Fault codeP0175

MODERATE

System Too Rich (Bank 2)

What this code means

System Too Rich (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.

P0175 is a generic code: it means the same thing on every make. P0175 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.

Symptoms

Smell of petrol from the exhaust, black smoke under acceleration, rising consumption, black spark plugs, rough idle. The control unit sees too little oxygen in the exhaust and leans out up to its limit. Over time the excess fuel clogs the catalytic converter (P0420).

Common causes

Faulty mass airflow sensor, over-reading the air coming in
Injector leaking or stuck open
Fuel pressure too high: failed regulator, blocked return line
Coolant temperature sensor permanently reporting a cold engine (P0117, P0118)
Tired upstream oxygen sensor
Badly clogged air filter, or EVAP canister dumping its vapour

How to diagnose it

Look at the fuel trims: strongly negative at all revs, they confirm the excess fuel. Compare the displayed coolant temperature with reality once warm: a sensor stuck at 20 °C makes the engine inject as if it were starting up.

Then check fuel pressure with a gauge, ignition on and then engine running. A leaking injector often shows up as one spark plug blacker than the others. Test the airflow sensor by unplugging it: if the engine runs better without it, it is the culprit.

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 →

Repair cost

A temperature sensor: €15 to €50. An airflow sensor: €60 to €250. A pressure regulator: €40 to €150. An injector: €60 to €300 each.

How to read this code

PPowertrain
0standardised code
1Fuel and air metering
75P0175