System Too Rich (Bank 1)

Rich condition on Bank 1 is often caused by leaking fuel injectors. Perform a fuel injector balance test with a scan tool. Also check the MAP/boost pressure sensor for erroneous readings -- a cracked intercooler pipe causes overboosting. Clean the MAF sensor as a first step. Your dealer can confirm whether an open service bulletin or warranty extension applies to your VIN.

A dirty MAF sensor underreporting airflow is the most common cause of P0172 on the 2AR-FE. Clean with CRC MAF cleaner. If the code persists, check the fuel pressure regulator for a leaking diaphragm -- fuel will be present in the vacuum hose if it is failed. Also check the purge valve (Denso) for sticking open, which dumps fuel vapor into the intake. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.

Check for a stuck-open EVAP purge solenoid (ACDelco) which dumps fuel vapor into the intake manifold causing a rich condition. Use a scan tool to command the purge valve closed and monitor fuel trims. Also check for a leaking fuel pressure regulator. On 5.3L engines with AFM, excessive oil consumption can foul the O2 sensor causing false rich readings. Confirm the exact part for your year and engine with a retailer's fitment lookup or your VIN before ordering - these applications split by engine and build date.

Rich running on the N20/N26 is often caused by a failing high-pressure fuel pump (HPFP) not maintaining proper rail pressure. Check fuel pressure with a scanner -- should be 2000+ PSI at idle on direct injection. Also check the intake VANOS solenoid for oil sludge causing incorrect valve timing. BMW TSB SI B12 03 17 addresses fuel system diagnostics.