P0172 - System Too Rich Bank 1 | Read Negative Fuel Trim First

P0172: System Too Rich (Bank 1) The engine computer has reached the limit of how much fuel it can subtract to correct a rich reading on bank one; the code does not automatically mean an oxygen sensor failed. Full written guide, diagrams and cost tables: https://www.freezeframecode.com/codes/p0172/ CHAPTERS 00:00 What this code means 00:39 How the test actually works 01:37 Symptoms 02:33 Most likely causes, ranked 04:24 The measurement that decides it 05:26 Diagnostic order 07:33 Repair costs 08:54 Recap and related codes MOST LIKELY CAUSES Leaking or over-delivering fuel injector (27%) Stuck-open EVAP purge valve or excess fuel vapor (20%) Fuel pressure too high or regulator fault (18%) MAF, MAP or airflow calculation biased high (14%) Upstream oxygen or air-fuel sensor biased rich (12%) Incorrect fuel learning, injector coding or PCM calibration (9%) TYPICAL REPAIR COST EVAP purge valve: $25-$180 in parts, about 0.7h labor Injector cleaning, seals or required relearn: $20-$250 in parts, about 1.0h labor Single fuel injector: $60-$450 in parts, about 1.5h labor Fuel-pressure regulator or supply component: $40-$1200 in parts, about 2.0h labor MAF, MAP or upstream air-fuel sensor: $50-$500 in parts, about 0.8h labor RELATED CODES P0175, P2196, P0300, P0441, P0191 --- This video is general reference information, not a repair authorization for your specific vehicle. Always confirm procedures and torque values against the factory service manual for your exact year, make, model and engine before doing any work. Diagnosis order assumes a scan tool that can read live data and freeze frame.