TORQDEX // OBD-II REFERENCE

OBD-II Trouble Codes

Look up a diagnostic trouble code, understand what system triggered it, and work through the fault logically before replacing parts.

CODE LOOKUP

Enter a five-character OBD-II code.

01 // READ THE CODE

What the first letter means

The first character identifies the general system where the diagnostic trouble code originated.

P

Powertrain

Engine, transmission, fuel, ignition, emissions, and related powertrain systems.

B

Body

Body electronics, climate systems, restraint systems, seats, lighting, and related control modules.

C

Chassis

ABS, steering, suspension, braking, and other chassis-related systems.

U

Network

Communication faults between control modules and vehicle data networks.

02 // CODE STRUCTURE

Breaking down a trouble code

P 0 3 0 0
P System

Powertrain

0 Code Type

Generic / SAE

3 Subsystem

Ignition / Misfire

00 Specific Fault

Random / multiple misfire

03 // COMMON POWERTRAIN CODES

Popular code lookups

Start with some of the most commonly encountered powertrain trouble codes.

P0300

Random / Multiple Cylinder Misfire

Misfires have been detected across multiple cylinders or without one specific cylinder identified.

VIEW CODE → P0301

Cylinder 1 Misfire Detected

The engine control module has detected repeated misfires associated with cylinder 1.

VIEW CODE → P0171

System Too Lean — Bank 1

Fuel-trim correction indicates that Bank 1 is operating lean beyond the expected range.

VIEW CODE → P0172

System Too Rich — Bank 1

Fuel-trim correction indicates an excessively rich operating condition on Bank 1.

VIEW CODE → P0420

Catalyst Efficiency Below Threshold

Catalyst monitoring indicates that Bank 1 catalytic-converter efficiency is below threshold.

VIEW CODE → P0442

Small EVAP Leak Detected

The evaporative emissions system has detected a leak within the small-leak range.

VIEW CODE → P0455

Large EVAP Leak Detected

The EVAP system cannot maintain the expected pressure or vacuum during its leak test.

VIEW CODE → P0562

System Voltage Low

Vehicle system voltage has fallen below the expected operating range.

VIEW CODE → P0101

Mass Air Flow Range / Performance

MAF sensor readings are outside the expected operating range for current engine conditions.

VIEW CODE → P0128

Coolant Temperature Below Thermostat Regulation

Engine coolant temperature is not reaching the expected operating temperature quickly enough.

VIEW CODE →

TORQDEX // DIAGNOSTIC PRINCIPLE

A code points to a problem. It does not condemn a part.

Diagnostic trouble codes report conditions detected by vehicle control modules. Wiring faults, vacuum leaks, mechanical failures, sensor problems, low system voltage, and other causes can produce similar codes. Confirm the fault with testing before replacing components.