OBD2 Trouble Code List — Meanings, Causes, Check Engine Light

P0300

Random/Multiple Cylinder Misfire Detected

The engine is misfiring across more than one cylinder. This is one of the most common reasons a check engine light flashes.…

P0301

Cylinder 1 Misfire Detected

Cylinder 1 is not firing consistently. The light often comes on after a stumble, rough idle, or a flash under load.…

P0302

Cylinder 2 Misfire Detected

Cylinder 2 is misfiring. The check engine light usually appears with roughness that you can feel in the cabin.…

P0303

Cylinder 3 Misfire Detected

Cylinder 3 misfire. Common after coil or plug service is overdue.…

P0304

Cylinder 4 Misfire Detected

Cylinder 4 is misfiring. Very common on 4-cylinder engines when a coil pack fails.…

P0420

Catalyst System Efficiency Below Threshold (Bank 1)

The catalytic converter on bank 1 is not cleaning exhaust as efficiently as the PCM expects. This is a top search OBD2 code worldwide.…

P0430

Catalyst System Efficiency Below Threshold (Bank 2)

Same idea as P0420, but on bank 2 of a V6/V8. The light usually appears without a dramatic driveability change.…

P0171

System Too Lean (Bank 1)

Bank 1 is running lean — too much air or not enough fuel. A very common check engine light on many brands.…

P0172

System Too Rich (Bank 1)

Bank 1 is running rich — too much fuel. The light often comes with black smoke, rich smell, or poor MPG.…

P0174

System Too Lean (Bank 2)

Bank 2 lean condition. Often paired with P0171 when the cause is shared (MAF or vacuum leak).…

P0175

System Too Rich (Bank 2)

Bank 2 is too rich. Frequently appears with P0172 when a shared sensor is lying.…

P0442

EVAP System Leak Detected (Small Leak)

A small evaporative emissions leak, often a loose gas cap. The light can take days of driving to return after you tighten the cap.…

P0455

EVAP System Leak Detected (Gross Leak / No Flow)

A large EVAP leak. Missing gas cap is the classic cause.…

P0456

EVAP System Leak Detected (Very Small Leak)

A very small EVAP leak. Harder to find than P0442 and often needs a smoke machine.…

P0128

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

The engine is not reaching normal temperature quickly enough. A stuck-open thermostat is the usual cause.…

P0401

EGR Flow Insufficient Detected

Exhaust gas recirculation flow is lower than commanded. Carbon-clogged EGR passages are extremely common.…

P0402

EGR Flow Excessive Detected

Too much EGR flow, often a valve stuck open. Idle can be terrible.…

P0135

O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)

The upstream oxygen sensor heater on bank 1 failed. The light can come on shortly after startup.…

P0141

O2 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

Downstream (post-cat) O2 heater circuit fault on bank 1.…

P0133

O2 Sensor Circuit Slow Response (Bank 1 Sensor 1)

The front O2 sensor is lazy. Aging sensors are the typical cause.…

P0500

Vehicle Speed Sensor (VSS) Malfunction

The PCM is not getting a plausible vehicle speed signal. Speedometer, ABS, and shift quality can all be affected.…

P0700

Transmission Control System Malfunction

A request from the transmission controller. P0700 is a pointer code — there is usually a more specific TCM code stored.…

P0101

Mass or Volume Air Flow Circuit Range/Performance

MAF sensor reading does not match expected airflow. Dirty MAF elements are a frequent cause.…

P0102

Mass or Volume Air Flow Circuit Low Input

MAF signal is too low. Unplugged sensor or torn intake hose after the MAF are classic.…

P0113

Intake Air Temperature Sensor 1 Circuit High

IAT circuit high, usually an open sensor or unplugged connector. The light may come on with a cold-running strategy.…

P0118

Engine Coolant Temperature Sensor 1 Circuit High

Coolant temp circuit high (often -40 reading). Fans, mixture, and gauge can all be wrong.…

P0325

Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)

Knock sensor circuit fault. The PCM may retard timing as a precaution, costing power.…

P0335

Crankshaft Position Sensor A Circuit Malfunction

Crank sensor circuit fault. This can cause no-start, stalling, or a sudden cut-out.…

P0340

Camshaft Position Sensor A Circuit Malfunction (Bank 1 or Single Sensor)

Cam sensor circuit fault. Start-up can take longer, or the engine may run in limp timing.…

P0440

EVAP System Malfunction

Generic EVAP system fault. Often accompanied by a more specific leak or purge code.…

P0122

Throttle/Pedal Position Sensor/Switch A Circuit Low

Throttle position signal is too low. Drive-by-wire cars may go into limp mode.…

P0507

Idle Air Control System RPM Higher Than Expected

Idle is higher than the PCM wants. Vacuum leaks and dirty throttle bodies are common.…

P0506

Idle Air Control System RPM Lower Than Expected

Idle is too low. Stalling at lights is a typical complaint.…

P0011

Camshaft Position Timing Over-Advanced or System Performance (Bank 1)

Variable valve timing on bank 1 is over-advanced. Oil control issues are the usual root cause.…

P0014

Camshaft Position Timing Over-Advanced or System Performance (Bank 1 Exhaust)

Exhaust cam timing over-advanced on bank 1. Same oil/solenoid story as P0011 on many engines.…

P2195

O2 Sensor Signal Biased/Stuck Lean (Bank 1 Sensor 1)

Upstream O2 looks stuck lean. Can be a sensor, exhaust leak, or a truly lean engine.…

U0100

Lost Communication With ECM/PCM A

Another module cannot talk to the engine computer on the CAN bus. This is a network code, not a spark plug code.…

U0140

Lost Communication With Body Control Module

Lost comms with the BCM. Interior electronics, lights, or locks may misbehave along with a MIL or multiple lamps.…

C0035

Left Front Wheel Speed Sensor Circuit

Left front wheel speed sensor circuit. ABS and traction lights usually accompany this, and some cars also set engine codes related to speed.…

P0201

Injector Circuit / Open - Cylinder 1

Injector circuit fault on cylinder 1. Often pairs with a P0301 misfire.…

P0740

Torque Converter Clutch Circuit Malfunction

TCC circuit fault. You may notice higher RPM on the highway or shudder.…

P0741

Torque Converter Clutch Circuit Performance or Stuck Off

TCC is not applying as commanded. Highway RPM stays high and fuel economy drops.…

P0100

Mass or Volume Air Flow Circuit Malfunction

P0100 is an OBD2 diagnostic trouble code: Mass or Volume Air Flow Circuit Malfunction. Learn what it means, why the check engine light comes…

P0103

Mass or Volume Air Flow Circuit High Input

P0103 is an OBD2 diagnostic trouble code: Mass or Volume Air Flow Circuit High Input. Learn what it means, why the check engine light comes …

P0105

Manifold Absolute Pressure Circuit Malfunction

P0105 is an OBD2 diagnostic trouble code: Manifold Absolute Pressure Circuit Malfunction. Learn what it means, why the check engine light co…

P0106

MAP Circuit Range/Performance

P0106 is an OBD2 diagnostic trouble code: MAP Circuit Range/Performance. Learn what it means, why the check engine light comes on, and what …

P0107

MAP Circuit Low Input

P0107 is an OBD2 diagnostic trouble code: MAP Circuit Low Input. Learn what it means, why the check engine light comes on, and what to check…

P0108

MAP Circuit High Input

P0108 is an OBD2 diagnostic trouble code: MAP Circuit High Input. Learn what it means, why the check engine light comes on, and what to chec…

P0112

Intake Air Temperature Circuit Low

P0112 is an OBD2 diagnostic trouble code: Intake Air Temperature Circuit Low. Learn what it means, why the check engine light comes on, and …

P0116

Engine Coolant Temperature Circuit Range/Performance

P0116 is an OBD2 diagnostic trouble code: Engine Coolant Temperature Circuit Range/Performance. Learn what it means, why the check engine li…

P0117

Engine Coolant Temperature Circuit Low

P0117 is an OBD2 diagnostic trouble code: Engine Coolant Temperature Circuit Low. Learn what it means, why the check engine light comes on, …

P0121

Throttle Position Sensor A Circuit Range/Performance

P0121 is an OBD2 diagnostic trouble code: Throttle Position Sensor A Circuit Range/Performance. Learn what it means, why the check engine li…

P0123

Throttle Position Sensor A Circuit High

P0123 is an OBD2 diagnostic trouble code: Throttle Position Sensor A Circuit High. Learn what it means, why the check engine light comes on,…

P0125

Insufficient Coolant Temperature for Closed Loop

P0125 is an OBD2 diagnostic trouble code: Insufficient Coolant Temperature for Closed Loop. Learn what it means, why the check engine light …

P0130

O2 Sensor Circuit Malfunction (Bank 1 Sensor 1)

P0130 is an OBD2 diagnostic trouble code: O2 Sensor Circuit Malfunction (Bank 1 Sensor 1). Learn what it means, why the check engine light c…

P0131

O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)

P0131 is an OBD2 diagnostic trouble code: O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1). Learn what it means, why the check engine light c…

P0134

O2 Sensor Circuit No Activity (Bank 1 Sensor 1)

P0134 is an OBD2 diagnostic trouble code: O2 Sensor Circuit No Activity (Bank 1 Sensor 1). Learn what it means, why the check engine light c…

P0136

O2 Sensor Circuit Malfunction (Bank 1 Sensor 2)

P0136 is an OBD2 diagnostic trouble code: O2 Sensor Circuit Malfunction (Bank 1 Sensor 2). Learn what it means, why the check engine light c…

P0140

O2 Sensor Circuit No Activity (Bank 1 Sensor 2)

P0140 is an OBD2 diagnostic trouble code: O2 Sensor Circuit No Activity (Bank 1 Sensor 2). Learn what it means, why the check engine light c…

P0155

O2 Sensor Heater Circuit (Bank 2 Sensor 1)

P0155 is an OBD2 diagnostic trouble code: O2 Sensor Heater Circuit (Bank 2 Sensor 1). Learn what it means, why the check engine light comes …

P0161

O2 Sensor Heater Circuit (Bank 2 Sensor 2)

P0161 is an OBD2 diagnostic trouble code: O2 Sensor Heater Circuit (Bank 2 Sensor 2). Learn what it means, why the check engine light comes …

P0200

Injector Circuit Malfunction

P0200 is an OBD2 diagnostic trouble code: Injector Circuit Malfunction. Learn what it means, why the check engine light comes on, and what t…

P0202

Injector Circuit / Open - Cylinder 2

P0202 is an OBD2 diagnostic trouble code: Injector Circuit / Open - Cylinder 2. Learn what it means, why the check engine light comes on, an…

P0203

Injector Circuit / Open - Cylinder 3

P0203 is an OBD2 diagnostic trouble code: Injector Circuit / Open - Cylinder 3. Learn what it means, why the check engine light comes on, an…

P0204

Injector Circuit / Open - Cylinder 4

P0204 is an OBD2 diagnostic trouble code: Injector Circuit / Open - Cylinder 4. Learn what it means, why the check engine light comes on, an…

P0305

Cylinder 5 Misfire Detected

P0305 is an OBD2 diagnostic trouble code: Cylinder 5 Misfire Detected. Learn what it means, why the check engine light comes on, and what to…

P0306

Cylinder 6 Misfire Detected

P0306 is an OBD2 diagnostic trouble code: Cylinder 6 Misfire Detected. Learn what it means, why the check engine light comes on, and what to…

P0307

Cylinder 7 Misfire Detected

P0307 is an OBD2 diagnostic trouble code: Cylinder 7 Misfire Detected. Learn what it means, why the check engine light comes on, and what to…

P0308

Cylinder 8 Misfire Detected

P0308 is an OBD2 diagnostic trouble code: Cylinder 8 Misfire Detected. Learn what it means, why the check engine light comes on, and what to…

P0320

Ignition/Distributor Engine Speed Input Circuit

P0320 is an OBD2 diagnostic trouble code: Ignition/Distributor Engine Speed Input Circuit. Learn what it means, why the check engine light c…

P0330

Knock Sensor 2 Circuit Malfunction

P0330 is an OBD2 diagnostic trouble code: Knock Sensor 2 Circuit Malfunction. Learn what it means, why the check engine light comes on, and …

P0332

Knock Sensor 2 Circuit Low

P0332 is an OBD2 diagnostic trouble code: Knock Sensor 2 Circuit Low. Learn what it means, why the check engine light comes on, and what to …

P0336

Crankshaft Position Sensor A Circuit Range/Performance

P0336 is an OBD2 diagnostic trouble code: Crankshaft Position Sensor A Circuit Range/Performance. Learn what it means, why the check engine …

P0351

Ignition Coil A Primary/Secondary Circuit

P0351 is an OBD2 diagnostic trouble code: Ignition Coil A Primary/Secondary Circuit. Learn what it means, why the check engine light comes o…

P0400

EGR Flow Malfunction

P0400 is an OBD2 diagnostic trouble code: EGR Flow Malfunction. Learn what it means, why the check engine light comes on, and what to check …

P0403

EGR Circuit Malfunction

P0403 is an OBD2 diagnostic trouble code: EGR Circuit Malfunction. Learn what it means, why the check engine light comes on, and what to che…

P0404

EGR Circuit Range/Performance

P0404 is an OBD2 diagnostic trouble code: EGR Circuit Range/Performance. Learn what it means, why the check engine light comes on, and what …

P0410

Secondary Air Injection System Malfunction

P0410 is an OBD2 diagnostic trouble code: Secondary Air Injection System Malfunction. Learn what it means, why the check engine light comes …

P0441

EVAP Incorrect Purge Flow

P0441 is an OBD2 diagnostic trouble code: EVAP Incorrect Purge Flow. Learn what it means, why the check engine light comes on, and what to c…

P0446

EVAP Vent Control Circuit Malfunction

P0446 is an OBD2 diagnostic trouble code: EVAP Vent Control Circuit Malfunction. Learn what it means, why the check engine light comes on, a…

P0463

Fuel Level Sensor Circuit High

P0463 is an OBD2 diagnostic trouble code: Fuel Level Sensor Circuit High. Learn what it means, why the check engine light comes on, and what…

P0480

Cooling Fan 1 Control Circuit

P0480 is an OBD2 diagnostic trouble code: Cooling Fan 1 Control Circuit. Learn what it means, why the check engine light comes on, and what …

P0501

Vehicle Speed Sensor Range/Performance

P0501 is an OBD2 diagnostic trouble code: Vehicle Speed Sensor Range/Performance. Learn what it means, why the check engine light comes on, …

P0505

Idle Air Control System Malfunction

P0505 is an OBD2 diagnostic trouble code: Idle Air Control System Malfunction. Learn what it means, why the check engine light comes on, and…

P0562

System Voltage Low

P0562 is an OBD2 diagnostic trouble code: System Voltage Low. Learn what it means, why the check engine light comes on, and what to check ne…

P0601

Internal Control Module Memory Check Sum Error

P0601 is an OBD2 diagnostic trouble code: Internal Control Module Memory Check Sum Error. Learn what it means, why the check engine light co…

P0606

PCM Processor Fault

P0606 is an OBD2 diagnostic trouble code: PCM Processor Fault. Learn what it means, why the check engine light comes on, and what to check n…

P0705

Transmission Range Sensor Circuit Malfunction (PRNDL)

P0705 is an OBD2 diagnostic trouble code: Transmission Range Sensor Circuit Malfunction (PRNDL). Learn what it means, why the check engine l…

P0715

Input/Turbine Speed Sensor Circuit Malfunction

P0715 is an OBD2 diagnostic trouble code: Input/Turbine Speed Sensor Circuit Malfunction. Learn what it means, why the check engine light co…

P0720

Output Speed Sensor Circuit Malfunction

P0720 is an OBD2 diagnostic trouble code: Output Speed Sensor Circuit Malfunction. Learn what it means, why the check engine light comes on,…

P0730

Incorrect Gear Ratio

P0730 is an OBD2 diagnostic trouble code: Incorrect Gear Ratio. Learn what it means, why the check engine light comes on, and what to check …

P0750

Shift Solenoid A Malfunction

P0750 is an OBD2 diagnostic trouble code: Shift Solenoid A Malfunction. Learn what it means, why the check engine light comes on, and what t…

P0755

Shift Solenoid B Malfunction

P0755 is an OBD2 diagnostic trouble code: Shift Solenoid B Malfunction. Learn what it means, why the check engine light comes on, and what t…

B0000

Body Control Module Malfunction

B0000 is an OBD2 diagnostic trouble code: Body Control Module Malfunction. Learn what it means, why the check engine light comes on, and wha…

C0000

Chassis Control Module Malfunction

C0000 is an OBD2 diagnostic trouble code: Chassis Control Module Malfunction. Learn what it means, why the check engine light comes on, and …

U0001

High Speed CAN Communication Bus

U0001 is an OBD2 diagnostic trouble code: High Speed CAN Communication Bus. Learn what it means, why the check engine light comes on, and wh…

U0101

Lost Communication With TCM

U0101 is an OBD2 diagnostic trouble code: Lost Communication With TCM. Learn what it means, why the check engine light comes on, and what to…

OBD2 trouble code library