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

P0332 Powertrain Knock sensor 2 reads too low. On a V engine it's the bank without cylinder 1; on some fours… Low P0341 Powertrain The bank 1 cam signal lands at the wrong crank angle, often from a stretched chain or a sticky… Moderate P0346 Powertrain Bank 2's cam signal arrives out of position. On V6/V8s that often means a bank 2 chain, guide… Moderate P0352 Powertrain Coil B, normally on cylinder 2, has a circuit fault. Where cylinder 2 sits depends… Moderate P0365 Powertrain The exhaust cam sensor on bank 1 has lost its signal. Usually a heat-damaged sensor… Low P0366 Powertrain Bank 1 exhaust cam signal is out of position: chain stretch, a sticky exhaust phaser… Moderate P0400 Powertrain EGR flow doesn't match what the ECU expected, and the code doesn't say whether it's too much… Low P0401 Powertrain The ECU opened the EGR system but saw too little effect — the valve or its passages are likely… Low P0420 Powertrain The bank 1 catalytic converter no longer stores enough oxygen to clean the exhaust properly. Low P0421 Powertrain The close-coupled warm-up catalyst on bank 1, right behind the exhaust manifold, isn't working… Low P0422 Powertrain The main underfloor catalytic converter on bank 1 no longer stores enough oxygen to pass… Low P0430 Powertrain The bank 2 converter on a V6, V8 or split-exhaust engine isn't cleaning the exhaust well enough. Low P0507 Powertrain The engine idles faster than the computer's target – most often extra air is sneaking… Low P052E Powertrain The crankcase ventilation regulator isn't controlling crankcase pressure properly – often… Moderate P0597 Powertrain The electrically heated thermostat's heater circuit is open, so the ECU can't open it early… Low P0710 Powertrain The transmission computer lost a usable fluid temperature signal and is guessing… Low P0734 Powertrain Fourth gear (overdrive on four-speed units) doesn't hold the expected input-to-output speed… Moderate P0735 Powertrain Fifth gear slips or isn't fully applied; the TCM measures a ratio that doesn't fit 5th. Moderate P0740 Powertrain The computer found an open or faulty circuit to the torque converter clutch solenoid, so lockup… Low P0741 Powertrain The torque converter lockup clutch slips or won't engage when the computer commands it. Moderate P0743 Powertrain The TCC solenoid circuit shows an electrical fault such as a short, overcurrent or out-of-range… Low P0744 Powertrain Lockup control drops in and out: an intermittent TCC circuit, or on some makes a lockup… Moderate P0755 Powertrain The TCM detects an electrical problem with shift solenoid B, the second on/off shift valve. Moderate P0760 Powertrain A fault in shift solenoid C's circuit – usually means lost overdrive or upper gears, or limp… Moderate P0A1F Powertrain The module that manages the high-voltage battery failed its self-check or reports implausible… Moderate P0A7E Powertrain The high-voltage battery got too hot. A clogged cooling intake or dirty fan is the usual cause. Moderate P0A7F Powertrain The battery computer has calculated that the whole high-voltage pack has worn past its usable… Moderate P0A80 Powertrain The hybrid system sees weak or unbalanced modules in the high-voltage battery and flags… Moderate P1101 Chevrolet · Powertrain GM's engine computer found that measured airflow doesn't agree with what it expects. Low P1128 Jeep · Powertrain Your Jeep's PCM never switched bank 1 from preset fueling to O2-sensor feedback after… Low