OBD-II Diagnostic Trouble Codes
Search 12,191 standardized diagnostic codes used by every vehicle sold in the United States since 1996.
How to Read an OBD-II Code
Every diagnostic trouble code follows the same structure. Here's how to break down code P0301 as an example.
Most Common OBD-II Codes
These are the codes mechanics and vehicle owners encounter most frequently. Click any code for full details.
| Code | Description | Category | Severity |
|---|---|---|---|
| P0128 | Coolant Thermostat Below Thermostat Regulating Temperature | Air Metering | Low |
| P0131 | O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1) | Emissions | Medium |
| P0133 | O2 Sensor Circuit Slow Response (Bank 1 Sensor 1) | Emissions | Medium |
| P0135 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) | Emissions | Medium |
| P0138 | O2 Sensor Circuit High Voltage (Bank 1 Sensor 2) | Emissions | Medium |
| P0141 | O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2) | Emissions | Medium |
| P0171 | System Too Lean (Bank 1) | Fuel System | Medium |
| P0172 | System Too Rich (Bank 1) | Fuel System | Medium |
| P0174 | System Too Lean (Bank 2) | Fuel System | Medium |
| P0300 | Random/Multiple Cylinder Misfire Detected | Ignition | High |
| P0301 | Cylinder 1 Misfire Detected | Ignition | High |
| P0302 | Cylinder 2 Misfire Detected | Ignition | High |
| P0303 | Cylinder 3 Misfire Detected | Ignition | High |
| P0304 | Cylinder 4 Misfire Detected | Ignition | High |
| P0335 | Crankshaft Position Sensor A Circuit | Ignition | High |
| P0340 | Camshaft Position Sensor Circuit (Bank 1) | Ignition | High |
| P0341 | Camshaft Position Sensor Circuit Range/Performance (Bank 1) | Ignition | High |
| P0401 | Exhaust Gas Recirculation Flow Insufficient | Emissions | Medium |
| P0411 | Secondary Air Injection System Incorrect Flow Detected | Emissions | Medium |
| P0420 | Catalyst System Efficiency Below Threshold (Bank 1) | Emissions | Medium |
| P0430 | Catalyst System Efficiency Below Threshold (Bank 2) | Emissions | Medium |
| P0440 | Evaporative Emission Control System Malfunction | Emissions | Low |
| P0442 | Evaporative Emission Control System Leak Detected (Small Leak) | Emissions | Low |
| P0446 | Evaporative Emission Control System Vent Control Circuit | Emissions | Low |
| P0455 | Evaporative Emission Control System Leak Detected (Gross Leak) | Emissions | Low |
| P0456 | Evaporative Emission Control System Leak Detected (Very Small Leak) | Emissions | Low |
| P0500 | Vehicle Speed Sensor Malfunction | Speed/Idle | Medium |
| P0505 | Idle Control System Malfunction | Speed/Idle | Medium |
| P0507 | Idle Control System RPM Higher Than Expected | Speed/Idle | Medium |
| P0700 | Transmission Control System Malfunction | Transmission | High |
Browse by Category
Select a category to view all codes in that system.
Powertrain Codes (P)
Engine, transmission, fuel system, ignition, and emissions codes. The most common type, covering everything under the hood.
| Code | Description | Possible Causes |
|---|---|---|
| P0001 | Fuel Volume Regulator Control Circuit/Open | Faulty fuel volume regulator; Wiring issues; ECM failure |
| P0002 | Fuel Volume Regulator Control Circuit Range/Performance | Fuel pressure regulator malfunction; Clogged fuel filter; Wiring |
| P0003 | Fuel Volume Regulator Control Circuit Low | Short circuit in wiring; Faulty regulator; ECM issue |
| P0004 | Fuel Volume Regulator Control Circuit High | Open circuit; Faulty regulator; ECM problem |
| P0005 | Fuel Shutoff Valve A Control Circuit/Open | Faulty fuel shutoff valve|Wiring issues|ECM failure |
| P0006 | Fuel Shutoff Valve A Control Circuit Low | Short circuit|Faulty valve|Damaged wiring |
| P0007 | Fuel Shutoff Valve A Control Circuit High | Open circuit|Faulty valve|Corroded connector |
| P0008 | Engine Position System Performance Bank 1 | Timing chain stretched|Faulty VVT solenoid|Low oil pressure |
| P0009 | Engine Position System Performance Bank 2 | Timing chain stretched|Faulty VVT solenoid|Low oil pressure |
| P0010 | A Camshaft Position Actuator Circuit (Bank 1) | Faulty VVT solenoid; Low oil pressure; Wiring issue |
Body Codes (B)
Airbags, seat belts, HVAC, lighting, power windows, mirrors, instrument panel, and anti-theft systems.
| Code | Description | Possible Causes |
|---|---|---|
| B0001 | Driver Frontal Stage 1 Deployment Control | Faulty airbag module; Clockspring; Wiring; Crash sensor |
| B0002 | Driver Frontal Stage 2 Deployment Control | SRS module issue; Wiring; Airbag unit failure |
| B0003 | Passenger Frontal Stage 1 Deployment Control | Faulty passenger airbag; Occupant sensor; Wiring |
| B0004 | Passenger Frontal Stage 2 Deployment Control | SRS module; Wiring harness; Connector |
| B0005 | Driver Side/Curtain Deployment Control | Side airbag module; Impact sensor; Wiring |
| B0006 | Passenger Side/Curtain Deployment Control | Side curtain module; B-pillar sensor; Wiring |
| B0007 | Passenger Side Stage 1 Deployment Control | Faulty passenger side airbag|Wiring |
| B0008 | Passenger Side Stage 2 Deployment Control | Faulty passenger side airbag stage 2 |
| B0010 | Driver Frontal Crash Sensor | Faulty front crash sensor; Wiring; Corroded connector |
| B0011 | Passenger Pretensioner Deployment Control | Faulty passenger pretensioner|Wiring |
Chassis Codes (C)
ABS, traction control, stability control, brakes, steering, suspension, and tire pressure monitoring.
| Code | Description | Possible Causes |
|---|---|---|
| C0021 | Wheel Speed Sensor Front Left Circuit | Faulty ABS sensor FL|Damaged tone ring|Wiring |
| C0022 | Wheel Speed Sensor Front Left Circuit Range/Performance | Contaminated sensor|Air gap issue|Damaged reluctor |
| C0025 | Wheel Speed Sensor Front Right Circuit | Faulty ABS sensor FR|Damaged tone ring|Wiring |
| C0026 | Wheel Speed Sensor Front Right Circuit Range/Performance | Contaminated sensor|Air gap|Damaged reluctor |
| C0029 | Wheel Speed Sensor Rear Left Circuit | Faulty ABS sensor RL|Damaged tone ring|Wiring |
| C0030 | Wheel Speed Sensor Rear Left Circuit Range/Performance | Contaminated sensor|Air gap|Damaged reluctor |
| C0033 | Wheel Speed Sensor Rear Right Circuit | Faulty ABS sensor RR|Damaged tone ring|Wiring |
| C0034 | Wheel Speed Sensor Rear Right Circuit Range/Performance | Contaminated sensor|Air gap|Damaged reluctor |
| C0035 | Left Front Wheel Speed Sensor Circuit | Faulty wheel speed sensor; Tone ring damage; Wiring; Bearing |
| C0040 | Right Front Wheel Speed Sensor Circuit | Bad wheel speed sensor; Wiring; Tone ring |
Network Codes (U)
CAN bus communication failures, lost communication between modules, and data link errors.
| Code | Description | Possible Causes |
|---|---|---|
| U0001 | High Speed CAN Communication Bus | CAN bus wiring short/open; Module failure pulling bus down |
| U0002 | High Speed CAN Communication Bus Performance | CAN bus intermittent; Loose connection; Corroded terminal |
| U0003 | High Speed CAN Communication Bus Open | CAN bus open circuit|Broken wire|Disconnected connector |
| U0004 | High Speed CAN Communication Bus Low | CAN-Low wire shorted or open |
| U0005 | High Speed CAN Communication Bus High | CAN-High wire shorted or open |
| U0006 | Medium Speed CAN Communication Bus | MS-CAN bus fault|Body control network issue |
| U0007 | Medium Speed CAN Communication Bus Performance | MS-CAN degraded|Noise|Intermittent connection |
| U0008 | Medium Speed CAN Communication Bus Open | MS-CAN open circuit|Broken wire |
| U0009 | Medium Speed CAN Communication Bus Low | MS-CAN Low wire fault |
| U0010 | Medium Speed CAN Communication Bus High | MS-CAN High wire fault |
What Are OBD-II Codes?
OBD-II (On-Board Diagnostics II) is a standardized system required in every car and light truck sold in the United States since 1996. When a sensor detects a problem, the vehicle's computer stores a diagnostic trouble code (DTC) and turns on the check engine light or another warning indicator.
A code scanner or OBD-II reader plugs into the 16-pin port under your dashboard (usually below the steering column) and reads these codes. Generic codes (starting with 0 in the second digit) are universal, they mean the same thing on a Toyota, Ford, BMW, or any other make. Manufacturer-specific codes (starting with 1) may vary between brands.
Frequently Asked Questions
What does the check engine light mean?
The check engine light (MIL, Malfunction Indicator Lamp) means your vehicle's computer has detected a problem and stored a diagnostic trouble code. It could be anything from a loose gas cap (P0442) to a catalytic converter failure (P0420). The only way to know for sure is to read the code with an OBD-II scanner.
How do I read OBD-II codes?
You need an OBD-II code reader or scanner. Plug it into the 16-pin OBD-II port under your dashboard (usually below the steering column, on the driver side). Turn the ignition to ON (don't start the engine), and the scanner will display any stored codes. Basic code readers cost $15-30 and work on any 1996+ vehicle. Many auto parts stores will scan codes for free.
Can I drive with the check engine light on?
A steady check engine light usually means a non-critical issue, you can drive to a shop, but get it checked soon. A flashing check engine light means a severe misfire that can damage your catalytic converter, pull over safely and get it towed. Never ignore a flashing CEL.
How do I clear OBD-II codes?
You can clear codes with an OBD-II scanner (most have a "Clear Codes" button) or by disconnecting the battery for 15-30 minutes. However, clearing codes without fixing the underlying problem means the code will return. If the issue triggered the check engine light, the light will come back on within a few drive cycles.
What's the difference between generic and manufacturer-specific codes?
Generic codes (P0xxx, where the second digit is 0) are defined by the SAE standard and mean the same thing on every vehicle. Manufacturer-specific codes (P1xxx, where the second digit is 1) are defined by individual automakers and may vary between brands. For example, P1131 means one thing on a Ford and something different on a Toyota.
What is a pending code?
A pending code means the vehicle's computer detected a potential issue during one drive cycle but hasn't confirmed it yet. If the same problem occurs again on the next drive cycle, it becomes a confirmed (stored) code and the check engine light turns on. Pending codes are useful for catching problems early before they trigger the CEL.
Will my car pass emissions with a check engine light?
No. In most states, a vehicle with the check engine light on will automatically fail an emissions inspection, regardless of what the code is. You must fix the problem, clear the code, and complete a full drive cycle before the emissions test. Some states also check that all OBD-II readiness monitors are "ready."
What vehicles are covered by OBD-II?
All gasoline vehicles sold in the United States since 1996 and all diesel vehicles since 1997 are required to have OBD-II. This includes cars, trucks, SUVs, and vans. Motorcycles, heavy-duty trucks (over 14,000 lbs GVWR), and vehicles manufactured before 1996 are not required to have OBD-II.