Fault codeP0173

MODERATE

Fuel Trim Malfunction (Bank 2)

What this code means

Fuel Trim Malfunction (Bank 2).

“Bank 1” is the side of the engine that holds cylinder number 1; “Bank 2” only exists on V and flat engines. An in-line engine has a single bank.

P0173 is a generic code: it means the same thing on every make. P0173 belongs to family P01xx — Fuel and air metering. Its page explains how to read a code and groups all its codes by part.

Mixture regulation (fuel trim)

The control unit constantly adjusts the amount of fuel injected according to the oxygen sensors: these corrections are the fuel trims, short term and long term. When it reaches its correction limit without getting the right mixture, it records one of these codes.

What you notice

Often hesitation, rough idle, higher consumption; sometimes nothing except the warning light.

How to check it

Klaro shows the short- and long-term trims. A long-term trim well above +10 % means the engine runs lean (air leak, weak fuel supply, dirty airflow sensor); well below −10 % means it runs rich (leaking injector, sensor reading wrong). Comparing the trims at idle and at 2,500 rpm helps tell an air leak from a fuel problem.

Watch it live in Klaro

With an OBD2 adapter plugged in, these live readings show the part at work, when your car reports them:

Short term fuel trim bank 1
Long term fuel trim bank 1
Short term fuel trim bank 2
Long term fuel trim bank 2
Mass air flow

What to do

Have it checked this week. The car remains usable, but the fault will not clear itself and will fail the roadworthiness test.

Clearing a code switches the light off but repairs nothing: if the fault remains, the code comes back. Clearing a fault code yourself →

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
73P0173