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Check engine light code lookup

Type the code your scanner or parts store gave you (for example P0300 or P0420) to see what it means, how urgent it is, what usually causes it and what the fix typically costs. 150 of the most common codes are covered.

All codes

Fuel, air and variable valve timing (P00xx)

Fuel and air metering (P01xx)

Fuel injectors and turbo (P02xx)

Ignition and misfires (P03xx)

Emissions controls (P04xx)

Speed, idle and sensors (P05xx)

Engine computer and outputs (P06xx)

Transmission (P07xx)

Transmission (P08xx)

P0841Transmission Fluid Pressure Sensor/Switch "A" Circuit Range/PerformanceSerious

Newer powertrain codes (P2xxx)

Network and communication (U codes)

How check engine light codes work

Every car and light truck sold in the US since the 1996 model year has an OBD-II computer system that watches the engine, transmission and emissions parts. When it finds a problem it stores a five character trouble code and turns on the check engine light. The code tells you which system the computer is unhappy with and roughly what it saw. It does not tell you which part to buy, so treat it as the starting point for a diagnosis, not the answer.

How to read a code like P0301

P (System letter): Which part of the vehicle the code belongs to. P is powertrain (engine and transmission), B is body, C is chassis and U is network.
0 (Code type): 0 means a generic code defined by SAE that means the same thing on every OBD-II vehicle. 1 means a manufacturer specific code that only that automaker defines.
3 (Subsystem): On older P0 codes this digit points to the area involved. 3 is ignition system or misfire.
01 (Specific fault): The exact problem. Here 01 means cylinder 1, so P0301 is a cylinder 1 misfire.

What the first letter means

P: Powertrain. Engine, transmission and related drivetrain parts, including fuel, ignition, emissions controls and the engine computer. This is the largest group and the codes most people see.
B: Body. Systems mostly inside the passenger compartment, such as airbags, seat belts, power seats, lighting and comfort features.
C: Chassis. Systems mostly outside the passenger compartment, such as brakes and ABS, steering and suspension.
U: Network and vehicle integration. Communication between the computers in the car. U codes usually mean one module stopped hearing from another over the vehicle network.

Generic vs manufacturer codes

P0, B0, C0, U0: Generic (global) codes defined by SAE. The same code means the same thing on any OBD-II vehicle.
P1, B1, C1, U1: Manufacturer specific (enhanced) codes. Look these up for your exact make, because the same number can mean different things on different brands.
P2: Generic powertrain codes. SAE added the P2 range when the P0 numbers filled up, so codes like P2096, P2135 and P2187 work the same on every brand.
B2, C2, U2: Manufacturer controlled body, chassis and network codes.
P3, U3: Mostly manufacturer controlled ranges.
B3, C3: Reserved for future use.

Steady, flashing or off?

Steady light: The computer has confirmed a fault. Most steady lights are not emergencies, but get the code read soon so a small problem does not grow.
Flashing light: Usually a severe misfire. RepairPal explains the light flashes when misfires are bad enough to damage the catalytic converter. Ease off and stop driving as soon as it is safe.
Light off but code stored: A pending or history code. It has been seen but not confirmed, or the problem went away. It is still useful information for a diagnosis.

Tips before you pay for a repair

Write down every code, not just the first one. Several codes together often point to one shared cause.
Note the freeze frame data if your scanner shows it. It records engine speed, load and temperature at the moment the code set.
Fix misfire and fuel trim codes before replacing an expensive catalytic converter, since they are a common reason converters fail.
Clearing a code turns the light off but does not fix anything, and it erases data the shop could have used.
Many auto parts stores will read codes for free, and a basic OBD-II reader plugs into the port under the dashboard within reach of the driver.