Search any generic check engine code: meaning, causes, and typical fix cost
| Code | Meaning | Typical Fix Cost |
|---|---|---|
| P0300 | Random / multiple cylinder misfire detected | $150–$600 (plugs, coil); more if injector or compression |
| P0301 | Cylinder 1 misfire | $100–$500 |
| P0302 | Cylinder 2 misfire | $100–$500 |
| P0303 | Cylinder 3 misfire | $100–$500 |
| P0304 | Cylinder 4 misfire | $100–$500 |
| P0305 | Cylinder 5 misfire | $100–$500 |
| P0306 | Cylinder 6 misfire | $100–$500 |
| P0327 | Knock sensor 1 circuit low (bank 1) | $250–$600 |
| P0335 | Crankshaft position sensor A circuit | $200–$500 |
| P0340 | Camshaft position sensor A circuit | $200–$500 |
| Code | Meaning | Typical Fix Cost |
|---|---|---|
| P0171 | System too lean (bank 1) | $100–$500 (vacuum leak, MAF, fuel delivery) |
| P0172 | System too rich (bank 1) | $150–$700 |
| P0174 | System too lean (bank 2) | $100–$500 |
| P0175 | System too rich (bank 2) | $150–$700 |
| P0101 | Mass air flow circuit range / performance | $150–$400 (often just cleaning) |
| P0102 | Mass air flow circuit low input | $150–$400 |
| P0106 | MAP / barometric pressure circuit range | $150–$450 |
| P0121 | Throttle position sensor A range / performance | $120–$400 |
| P0128 | Coolant thermostat below regulating temperature | $250–$550 |
| P0087 | Fuel rail / system pressure too low | $200–$1,200 (pump or HPFP) |
| Code | Meaning | Typical Fix Cost |
|---|---|---|
| P0131 | O2 sensor circuit low voltage (bank 1 sensor 1) | $150–$400 |
| P0133 | O2 sensor circuit slow response (bank 1 sensor 1) | $150–$400 |
| P0135 | O2 sensor heater circuit (bank 1 sensor 1) | $150–$400 |
| P0141 | O2 sensor heater circuit (bank 1 sensor 2) | $150–$400 |
| P0155 | O2 sensor heater circuit (bank 2 sensor 1) | $150–$400 |
| P0113 | Intake air temp sensor circuit high | $100–$300 |
| P0118 | Engine coolant temp sensor circuit high | $150–$350 |
| P0500 | Vehicle speed sensor A | $200–$500 |
| P0505 | Idle air control system | $150–$600 |
| P0507 | Idle control system RPM higher than expected | $100–$500 (often throttle-body cleaning) |
| P0562 | System voltage low | $400–$900 (alternator) |
| Code | Meaning | Typical Fix Cost |
|---|---|---|
| P0420 | Catalyst efficiency below threshold (bank 1) | $150–$400 (O2) · $1,300–$3,000+ (converter) |
| P0430 | Catalyst efficiency below threshold (bank 2) | $1,300–$3,000+ (converter) |
| P0401 | EGR flow insufficient | $150–$700 |
| P0402 | EGR flow excessive | $150–$700 |
| P0404 | EGR circuit range / performance | $150–$600 |
| P0410 | Secondary air injection system malfunction | $200–$800 |
| P0440 | EVAP system malfunction | $100–$500 |
| P0441 | EVAP incorrect purge flow | $150–$450 |
| P0442 | EVAP small leak detected | $100–$450 |
| P0446 | EVAP vent control circuit | $150–$400 |
| P0455 | EVAP large leak detected (check the gas cap) | $15–$50 (cap) · $100–$500 (otherwise) |
| P0456 | EVAP very small leak | $100–$450 (smoke test) |
| P0496 | EVAP high purge flow (stuck purge valve) | $150–$400 |
| Code | Meaning | Typical Fix Cost |
|---|---|---|
| P0010 | Camshaft position actuator circuit (bank 1) | $200–$600 |
| P0011 | Camshaft timing over-advanced (bank 1) | $200–$700 (oil change first) |
| P0014 | Camshaft timing over-advanced, exhaust (bank 1) | $200–$700 |
| P0016 | Crank / cam position correlation (bank 1 sensor A) | $200–$1,000+ (worst case: chain) |
| P0234 | Turbocharger / supercharger overboost | $150–$800 (wastegate, solenoid) |
| P0299 | Turbocharger / supercharger underboost | $100–$400 (leak) · $1,200–$3,000 (turbo) |
| P0700 | Transmission control system malfunction | diagnostic code: read TCM subcodes |
| P0730 | Incorrect gear ratio | $250–$2,500+ |
| P0740 | Torque converter clutch circuit open | $150–$2,500+ |
| P0741 | Torque converter clutch stuck off | $400–$2,500+ |
| P0751 | Shift solenoid A stuck / performance | $250–$800 |
Cost bands are typical US independent-shop ranges for the most common fix, parts plus labor; dealer rates and hard-to-reach sensors run higher. Tap any code in a table to decode it above. Codes starting P1 or P2 are manufacturer-specific and vary by make; the generic P0 set here applies across all makes sold in the US since the 1996 OBD2 mandate.
Every car and light truck sold in the US since 1996 reports faults through a standardized onboard diagnostics port. When the computer sees a reading outside its calibrated range for long enough, it stores a five-character diagnostic trouble code (DTC) and usually turns on the check engine light. Generic P0 codes follow the SAE J2012 standard, so P0420 means the same thing on a Toyota, a BMW, and a Ford.
The first letter is the system: P for powertrain, B for body, C for chassis, U for network. The second digit is 0 for generic codes or 1 for manufacturer-specific. The third digit is the subsystem: 1 covers fuel and air metering, 3 covers ignition and misfires, 4 covers auxiliary emissions, 5 covers idle and speed control. The last two digits point at the specific fault. So P0301 reads as generic powertrain, ignition/misfire, cylinder 1.
Read the code with a $25 Bluetooth adapter and a phone app, or get it read free at most parts stores. Type it into the search box above (or tap it in a table) to get the meaning, the usual suspects in order of likelihood, and a realistic repair-cost band. One rule worth internalizing: fix any misfire, lean, or rich code before touching a P0420 or P0430. Those codes say the converter isn't cleaning efficiently, and something upstream is often the reason.
Say a 2012 sedan books around $6,200 and throws P0420 with no other codes. The downstream O2 sensor is the cheap suspect: $150 to $400 installed. The converter is the expensive one: $1,300 to $3,000+ for a CARB-compliant or OEM-grade direct-fit unit. A $1,450 direct-fit converter on a $6,200 car is a 23.4% repair ratio (1,450 ÷ 6,200), which most people would fix. The same quote on a $2,500 car is 58%, and the honest math shifts toward driving it until the next problem, since a functioning converter matters for emissions testing and nothing else in daily driving. Price the full job with our catalytic converter cost calculator before deciding.
One more note that saves people real money: gutting or deleting the converter is a federal offense for any vehicle used on public roads, regardless of state inspection rules, and shops face four-figure fines per tampering event. Legitimate paths are an OE or CARB-compliant replacement, or in California and New York, a converter specifically certified for your engine family.
P0420, Catalyst System Efficiency Below Threshold (Bank 1), is the single most searched check-engine code. It means the computer sees the catalytic converter underperforming. Sometimes it is just a lazy downstream O2 sensor ($150 to $400), but a degraded converter usually runs $1,300 to $3,000 or more to replace at a shop.
A steady light with no drivability change is usually fine for a short drive, but get the code read within a few days. A flashing light means an active misfire dumping raw fuel into the catalytic converter, and driving on it can turn a $200 plug job into a $2,000 converter job. Pull over and address it.
The first letter is the system: P powertrain, B body, C chassis, U network. The second digit tells you if it is generic (0, standardized by SAE across all makes) or manufacturer-specific (1). The third digit is the subsystem, like 1 for fuel and air metering, 3 for ignition or misfires, 4 for auxiliary emissions. The last two digits identify the specific fault.
Yes, if the fault stops occurring. Most cars need 40 to 80 warm-up cycles without the problem recurring before the light turns off and the monitor resets. A hard fault like a dead sensor will keep the light on until it is fixed and the code is cleared with a scanner.
Clearing is a reasonable first diagnostic step for a single stale code, not a fix. Note that clearing also wipes the emissions readiness monitors, which means your car will fail a state inspection until several drive cycles re-set them. If the code returns within a few drives, the fault is real.
Nothing if you do it yourself. A basic Bluetooth OBD2 adapter costs $20 to $40 and pairs with a free phone app to read and clear generic codes. Many parts stores read codes for free, and shops typically charge half an hour to an hour of labor ($75 to $150) for diagnosis, often waived if you have the repair done.