Poor fuel economy: Codes, Causes & Fixes

P0420 Powertrain The bank 1 catalytic converter no longer stores enough oxygen to clean the exhaust properly. Low P0101 Powertrain The MAF sensor's airflow reading doesn't match what the engine computer expects… Low P0113 Powertrain The intake air temperature signal is stuck at maximum voltage, which usually means an open… Low P0135 Powertrain The heater inside the upstream oxygen sensor on bank 1 isn't working or its circuit is faulty. Low P0172 Powertrain The engine computer is pulling as much fuel as it's allowed on bank 1 and the mixture is still… Moderate P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High

P0128 Powertrain The engine takes too long to warm up, which almost always points to a thermostat stuck open. Low P0130 Powertrain The upstream oxygen sensor on bank 1 sent a signal the engine computer could not make sense of. Low P0131 Powertrain The upstream oxygen sensor on bank 1 keeps reporting a voltage so low that it reads as a lean… Low P0132 Powertrain The upstream oxygen sensor on bank 1 reads too high: the engine is running rich or the signal… Moderate P0133 Powertrain The upstream oxygen sensor on bank 1 still works, but it reacts to mixture changes too slowly. Low P0134 Powertrain The upstream oxygen sensor on bank 1 isn't switching at all: its signal stays flat after… Low P0135 Powertrain The heater inside the upstream oxygen sensor on bank 1 isn't working or its circuit is faulty. Low P0150 Powertrain The upstream O2 sensor circuit on bank 2 is sending readings the ECU can't use, usually wiring… Low P0151 Powertrain Bank 2's front O2 sensor is stuck at a lean reading – often a manifold leak on that side… Low P0153 Powertrain Bank 2's front O2 sensor still switches, but too slowly between rich and lean; usually aged… Low P0154 Powertrain Bank 2's front O2 sensor never started switching; the ECU sees only a flat voltage from it. Low P0155 Powertrain The heater in bank 2's front O2 sensor, or its fuse, power feed or ECU-controlled ground, has… Low P0157 Powertrain The O2 sensor after the bank 2 converter reads near zero volts – often a nearby exhaust leak… Low P0158 Powertrain The O2 sensor after the bank 2 converter reads too high – often a short to heater power… Low P0170 Powertrain Bank 1 fuel correction is far outside its normal window, lean or rich, and the ECU won't say… Moderate P0172 Powertrain The engine computer is pulling as much fuel as it's allowed on bank 1 and the mixture is still… Moderate P0173 Powertrain Fuel correction on bank 2, the side without cylinder 1, is out of range or unstable, lean… Moderate P0175 Powertrain Bank 2 is still running rich even though the PCM is already cutting fuel on that side as far as… Moderate P0181 Powertrain The fuel temperature reading is electrically fine but doesn't match the engine's other… Low P0206 Powertrain Injector 6's circuit is open or faulty. On an inline-six that's the rear cylinder, tucked under… Moderate P0208 Powertrain The circuit to injector 8, the rear cylinder on bank 2 of a V8, is open or doesn't respond… Moderate P0266 Powertrain The engine computer can't even out cylinder 2 with fuel corrections; its balance rate is past… Moderate P0272 Powertrain The ECU can't balance cylinder 4 against the rest anymore; its fuel correction is outside… Moderate P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High P0303 Powertrain Cylinder 3 is misfiring. Check whether it misses at idle or under load before you blame… Moderate P0325 Powertrain The computer isn't getting a usable signal from knock sensor 1, so it pulls timing to protect… Low P0326 Powertrain Knock sensor 1 works electrically, but what it hears doesn't match what the computer expects. Low P0327 Powertrain Knock sensor 1's signal is too weak or pulled to ground: usually wiring, water or a loose… Low P0328 Powertrain Knock sensor 1's signal is too strong: a short to voltage, electrical noise or a genuinely… Low P0330 Powertrain The second knock sensor, usually the one for the bank without cylinder 1, has a circuit fault. Low