2002 Nissan Altima P0172 Code: Rich Fuel Mixture Diagnosis and Solutions
I own a 2002 Nissan Altima SL 2.5L, 4-cylinder, automatic transmission. Recently installed a used engine and replaced the Mass Air Flow (MAF) sensor. While cruising at high speeds, I notice a slight misfire or roughness in the engine. The OBD2 scanner shows code P0172, which indicates a rich fuel mixture. Possible causes include a faulty MAF sensor, oxygen sensor failure, vacuum leak, clogged injectors (I've already used Sea Foam), or low fuel pressure. I'm seeking advice on how to properly diagnose and resolve this issue without further damage.
Are there any other diagnostic codes present? What condition do the spark plugs show? (e.g., fouling, color) Perform a fuel pressure leak-down test to check for issues. Verify that the Engine Coolant Temperature (ECT) sensor is registering engine temperature at around 195°F. Check the fuel trim values in the ECU — are they showing rich readings? Is the air filter clean and properly installed? Ensure it's the correct one. Vacuum leaks typically cause lean conditions, not rich mixtures. Double-check that you're referring to MAF (Mass Air Flow) sensor, not MAS (which is likely a misstatement).