OBD-II Code Types Explained - P, B, C, U Codes

The Four Types of OBD-II Codes

Every OBD-II diagnostic trouble code starts with a letter that tells you which vehicle system has the problem. P-codes (Powertrain) cover the engine, transmission, and drivetrain. B-codes (Body) cover interior systems like airbags, climate control, and lighting. C-codes (Chassis) cover the braking system, steering, and suspension. U-codes (Network) cover communication between the vehicle's computer modules.

Generic vs. Manufacturer-Specific Codes

The second character in the code tells you whether it's generic or manufacturer-specific. Codes starting with 0 (like P0300) are generic SAE codes that mean the same thing on every vehicle. Codes starting with 1 (like P1300) are manufacturer-specific and may have different meanings depending on whether you drive a Toyota, Ford, or GM vehicle. Codes starting with 2 or 3 can be either generic or manufacturer-specific depending on the specific code.

P-Codes: Powertrain (Most Common)

P-codes are by far the most common type, making up about 80% of all check engine light triggers. They cover everything from misfires (P0300-P0312) and oxygen sensors (P0130-P0167) to transmission problems (P0700-P0799) and fuel system issues (P0170-P0175). When your check engine light comes on, there's a high chance it's a P-code.

B-Codes: Body Systems

B-codes cover non-powertrain interior and exterior systems. These include airbag/SRS faults (B0001-B0099), lighting problems (B1000-B1099), HVAC/climate control issues (B1200-B1299), power window and door lock faults (B1300-B1399), and instrument cluster errors (B1400-B1499). B-codes usually don't trigger the check engine light but may trigger other warning lights like the airbag light.

C-Codes: Chassis Systems

C-codes cover the vehicle's braking, steering, and suspension systems. ABS faults (C0035-C0273), traction and stability control (C0196-C0242), power steering (C1200-C1260), and suspension/ride control (C1300-C1360) fall into this category. C-codes typically trigger the ABS or traction control warning light rather than the check engine light.

U-Codes: Network Communication

U-codes indicate communication problems between the vehicle's electronic control modules. Modern vehicles have dozens of computers that talk to each other over a CAN bus network. When one module can't communicate with another, a U-code is set. Common examples include U0100 (lost communication with ECM/PCM) and U0121 (lost communication with ABS module). These can be caused by wiring problems, failed modules, or a dead battery.

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