OBD2 Trouble Codes Guide

Complete database of diagnostic trouble codes with meanings, causes, and solutions

Code Categories

  • P - Powertrain
  • B - Body
  • C - Chassis
  • U - Network

Code Structure

P
0
4
2
0

1st: Category

2nd: Code Type (0=Standard, 1=Manufacturer)

3rd: System

4th & 5th: Specific Fault

Common Systems

  • 1,2 - Fuel and Air Metering
  • 3 - Ignition Systems
  • 4 - Auxiliary Emissions
  • 5 - Vehicle Speed/Idle Control
  • 6 - Computer/Output Circuits
  • 7,8,9 - Transmission

Severity Levels

  • Critical - Immediate attention required
  • Medium - Schedule service soon
  • Low - Monitor and maintain

Filters

P0300

Random/Multiple Cylinder Misfire Detected

High

Common Symptoms

  • Check Engine Light flashing
  • Engine running rough
  • Vibration while driving
  • Loss of power
  • Poor fuel economy

Common Causes

  • Faulty spark plugs
  • Bad ignition coils
  • Fuel injector problems
  • Vacuum leak
  • Low fuel pressure
  • Poor compression

Possible Fixes

  • Replace spark plugs
  • Test and replace ignition coils
  • Clean or replace fuel injectors
  • Repair vacuum leaks
  • Check fuel pressure
  • Perform compression test
Category: Powertrain
System: Engine

P0420

Catalyst System Efficiency Below Threshold (Bank 1)

Medium

Common Symptoms

  • Check Engine Light
  • Failed emissions test
  • Poor fuel economy
  • Loss of power at high speeds

Common Causes

  • Failed catalytic converter
  • Exhaust leak
  • O2 sensor malfunction
  • Rich/lean fuel condition
  • Engine misfire

Possible Fixes

  • Replace catalytic converter
  • Repair exhaust leaks
  • Replace O2 sensors
  • Check fuel system
  • Address underlying engine issues
Category: Powertrain
System: Emissions

P0171

System Too Lean (Bank 1)

Medium

Common Symptoms

  • Check Engine Light
  • Rough idle
  • Poor acceleration
  • Engine hesitation
  • Poor fuel economy

Common Causes

  • Vacuum leak
  • Mass air flow sensor issues
  • Fuel pressure problems
  • Dirty fuel injectors
  • Faulty oxygen sensors
  • PCV valve issues

Possible Fixes

  • Fix vacuum leaks
  • Clean/replace MAF sensor
  • Check fuel pressure
  • Clean fuel injectors
  • Replace oxygen sensors
  • Replace PCV valve
Category: Powertrain
System: Fuel

P0700

Transmission Control System Malfunction

High

Common Symptoms

  • Check Engine Light
  • Transmission warning light
  • Shifting problems
  • Slipping transmission
  • Delayed engagement

Common Causes

  • Transmission control module failure
  • Wiring issues
  • Solenoid problems
  • Low transmission fluid
  • Internal transmission damage

Possible Fixes

  • Diagnose transmission control module
  • Repair wiring
  • Replace solenoids
  • Check/replace transmission fluid
  • Transmission rebuild/replacement
Category: Powertrain
System: Transmission

P0102

Mass Air Flow Circuit Low Input

Medium

Common Symptoms

  • Check Engine Light
  • Poor idle
  • Hesitation during acceleration
  • Stalling
  • Poor fuel economy

Common Causes

  • Dirty MAF sensor
  • Failed MAF sensor
  • Wiring problems
  • Air intake leaks
  • Contaminated connector

Possible Fixes

  • Clean MAF sensor
  • Replace MAF sensor
  • Repair wiring
  • Fix air intake leaks
  • Clean/repair connector
Category: Powertrain
System: Sensors

P0351

Ignition Coil A Primary/Secondary Circuit Malfunction

High

Common Symptoms

  • Check Engine Light
  • Engine misfire
  • Rough idle
  • Poor acceleration
  • Increased fuel consumption

Common Causes

  • Failed ignition coil
  • Broken wiring
  • Bad spark plug
  • ECU problems
  • Corroded connections

Possible Fixes

  • Replace ignition coil
  • Repair wiring
  • Replace spark plugs
  • Check ECU
  • Clean/repair connections
Category: Powertrain
System: Ignition

B1000

Driver Side Airbag Circuit Malfunction

Critical

Common Symptoms

  • Airbag warning light
  • SRS system warning
  • Airbag system disabled

Common Causes

  • Clock spring failure
  • Wiring harness issues
  • Airbag module failure
  • Impact sensor malfunction
  • Control module issues

Possible Fixes

  • Replace clock spring
  • Repair wiring harness
  • Replace airbag module
  • Replace impact sensors
  • Reset/replace control module
Category: Body
System: Safety

C0040

Brake Pressure Sensor Circuit Malfunction

High

Common Symptoms

  • ABS warning light
  • Brake warning light
  • ABS system disabled
  • Hard brake pedal
  • Poor braking performance

Common Causes

  • Failed brake pressure sensor
  • Wiring issues
  • ABS module failure
  • Hydraulic system problems
  • Control module issues

Possible Fixes

  • Replace brake pressure sensor
  • Repair wiring
  • Replace ABS module
  • Repair hydraulic system
  • Reset/replace control module
Category: Chassis
System: Brakes

U0101

Lost Communication with TCM

High

Common Symptoms

  • Check Engine Light
  • Transmission issues
  • Vehicle in limp mode
  • Erratic shifting
  • Limited functionality

Common Causes

  • CAN bus system failure
  • TCM failure
  • Wiring problems
  • Power supply issues
  • Ground connection problems

Possible Fixes

  • Diagnose CAN bus system
  • Replace TCM
  • Repair wiring
  • Check/repair power supply
  • Clean/repair ground connections
Category: Network
System: Communication

P0455

Evaporative Emission System Leak Detected (Gross Leak)

Medium

Common Symptoms

  • Check Engine Light
  • Fuel smell
  • Failed emissions test
  • Poor fuel economy

Common Causes

  • Loose/damaged gas cap
  • EVAP hose leak
  • Purge valve failure
  • Charcoal canister damage
  • Fuel tank leak

Possible Fixes

  • Replace gas cap
  • Replace EVAP hoses
  • Replace purge valve
  • Replace charcoal canister
  • Repair/replace fuel tank
Category: Powertrain
System: EVAP

P0201

Injector Circuit Malfunction - Cylinder 1

High

Common Symptoms

  • Check Engine Light
  • Rough idle
  • Misfiring
  • Poor acceleration
  • Increased fuel consumption
  • Hard starting

Common Causes

  • Failed fuel injector
  • Wiring harness issues
  • PCM failure
  • Short circuit
  • Clogged injector

Possible Fixes

  • Replace fuel injector
  • Repair wiring harness
  • Clean fuel injectors
  • Check PCM
  • Test fuel pressure
Category: Powertrain
System: Fuel

P0131

O2 Sensor Circuit Low Voltage (Bank 1, Sensor 1)

Medium

Common Symptoms

  • Check Engine Light
  • Poor fuel economy
  • Rough idle
  • Failed emissions test
  • Black exhaust smoke

Common Causes

  • Failed O2 sensor
  • Wiring issues
  • Exhaust leak
  • Contaminated sensor
  • Short circuit

Possible Fixes

  • Replace O2 sensor
  • Repair wiring
  • Fix exhaust leaks
  • Clean sensor connections
  • Check ground circuit
Category: Powertrain
System: Emissions

P0016

Crankshaft Position - Camshaft Position Correlation (Bank 1 Sensor A)

High

Common Symptoms

  • Check Engine Light
  • Engine stalling
  • Rough running
  • Poor performance
  • Hard starting
  • Increased emissions

Common Causes

  • Timing chain stretched
  • Variable valve timing issues
  • Camshaft sensor failure
  • Crankshaft sensor failure
  • Timing chain guide wear

Possible Fixes

  • Replace timing chain
  • Replace VVT solenoid
  • Replace cam/crank sensors
  • Update PCM software
  • Replace timing guides
Category: Powertrain
System: Engine

P0299

Turbocharger/Supercharger Underboost Condition

High

Common Symptoms

  • Check Engine Light
  • Loss of power
  • Slow acceleration
  • Whistling noise
  • Limp mode activation

Common Causes

  • Boost leak
  • Wastegate malfunction
  • Turbo failure
  • Intake restrictions
  • Faulty boost sensor

Possible Fixes

  • Repair boost leaks
  • Replace wastegate
  • Rebuild/replace turbo
  • Clean intake system
  • Replace boost sensor
Category: Powertrain
System: Forced Induction

P0A80

Replace Hybrid Battery Pack

Critical

Common Symptoms

  • Check Engine Light
  • Hybrid system warning
  • Poor fuel economy
  • Reduced power
  • Battery charge issues

Common Causes

  • Aged battery pack
  • Failed battery cells
  • Battery management system issue
  • Cooling system problems
  • Voltage sensor issues

Possible Fixes

  • Replace hybrid battery
  • Replace individual cells
  • Repair cooling system
  • Update BMS software
  • Clean battery connections
Category: Powertrain
System: Hybrid

C0035

Left Front Wheel Speed Sensor Circuit

High

Common Symptoms

  • ABS Light on
  • Traction control disabled
  • Stability control disabled
  • Pulsating brake pedal
  • Poor braking performance

Common Causes

  • Failed speed sensor
  • Damaged wiring
  • Dirty sensor
  • Damaged tone ring
  • Corroded connections

Possible Fixes

  • Replace wheel speed sensor
  • Repair wiring
  • Clean sensor/tone ring
  • Replace hub assembly
  • Repair connections
Category: Chassis
System: ABS

P0733

Gear 3 Incorrect Ratio

High

Common Symptoms

  • Check Engine Light
  • Transmission slipping
  • Harsh shifting
  • No 3rd gear
  • Limp mode activation

Common Causes

  • Worn clutch pack
  • Solenoid failure
  • Low transmission fluid
  • Internal wear
  • Valve body issues

Possible Fixes

  • Replace clutch pack
  • Replace solenoid
  • Service transmission
  • Rebuild transmission
  • Replace valve body
Category: Powertrain
System: Transmission

P0011

Intake Camshaft Position Timing - Over Advanced (Bank 1)

Medium

Common Symptoms

  • Check Engine Light
  • Poor idle
  • Reduced power
  • Poor fuel economy
  • Rattling noise

Common Causes

  • VVT solenoid failure
  • Oil control valve clogged
  • Low oil pressure
  • Stretched timing chain
  • Dirty engine oil

Possible Fixes

  • Replace VVT solenoid
  • Clean oil control valve
  • Check oil pressure
  • Replace timing chain
  • Oil change with flush
Category: Powertrain
System: Engine

P0089

Fuel Pressure Regulator Performance

High

Common Symptoms

  • Check Engine Light
  • Hard starting
  • Rough idle
  • Loss of power
  • Engine stalling

Common Causes

  • Failed fuel pressure regulator
  • Fuel pump issues
  • Clogged fuel filter
  • Wiring problems
  • PCM issues

Possible Fixes

  • Replace pressure regulator
  • Replace fuel pump
  • Replace fuel filter
  • Repair wiring
  • Update PCM software
Category: Powertrain
System: Fuel

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