What does my check engine code mean?
Plain-English guides to OBD2 trouble codes, with how serious each one is, likely causes, DIY checks, and when to see a mechanic. Every guide cites its sources.
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Popular codes
"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
P0011 means the engine computer commanded the Bank 1 'A' camshaft (usually the intake cam) to a certain variable valve timing posi…
P0014"B" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
P0014 means the engine computer commanded the Bank 1 'B' camshaft (usually the exhaust cam) to a certain variable valve timing pos…
P0016Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)
P0016 means the engine computer sees the crankshaft and the Bank 1 intake ('A') camshaft out of time with each other by more than …
P0017Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor B)
P0017 means the engine computer sees the crankshaft and the Bank 1 'B' camshaft (usually the exhaust cam) out of time with each ot…
P0030HO2S Heater Control Circuit (Bank 1, Sensor 1)
P0030 means the engine computer has found a fault in the heater control circuit of the front (upstream) oxygen sensor on Bank 1. A…
P0087Fuel Rail/System Pressure Too Low
P0087 means the engine computer saw fuel pressure at the fuel rail lower than it wanted. A low fuel level, a weak fuel pump, a clo…
P0089Fuel Pressure Regulator 1 Performance
P0089 means the engine computer has decided the fuel pressure regulator isn't keeping fuel pressure where it commanded. The regula…
P0100Mass Air Flow (MAF) Circuit Malfunction
P0100 means the engine computer has found a problem with the mass air flow (MAF) sensor or its circuit. The most common causes are…
P0101Mass Air Flow (MAF) Circuit Range/Performance
P0101 means the engine computer thinks the mass air flow (MAF) sensor's reading doesn't make sense compared with what it expects. …
P0102Mass Air Flow (MAF) Circuit Low
P0102 means the engine computer is seeing a signal from the mass air flow (MAF) sensor that is lower than it should be. The most c…
P0106MAP/Barometric Pressure Circuit Range/Performance
P0106 means the engine computer sees a manifold absolute pressure (MAP) or barometric pressure reading that doesn't make sense for…
P0113Intake Air Temperature (IAT) Sensor 1 Circuit High
P0113 means the engine computer is seeing a signal from the intake air temperature (IAT) sensor that is too high, which the sensor…
P0128Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
P0128 means the engine didn't reach its expected temperature within the expected time after starting. Most often the thermostat is…
P0135O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
P0135 means the engine computer has decided the heater inside the front (upstream) oxygen sensor on Bank 1 isn't working. A failed…
P0138O2 Sensor Circuit High Voltage (Bank 1, Sensor 2)
P0138 means the downstream oxygen sensor (after the catalytic converter) on Bank 1 is reporting a voltage that stays too high for …
P0141O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2)
P0141 means the engine computer has decided the heater inside the downstream (after the catalytic converter) oxygen sensor on Bank…
P0171System Too Lean (Bank 1)
P0171 means the oxygen sensor on Bank 1 sees too much oxygen in the exhaust, and the engine computer can't add enough fuel to hold…
P0172System Too Rich (Bank 1)
P0172 means the oxygen sensor on Bank 1 sees too little oxygen in the exhaust: the mixture has too much fuel for the air, and the …
P0174System Too Lean (Bank 2)
P0174 means the upstream oxygen sensor on Bank 2 sees too much oxygen in the exhaust, and the engine computer has hit its limit on…
P0193Fuel Rail Pressure Sensor A Circuit High
P0193 means the engine computer is getting a fuel rail pressure sensor signal that reads too high. Most often it is the sensor its…
P0299Turbocharger/Supercharger "A" Underboost Condition
P0299 means the engine computer asked the turbocharger or supercharger for more boost than it actually delivered. Boost leaks, a f…
P0300Random/Multiple Cylinder Misfire Detected
P0300 means the engine computer has detected misfires that aren't limited to one cylinder, or that move between cylinders. It does…
P0301Cylinder 1 Misfire Detected
P0301 means the engine computer has detected that cylinder 1 isn't firing properly. The most common culprits are ignition parts (s…
P0302Cylinder 2 Misfire Detected
P0302 means the engine computer has detected that cylinder 2 isn't firing properly. Both sources say ignition problems (spark plug…
P0303Cylinder 3 Misfire Detected
P0303 means the engine computer has detected that cylinder 3 isn't firing properly. Worn spark plugs, plug wires or ignition coils…
P0304Cylinder 4 Misfire Detected
P0304 means the engine computer has detected that cylinder 4 isn't firing properly. Worn spark plugs, plug wires or ignition coils…
P0305Cylinder 5 Misfire Detected
P0305 means the engine computer has detected that cylinder 5 isn't firing properly. Worn spark plugs, plug wires or ignition coils…
P0306Cylinder 6 Misfire Detected
P0306 means the engine computer has detected that cylinder 6 isn't firing properly. OBD-Codes.com says it's most often an ignition…
P0312Cylinder 12 Misfire Detected
P0312 means the engine computer has detected that cylinder 12 isn't firing properly, or in RepairPal's words, isn't sufficiently c…
P0322Ignition/Distributor Engine Speed Input Circuit No Signal
P0322 means the engine computer (PCM) isn't getting a usable engine speed signal from the ignition, distributor or crankshaft posi…
P0325Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)
P0325 means the engine computer sees a problem in the circuit for knock sensor 1 (bank 1, or the only knock sensor). The cause can…
P0335Crankshaft Position Sensor "A" Circuit Malfunction
P0335 means the engine computer is seeing no signal, or a faulty signal, from crankshaft position sensor 'A'. The cause can be the…
P0340Camshaft Position Sensor "A" Circuit Malfunction
P0340 means the engine computer isn't getting a usable signal from camshaft position sensor 'A'. Because the code covers the whole…
P0341Camshaft Position Sensor "A" Circuit Range/Performance
P0341 means the engine computer is getting a camshaft position signal, but the signal doesn't match what it expects (out of range …
P0380Glow Plug/Heater Circuit "A"
P0380 means the engine computer has found a fault in glow plug circuit "A" on a diesel engine. Glow plugs heat the combustion cham…
P0401Exhaust Gas Recirculation (EGR) Flow Insufficient Detected
P0401 means the engine computer saw too little exhaust gas recirculation. Carbon-clogged EGR passages, a faulty DPFE sensor or a s…
P0420Catalyst System Efficiency Below Threshold (Bank 1)
P0420 means the engine computer thinks the catalytic converter on Bank 1 isn't cleaning the exhaust as well as it should. It compa…
P0430Catalyst System Efficiency Below Threshold (Bank 2)
P0430 is the Bank 2 version of P0420: the engine computer thinks the catalytic converter on the side of the engine without cylinde…
P0440Evaporative Emission (EVAP) Control System Malfunction
P0440 means the PCM found a problem in the EVAP system, which captures fuel vapor so it doesn't escape. Start with the gas cap, th…
P0441Evaporative Emission (EVAP) System Incorrect Purge Flow
P0441 means the PCM saw the wrong amount of purge flow in the EVAP system, the part that sends stored fuel vapor into the engine t…
P0442Evaporative Emission (EVAP) System Leak Detected (small leak)
P0442 means the EVAP system, which stores fuel vapor so it doesn't escape, has a small leak, as small as about 0.04 inch. Start wi…
P0446Evaporative Emission (EVAP) System Vent Control Circuit Malfunction
P0446 points at the EVAP vent valve, the valve on the charcoal canister that lets fresh air in and seals the system for its leak t…
P0455Evaporative Emission (EVAP) System Leak Detected (large leak / no purge flow)
P0455 means the EVAP system has a large leak or no purge flow. The most common fix is the gas cap: reseat it, clear the code, and …
P0456Evaporative Emission (EVAP) System Leak Detected (very small leak)
P0456 means the PCM found a very small leak in the EVAP system, which stores fuel vapor so it doesn't escape. The most common caus…
P0457Evaporative Emission (EVAP) System Leak Detected (fuel cap loose/off)
P0457 means the PCM found a leak in the EVAP system, most often a loose, damaged or missing gas cap. Check and reseat the cap firs…
P0496EVAP System High Purge Flow
P0496 means fuel vapor is being pulled from the EVAP system into the engine when it shouldn't be. The most common cause is a purge…
P0500Vehicle Speed Sensor "A" Malfunction
P0500 means the engine computer isn't getting a believable vehicle speed signal from the vehicle speed sensor (VSS). A dead speedo…
P0504Brake Switch A/B Correlation
P0504 means the engine computer sees the two signals from the brake light switch disagreeing with each other. The most common caus…
P0505Idle Air Control (IAC) System Malfunction
P0505 means the engine computer has a problem controlling idle speed through the idle air control (IAC) valve or motor. Stalling a…
P0507Idle Air Control System RPM Higher Than Expected
P0507 means the engine is idling faster than the computer wants it to. The most common culprits are an air or vacuum leak after th…
P0520Engine Oil Pressure Sensor/Switch Circuit
P0520 means the engine computer is getting a signal from the oil pressure sensor (or sender/switch) that's out of its normal range…
P0521Engine Oil Pressure Sensor/Switch Range/Performance
P0521 means the engine computer is seeing an unexpected reading from the oil pressure sensor: out of its normal range, or stuck at…
P0524Engine Oil Pressure Too Low
P0524 means the engine computer is reading oil pressure that's too low. That might be a real loss of oil pressure, which can wreck…
P0670Glow Plug Control Module Circuit
P0670 is a diesel-engine code: the engine computer has found a problem in the circuit of the glow plug control module, the part th…
P0671Cylinder 1 Glow Plug Circuit
P0671 is a diesel-engine code: the engine computer has found a fault in the circuit of the glow plug for cylinder 1, so that plug …
P0672Cylinder 2 Glow Plug Circuit
P0672 is a diesel-engine code: the engine computer has found a fault in the circuit of the glow plug for cylinder 2, so that plug …
P0673Cylinder 3 Glow Plug Circuit
P0673 is a diesel-engine code: the engine computer has found a fault in the circuit of the glow plug for cylinder 3, so that plug …
P0674Cylinder 4 Glow Plug Circuit
P0674 is a diesel-engine code: the engine computer has found a fault in the circuit of the glow plug for cylinder 4, so that plug …
P0683Glow Plug Control Module to PCM Communication Circuit
P0683 is a diesel-engine code: the engine computer (PCM) can't communicate with the glow plug control module, so it can't reliably…
P06DAEngine Oil Pressure Control Circuit/Open
P06DA means the engine computer (ECM or PCM) has found an electrical fault, usually an open or high-resistance circuit, in the eng…
P06DDEngine Oil Pressure Control Circuit Performance/Stuck Off
P06DD means the engine computer (ECM or PCM) has found that the engine oil pressure control system on a variable-pressure oil pump…
P0700Transmission Control System Malfunction
P0700 means the transmission computer (TCM) has found a fault and told the engine computer to turn on the check engine light. P070…
P2000NOx Trap Efficiency Below Threshold (Bank 1)
P2000 means the engine computer measured more NOx (nitrogen oxides) after the NOx trap than its programmed limit allows on Bank 1.…
P2002Diesel Particulate Filter (DPF) Efficiency Below Threshold (Bank 1)
P2002 means the engine computer thinks the diesel particulate filter (DPF) on Bank 1 isn't working within its limits, usually judg…
P2015Intake Manifold Runner Position Sensor/Switch Circuit Range/Performance (Bank 1)
P2015 means the engine computer is getting an out-of-range reading from the bank 1 intake manifold runner position sensor, which r…
P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)
P20EE means the engine computer has decided the SCR (selective catalytic reduction) catalyst on Bank 1 isn't removing enough nitro…
P2263Turbocharger/Supercharger Boost System Performance
P2263 means the engine computer sees that the turbocharger or supercharger boost system is not performing as expected. Boost leaks…
P2463Diesel Particulate Filter (DPF) Restriction - Soot Accumulation
P2463 means the engine computer has decided the diesel particulate filter (DPF) is restricted by built-up soot. It's a generic cod…
P250FEngine Oil Level Too Low
P250F means the engine computer (PCM) has decided the engine oil level is too low, based on the oil level sensor in or on the oil …
P253FEngine Oil Deteriorated
P253F means the engine computer (PCM or ECU) has decided the engine oil has deteriorated and needs changing. On most cars this is …
P2563Turbocharger Boost Control Position Sensor "A" Circuit Range/Performance
P2563 means the engine computer is not getting a believable signal from the sensor that reports the turbocharger's boost control p…
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