The Diagnostic Trouble Codes Guide

What are Diagnostic Trouble Codes

Diagnostic Trouble Codes (DTC) are five-digit codes, made of letters and numbers, that provides reasoning for vehicle issues and malfunctions. This system was created by the Society of Automotive Engineers for automakers to comply with vehicle emission regulations.

How to read a DTC

The codes are triggered by the onboard diagnostics (OBD) system (OBD-II, J1939) in vehicles when an initial issue is detected. Depending on the specific issue, this could appear in the form of a check engine light on the vehicle’s dashboard. To find out what the issue may be, these codes can be read via a scanner that is plugged into the vehicle’s designated port. The location of this port can be found in the vehicle’s manufacturer guide.

Initially, DTCs can be confusing to decipher or to readily pinpoint the issue. Here’s a guide to help you understand each code:

  • The first character is a letter that defines which control system is having the issue.
    • P – signals a powertrain issue which consists of the engine, transmission, fuel system, and affiliated accessories
    • C – is for chassis, and refers to the mechanical system outside of the passenger compartment such as the steering, suspension, and brakes
    • B – stands for body and refer to parts that are found in the passenger compartment area
    • U – indicates a network issue. This letter indicates that there are issues related to the vehicle’s onboard computer and related systems
  • The second character is a number, usually 0-2, that indicates if the code is standardized.
    • 0 – generic
    • 1 – vehicle manufacturer specific
    • 2 – rare and is dependent on the previous letter (P,C,B,U)
  • The third character is a number, 1-8, referring to the following issues:
    • 1 – fuel or air metering system
    • 2 – fuel or air metering injection system
    • 3 – ignition system
    • 4 – emissions system
    • 5 – vehicle speed controls or idle control system
    • 6 – computer output circuit
    • 7 or 8 – transmission
  • The fourth and fifth characters are two numbers between 0-99 that are known as specific fault indexes. To pinpoint this issue, refer to the vehicle’s manufacturer manual for further explanation.

Common Diagnostic Trouble Codes

Vehicle issues can be unique but at times, can have similar code readings. Here’s a list of common codes and their meaning:

P0101: Mass Air Flow (MAF) circuit or sensor fault
P0110: An intake air temperature sensor circuit malfunction
P0120: Throttle pedal position sensor or switch A circuit malfunction
P0130: O2 sensor (oxygen sensor) circuit malfunction (Bank 1, Sensor 1)
P0141: O2 sensor (oxygen sensor) heater circuit malfunction (Bank 1, Sensor 2)
P0215: Engine shutoff solenoid malfunction
P0300: Random or multiple cylinders misfire detected
P0352: Ignition coil B primary or secondary circuit malfunction
P0353: Ignition coil C primary or secondary circuit malfunction
P0442: A small system leak within the vehicle’s evaporative emission control system
P0500: A malfunction in the vehicle’s speed sensor
P0606: A PCM (or ECM) powertrain malfunction
P0650: Malfunction Indicator Lamp (check engine light) control circuit malfunction
P0654: Engine RPM (revolution/rotations per minute) output circuit malfunction
P0656: Fuel level output circuit malfunction
P0706: A transmission range sensor circuit range fault
P1108: Dual alternator battery lamp circuit malfunction
P1794: Battery voltage circuit malfunction
B1203: Fuel sender circuit short to battery
B1927: Faulty passenger side airbag

Diagnostic Trouble Codes and Telematics

A good benefit of having a telematics system integrated into fleet management software is that it helps track DTCs within their fleet. Through the telematics system, fleet managers can receive indications if there are problems with the vehicle.

Frequently Asked Questions

What does OBD-II or J1939 compliant mean?

OBD-II is within cars and trucks that are built after January 1st, 1996 and J1939 are within diesel engine vehicles such as heavy-duty trucks and buses

How do I know if my vehicle is OBD-II or J1939 compliant?

You can check the vehicle’s owner manual or the manufacturers website to confirm capability

What causes DTCs?

Your vehicle’s OBD system, OBD-II or J1939, will identify if there is an issue or malfunction and a specific DTC will be generated via scanner

How are DTCs cleared?

To ensure the codes are cleared, all issues relating to the codes must be fixed

Are DTCs universal?

Mostly, but there are instances where the codes are manufacturer specific. A way to figure this out is by identifying the second digit within the code. A 0 will indicate a universal code and a 1 will indicate it being manufacturer specific

What’s Next?

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