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How Can Autel Scanners Help You Understand DTC Codes?
If you are new to the automotive diagnostics industry, you must be very curious about DTC codes. When you use an OBD II code reader or OBD II scanner, you will always see some English and numeric codes, which may make you confused. Do you know what they mean?
Fortunately, most Autel scanners already have explanations of the meaning of DTC codes, which can help you better solve the diagnosed problems. However, I believe that some novices may still be confused by some explanations. After all, some professional terms are always obscure and difficult to understand.
Today, we'll take you deeper into DTC codes from multiple perspectives: what the different codes mean, how to read and understand them with an Autel scanner, and how to perform inspections and repairs when common fault codes appear. Let's learn together!
DTC codes are closely related to cars.
Concept Explanation
What is a DTC Code?
Many car owners have experienced this: the "check engine light" on the dashboard suddenly illuminates while driving, even though the vehicle continues to operate normally. This often leads to confusion: What went wrong? Is repair necessary immediately?
This brings us to the topic of DTC codes.
A DTC (Diagnostic Trouble Code) is a combination of letters and numbers stored by the vehicle's onboard diagnostics system (OBD-II) when a fault is detected. It acts like a "health language" for the vehicle, helping the owner or repair technician quickly identify the problem.
Simply put: a DTC code is a combination of a warning signal and a problem indicator.
What is DTC in a Car?
In modern cars, DTCs are a crucial component of the OBD-II system. The OBD-II interface is standard on nearly all models after 1996, and any fault information is recorded in the vehicle's ECU (Engine Control Unit) as a DTC.
This means:
- Car owners can quickly identify basic vehicle problems using a scanner.
- Technicians can then use more specialized diagnostic tools to further confirm and repair the problem.
In short, DTCs are the vehicle's self-diagnosis.
Read the DTC code in the car ECU through the OBD port.
How do you interpret DTC codes?
DTC Code Meaning
The DTC code has five characters. Each character corresponds to a specific problem with your vehicle. Below is an overview of what each character means.
First DTC Character
The first DTC character is always a letter. There are four types of codes:
- P Code: "P" indicates a problem with the powertrain. This includes the engine, transmission, drivetrain, and fuel system.
- C Code: "C" indicates a problem with the chassis. This refers to mechanical systems outside the passenger compartment, such as the steering, suspension, and brakes.
- B Code: "B" indicates a problem with the body. This covers components located in the passenger compartment.
- U Code: "U" indicates a problem with the vehicle's onboard computer and the integrated functions managed by OBD.
Second DTC Character
The second DTC character is a number and can be either "0" or "1":
- 0: "0" indicates a standard SAE International code. It is also called a universal code, meaning it applies to all vehicles that follow the OBD-II International standard.
- 1: "1" represents a code specific to the vehicle make or model. This is called an enhanced code, meaning it doesn't meet SAE standards. If you see a "1," contact the vehicle manufacturer directly for more information.
The five characters of the DTC code have different meanings.
Third DTC Character
If the second DTC character is "0," the third character helps you determine which subsystem is malfunctioning. There are eight digits:
- 0: Fuel and air metering and auxiliary emission controls
- 1: Fuel and air metering injection system
- 2: Fuel and air metering (injection system)
- 3: Ignition system or misfire
- 4: Auxiliary emission controls
- 5: Vehicle speed control, idle control system, and auxiliary inputs
- 6: Computer output circuits
- 7-8: Transmission
Fourth and Fifth DTC Characters
The fourth and fifth DTC codes are two-digit numbers from 0 to 99 called the "Specific Fault Index." They identify the specific malfunction in your vehicle.
Example: DTC code P0420
You have an OBD II scanner and plug it into your vehicle's diagnostic port. It then displays DTC code P0420, but what does it actually mean?
Here's what this common code means:
- P: The letter "P" indicates a problem with the vehicle's powertrain or fuel system.
- 0: The number "0" applies to all OBD-II-compliant vehicles (1996 and newer).
- 4: The number "4" indicates a malfunction with one of the auxiliary emission control devices.
- 20: The number "20" indicates a problem with the vehicle's catalytic converter.
Vehicles displaying the P0420 trouble code have a problem with their catalytic converter. Oxygen levels are below expected thresholds, and the system is leaking more pollutants into the air—definitely a problem you should address as soon as possible.
If you are interested in this fault code or have detected this fault code through the auto diagnostic tool but don't know how to deal with it, you can refer to the solution in the link below:
Common DTC Code Examples
The following is a list of some DTC codes that are commonly encountered in car maintenance:
| DTC Codes | Meaning |
| P0171 | Lean Fuel Mixture (commonly caused by an oxygen sensor or intake system abnormality) |
| P0300 | Random/Multiple Cylinder Ignition Misfire |
| P0420 | Inefficient Three-Way Catalyst (usually related to the emissions system) |
| P0446 | EVAP System Ventilation Valve Circuit Malfunction |
| C0035 | Left Front Wheel Speed Sensor Circuit Malfunction |
| U0100 | Loss of Communication with the ECU |
| P0700 | Transmission control system malfunction |
| P0174 | Engine is running too lean on Bank 2 |
Among these, P0171 and P0420 are the most typical and frequently searched for by vehicle owners.
DTC Code P0171: Indicates a lean fuel mixture. Common causes include an intake system leak, insufficient fuel pump pressure, or a damaged oxygen sensor.
DTC Code P0420: Indicates decreased three-way catalytic converter efficiency. This may be caused by incomplete engine combustion, a faulty oxygen sensor, or damage to the three-way catalytic converter itself.
How to Read DTC Codes?
To retrieve fault codes, you need an OBD-II diagnostic tool. This is where the Autel scanner comes in.
Reading Process:
- Find your car's OBD-II port (usually near the driver's side footrest).
- Plug the Autel scanner into the port and turn on the ignition.
- The scanner will communicate with the vehicle's ECU and display the fault code after a few seconds.
- The scanner not only displays the code but also explains its meaning, eliminating the need for a lookup table.
DTC Codes can be detected using Autel scanner.
Advantages of Autel Scanners
Why is the Autel scanner recommended for reading and understanding DTC codes? The following are the main reasons:
- Full-system diagnostics: Not only the engine, but also the ABS, SRS airbags, transmission, and body modules.
- Real-time data streaming: While reading DTCs, you can view sensor data streams to determine whether the fault is real or incidental.
- Bidirectional control: High-end models support bidirectional control, actively triggering components such as the fan and fuel pump to confirm the cause of the fault.
- Rich service functions: Including oil light reset, brake system bleeding, throttle calibration, TPMS tire pressure monitoring reset, and more.
- User-friendly: Autel devices often have built-in fault code explanations, making them easy to understand even for DIY car owners.
Recommended Models
- Autel MaxiCOM MK900BT: Ideal for DIY car owners, supports over 40 service functions, and can quickly read and clear fault codes.
- Autel MaxiSys Ultra S2: Preferred by professional technicians, supports ECU programming and in-depth diagnostics, and offers comprehensive functionality.
Summary
DTC codes are the core of vehicle self-diagnosis. Understanding DTC codes and a list of common DTC codes, especially high-frequency codes like P0171 and P0420, can help drivers quickly understand their vehicle's condition.
With the Autel scanner, both DIY car owners and professional technicians can quickly read, interpret, and resolve DTCs, significantly improving repair efficiency and avoiding unnecessary costs.
If you're looking for a tool that meets everyday needs while also providing professional functionality, the Autel scanner is a worthwhile investment.