abnormal fuel pressure, such as the filter, pump or regulator.
Clean the injectors or replace a leaking one.
Clear the codes and confirm the fuel trims return to normal after driving.

Repair cost

0–500

500–2,000

2,000–5,000

5,000+

In Saudi riyals; the highlighted part is the expected range for this fault.

A vacuum leak or MAF cleaning costs little; the cost rises when the fuel pump or injectors are at fault.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions

What is the difference between P0170 and P0171?

P0171 says the mixture is lean, while P0170 means fuel trim is out of range without naming the direction; the technician finds it from the trim values on a scan tool.

Can I drive with this code?

For normal trips with care, but fix it soon, because an unbalanced mixture can cause misfires and damage the catalytic converter over time.

Was this explanation helpful?

Tap the stars to rate; you can change it later.

This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

Report a mistake

Spotted something inaccurate? Tell us and we will review and correct it.