P-Codes (Powertrain)

OBD-II P-codes are the most common diagnostic trouble codes because they cover the systems that control drivability: engine performance, fuel/air delivery, misfires, emissions, and transmission operation. Use this hub to find your P-code faster, understand what it points to, and jump into the right repair guide.

Check Engine Light codes Fuel / Air / Ignition Emissions & EVAP Transmission

Find Your P-Code

If you already have the code, the fastest route is the Code Library. If you’re diagnosing by symptom (rough idle, misfire, poor MPG), use the system sections below.

Tip: The Code Library page is where the live lookup happens. This hub organizes P-codes by system and links to the most popular ones.

Flashing Check Engine Light? That can indicate an active misfire that may damage the catalytic converter. Reduce load and stop driving when safe if the vehicle is running poorly.

P-Code Sections (Browse by System)

P0100–P0199

Fuel & Air Metering

MAF/MAP readings, O2/AFR behavior, fuel trims, vacuum leaks, injector/fuel pressure problems.

Common: P0171 / P0174 (lean)

P0300–P0399

Misfire & Ignition

Random and cylinder-specific misfires, ignition coils, plugs, wiring, fuel delivery imbalance.

Common: P0300 / P0301–P0308

P0400–P0499

Emissions, Catalyst & EVAP

Catalyst efficiency, EGR, EVAP leaks, purge/vent issues, readiness monitor problems.

Common: P0420 / P0455

P0010–P0099

Engine Timing / VVT

Cam/crank correlation, VVT solenoids, oil control issues, timing chain/belt concerns.

Common: P0010 / P0011

P0200–P0299

Injector Circuits & Inputs/Outputs

Injector circuit faults, wiring/connector issues, cylinder fueling problems.

Common: P0201–P0208

P0700–P0999

Transmission

Shift solenoids, speed sensors, TCM faults, gear ratio errors, limp mode triggers.

Common: P0700 + companion codes

Fuel & Air Metering (P0100–P0199)

These codes often show up with rough idle, hesitation, poor fuel economy, or a “too lean/too rich” condition. Start with intake leaks, MAF/MAP readings, and fuel trim behavior.

P0171 — System Too Lean (Bank 1) How OBD Works — sensors, ECU logic, and why trims matter How to Use an OBD2 Scanner — fuel trims & live data basics

Misfire & Ignition (P0300–P0399)

Misfire codes can be ignition-related (plugs/coils), fuel-related (injectors/pressure), air-related (vacuum leaks), or mechanical. A flashing CEL is a strong hint of an active misfire.

P0300 — Random/Multiple Cylinder Misfire Detected P0301 — Cylinder 1 Misfire (example cylinder-specific guide) Beginner guide — stored vs pending vs permanent codes

Emissions, Catalyst & EVAP (P0400–P0499)

Emissions codes don’t always mean a bad catalytic converter. Exhaust leaks, upstream sensor issues, misfires, and fueling problems can all trigger efficiency codes.

P0420 — Catalyst System Efficiency Below Threshold Emissions readiness — monitors, drive cycles, and passing inspection Troubleshooting tips — common causes & safe checks

Engine Timing / VVT (P0010–P0099)

Timing-related codes often tie back to oil quality/level, VVT solenoids, actuator screens, or worn timing components. If timing performance codes appear with drivability symptoms, treat them as higher priority.

P0011 — Camshaft Timing Over-Advanced (Bank 1) How OBD Works — ECU logic and sensor correlation

Injector Circuits & Inputs/Outputs (P0200–P0299)

Injector circuit codes can cause misfires, fuel smell, and rough running. Wiring faults, connector issues, and injector failures are common—especially when a single cylinder is affected.

P0201 — Injector Circuit/Open (Cylinder 1) P0300 — Misfire guide (fuel + ignition checks)

Transmission (P0700–P0999)

P0700 is a generic “transmission control system” flag and usually appears with additional transmission codes that point to the real issue (solenoids, pressure, speed sensors, ratio errors).

P0700 — Transmission Control System Malfunction Code Library — search companion transmission codes

Want faster answers? If you share the exact code(s) and your vehicle year/make/model, you’ll get better results by checking companion codes and viewing freeze-frame data (if your scanner supports it).