P2188 System Too Rich at Idle (Bank 1)

P2188 sets when bank 1 runs rich specifically at idle — the fuel trims pull a large negative correction at low load, pointing to excess fuel or a sensor that over-reports airflow at idle.

Code details

Generic OBD-II · P2

System: Fuel / Air
Code type: Generic (SAE / ISO controlled)
Standard: SAE J2012 / ISO 15031-6

Diagnostic boundary

A diagnostic trouble code reports that a monitored test failed. It does not prove one specific part is bad, and manufacturer logic can add vehicle-specific conditions.

Do not replace oxygen sensors first; confirm fuel pressure and injector behaviour, since the sensors are reporting a real rich condition at idle.

Symptoms of P2188

Rough idle and a rich exhaust smell.
Check-engine light with strongly negative idle trims.
Fouled plugs or poor economy.

Common causes of P2188

Leaking injectors or high fuel pressure.
A contaminated MAF over-reading airflow.
A leaking fuel-pressure regulator.
A saturated EVAP canister purging fuel vapour.

Useful checks before replacing parts

Check fuel pressure and look for leaking injectors at idle.
Inspect the MAF for contamination and compare it to expected idle airflow.
Look for a leaking fuel-pressure regulator or saturated charcoal canister.

Related OBD-II codes

These nearby fuel / air entries can help compare wording and pin down the fault area.