Free OBD2 code lookup

What does your check engine code mean?

Type the code from your scanner. You get a plain-English explanation, what usually causes it, how a good tech would test it, and what the repair tends to cost.

Popular: P0420 P0300 P0171 P0455 P2463 P20EE

Popular codes

P0420Catalyst System Efficiency Below Threshold (Bank 1)$100 - $3,500P0300Random/Multiple Cylinder Misfire Detected$100 - $1,300P0171System Too Lean (Bank 1)$20 - $1,300P0128Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)$80 - $450P0455Evaporative Emission System Leak Detected (Large Leak)$15 - $700P0442Evaporative Emission System Leak Detected (Small Leak)$15 - $700P0401Exhaust Gas Recirculation Flow Insufficient Detected$100 - $1,500P0430Catalyst System Efficiency Below Threshold (Bank 2)$100 - $3,500P0174System Too Lean (Bank 2)$20 - $1,300P0507Idle Control System RPM Higher Than Expected$80 - $450P0101Mass or Volume Air Flow Sensor "A" Circuit Range/Performance$20 - $450P0335Crankshaft Position Sensor "A" Circuit$100 - $400P0340Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)$100 - $400P0700Transmission Control System (MIL Request)$150 - $5,500P0011"A" Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)$150 - $3,000P0301Cylinder 1 Misfire Detected$100 - $600

Diesel pickup codes

DPF, DEF and fuel pressure codes on Duramax, Cummins and Powerstroke trucks. See all diesel codes.

P2463Diesel Particulate Filter Restriction - Soot Accumulation$100 - $7,000P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)$50 - $6,000P0087Fuel Rail/System Pressure - Too Low$50 - $14,000P0299Turbocharger/Supercharger "A" Underboost Condition$100 - $5,000P242FDiesel Particulate Filter Restriction - Ash Accumulation$300 - $7,000P2002Diesel Particulate Filter Efficiency Below Threshold (Bank 1)$150 - $7,000P2BADNOx Exceedence - Root Cause Unknown$50 - $1,200P0093Fuel System Leak Detected - Large Leak$400 - $6,000P0401Exhaust Gas Recirculation Flow Insufficient Detected$100 - $1,500P20B9Reductant Heater "A" Control Circuit/Open$100 - $2,000

Repair cost estimator

Pick a repair and your vehicle type to get a realistic price range before you call a shop.

Dashboard warning lights

What each light means, what color tells you, and when you need to pull over.

DEF and DPF guide

How diesel emissions systems work, why regens fail, and how to avoid a derate.

Browse by system

Misfire and ignition24 codesFuel and air mixture25 codesFuel system35 codesOxygen sensors44 codesEmissions and catalytic converter14 codesEVAP system14 codesEngine sensors29 codesCooling system9 codesThrottle and pedal11 codesEngine timing and VVT16 codesTurbo and boost11 codesDiesel systems48 codesTransmission41 codesElectrical and modules19 codes

How to read an OBD2 code

Every OBD2 code has five characters. The letter is the system: P for powertrain (engine and transmission), B body, C chassis, U network. The first digit tells you whether it is a generic code (0, and most codes starting with 2) or a manufacturer-specific one (1, and some 3 codes). The remaining characters point to the system and the specific fault.

A code tells you which self-test failed, not which part is broken. P0420 does not always mean a bad converter, and P0171 is more often a vacuum leak than a bad oxygen sensor. That is why every page here walks through testing before parts.