The modern vehicle is a complex machine, but thankfully, onboard diagnostics systems are here to simplify troubleshooting. The On-Board Diagnostics II (OBD2) system is a standardized system in most cars and light trucks manufactured after 1996, designed to monitor various vehicle systems. When something goes wrong, the vehicle’s computer, known as the Engine Control Unit (ECU), logs a Diagnostic Trouble Code (DTC). These codes can be easily accessed using an Obd2 Code Reader Codes device, empowering car owners and mechanics to quickly identify potential issues.
Understanding these obd2 code reader codes is the first step towards effective car maintenance and repair. By plugging a scanner into your car’s OBD2 port, typically located under the dashboard, you can retrieve these stored codes and begin to diagnose the problem. But how do you decipher these codes? Let’s break down the structure of OBD2 DTCs.
Understanding the Structure of OBD2 Codes
OBD2 codes are not random numbers and letters; they follow a specific format, making it easier to understand the general area of the problem even before consulting a detailed chart. Each code is composed of five characters: a letter followed by four numbers.
1. The First Letter: Category of the Fault
The first letter of the DTC indicates the primary system affected by the fault:
- P (Powertrain): Relates to the engine, transmission, and associated drivetrain components. This is the most common category of OBD2 codes.
- B (Body): Concerns body-related systems like airbags, power windows, electronic seats, and central locking.
- C (Chassis): Deals with chassis systems such as braking, suspension, and steering.
- U (Network): Indicates network and vehicle integration issues, often related to the communication systems within the car, like the CAN bus.
2. The First Number: Code Type
The first number following the letter specifies whether the code is a standardized SAE code or a manufacturer-specific code:
- 0: Indicates a standardized or generic OBD2 code. These codes are the same across all makes and models of vehicles that comply with OBD2 standards.
- 1: Signifies a manufacturer-specific code. These codes are defined by the car manufacturer and may have a more specific meaning related to a particular vehicle make or model.
- 2 & 3: These are reserved for manufacturer-specific codes as well, representing enhanced or more detailed diagnostics beyond the standard OBD2 requirements.
3. The Second Number: Subsystem Affected
The second number pinpoints the specific subsystem within the broader category identified by the first letter. For Powertrain (P) codes, the common subsystems are:
- 0: Fuel and Air Metering and Auxiliary Emission Controls
- 1: Fuel and Air Metering
- 2: Fuel and Air Metering (Injector Circuit)
- 3: Ignition Systems or Misfires
- 4: Auxiliary Emission Controls
- 5: Vehicle Speed Control & Idle Control Systems
- 6: Computer & Output Circuit
- 7: Transmission (For P07xx codes, P27xx codes, and P37xx codes)
4. The Third and Fourth Numbers: Specific Fault
The last two digits provide a precise identification of the particular fault within the subsystem. These numbers are sequential and further detail the nature of the problem. For example, in a P03xx code, ’01’ to ’08’ typically indicate misfires in cylinders 1 through 8, respectively.
Example: Decoding P0303
Let’s take the example code P0303 to illustrate how to interpret obd2 code reader codes:
- P: Powertrain (Engine or Transmission related)
- 0: Standardized SAE code
- 3: Ignition system or misfire issue
- 03: Specific fault – Misfire detected in cylinder 3
Therefore, P0303 indicates a Powertrain related, standardized code pointing to an ignition system problem, specifically a misfire in cylinder number 3.
What are… Diagnostic Trouble Codes
Understanding Diagnostic Trouble Codes with OBD2 scanner.
Common OBD2 Trouble Codes Chart
While understanding the structure is helpful, a comprehensive OBD2 trouble code chart is essential for accurate diagnosis. Here is a list of some common OBD2 codes and their descriptions:
| Code | Code Identification |
|---|---|
| P0101 | Mass air flow (MAF) sensor circuit, range or performance problem |
| P0102 | Mass air flow (MAF) sensor circuit, low input |
| P0103 | Mass air flow (MAF) sensor circuit, high input |
| P0106 | Manifold absolute pressure (MAP) sensor circuit, range or performance problem |
| P0107 | Manifold absolute pressure (MAP) sensor circuit, low input |
| P0108 | Manifold absolute pressure (MAP) sensor circuit, high input |
| P0112 | Intake air temperature (IAT) circuit, low input |
| P0113 | Intake air temperature (IAT) circuit, high input |
| P0117 | Engine coolant temperature (ECT) circuit, low input |
| P0118 | Engine coolant temperature (ECT) circuit, high input |
| P0121 | Throttle position sensor (TPS) circuit, range or performance problem |
| P0122 | Throttle position sensor (TPS) circuit, low input |
| P0123 | Throttle position sensor (TPS) circuit, high input |
| P0125 | Insufficient coolant temperature for closed loop fuel control |
| P0131 | Oxygen sensor circuit, low voltage (pre-converter sensor, left bank) |
| P0132 | Oxygen sensor circuit, high voltage (pre-converter sensor, left bank) |
| P0133 | Oxygen sensor circuit, slow response (pre-converter sensor, left bank) |
| P0134 | Oxygen sensor circuit – no activity detected (pre-converter sensor, left bank) |
| P0135 | Oxygen sensor heater circuit malfunction (pre-converter sensor, left bank) |
| P0137 | Oxygen sensor circuit, low voltage (post-converter sensor, left bank) |
| P0138 | Oxygen sensor circuit, high voltage (post-converter sensor, left bank) |
| P0140 | Oxygen sensor circuit – no activity detected (post-converter sensor, left bank) |
| P0141 | Oxygen sensor heater circuit malfunction (post-converter sensor, left bank) |
| P0143 | Oxygen sensor circuit, low voltage (#2 post-converter sensor, left bank) |
| P0144 | Oxygen sensor circuit, high voltage (#2 post-converter sensor, left bank) |
| P0146 | Oxygen sensor circuit – no activity detected (#2 post-converter sensor, left bank) |
| P0147 | Oxygen sensor heater circuit malfunction (#2 post-converter sensor, left bank) |
| P0151 | Oxygen sensor circuit, low voltage (pre-converter sensor, right bank) |
| P0152 | Oxygen sensor circuit, high voltage (pre-converter sensor, right bank) |
| P0153 | Oxygen sensor circuit, slow response (pre-converter sensor, right bank) |
| P0154 | Oxygen sensor circuit – no activity detected (pre-converter sensor, right bank) |
| P0155 | Oxygen sensor heater circuit malfunction (pre-converter sensor, right bank) |
| P0157 | Oxygen sensor circuit, low voltage (post-converter sensor, right bank) |
| P0158 | Oxygen sensor circuit, high voltage (post-converter sensor, right bank) |
| P0160 | Oxygen sensor circuit – no activity detected (post-converter sensor, right bank) |
| P0161 | Oxygen sensor heater circuit malfunction (post-converter sensor, right bank) |
| P0171 | System too lean, left bank |
| P0172 | System too rich, left bank |
| P0174 | System too lean, right bank |
| P0175 | System too rich, right bank |
| P0300 | Engine misfire detected |
| P0301 | Cylinder number 1 misfire detected |
| P0302 | Cylinder number 2 misfire detected |
| P0303 | Cylinder number 3 misfire detected |
| P0304 | Cylinder number 4 misfire detected |
| P0305 | Cylinder number 5 misfire detected |
| P0306 | Cylinder number 6 misfire detected |
| P0307 | Cylinder number 7 misfire detected |
| P0308 | Cylinder number 8 misfire detected |
| P0325 | Knock sensor circuit malfunction |
| P0327 | Knock sensor circuit, low output |
| P0336 | Crankshaft position sensor circuit, range or performance problem |
| P0337 | Crankshaft position sensor, low output |
| P0338 | Crankshaft position sensor, high output |
| P0339 | Crankshaft position sensor, circuit intermittent |
| P0340 | Camshaft position sensor circuit |
| P0341 | Camshaft position sensor circuit, range or performance problem |
| P0401 | Exhaust gas recirculation, insufficient flow detected |
| P0404 | Exhaust gas recirculation circuit, range or performance problem |
| P0405 | Exhaust gas recirculation sensor circuit low |
| P0410 | Secondary air injection system |
| P0418 | Secondary air injection pump relay control circuit |
| P0420 | Catalyst system efficiency below threshold, left bank |
| P0430 | Catalyst system efficiency below threshold, right bank |
| P0440 | Evaporative emission control system malfunction |
| P0441 | Evaporative emission control system, purge control circuit malfunction |
| P0442 | Evaporative emission control system, small leak detected |
| P0446 | Evaporative emission control system, vent system performance |
| P0452 | Evaporative emission control system, pressure sensor low input |
| P0453 | Evaporative emission control system, pressure sensor high input |
| P0461 | Fuel level sensor circuit, range or performance problem |
| P0462 | Fuel level sensor circuit, low input |
| P0463 | Fuel level sensor circuit, high input |
| P0500 | Vehicle speed sensor circuit |
| P0506 | Idle control system, rpm lower than expected |
| P0507 | Idle control system, rpm higher than expected |
| P0601 | Powertrain Control Module, memory error |
| P0602 | Powertrain Control module, programming error |
| P0603 | Powertrain Control Module, memory reset error |
| P0604 | Powertrain Control Module, memory error (RAM) |
| P0605 | Powertrain Control Module, memory error (ROM) |
* Note: Not all codes are applicable to every vehicle model. Always refer to your vehicle’s specific repair manual for detailed diagnostic procedures and code interpretations.
Conclusion
Understanding obd2 code reader codes empowers you to take a proactive approach to vehicle maintenance. While an obd2 code reader codes tool provides the initial clue, remember that it is just the starting point of the diagnostic process. Always consult repair manuals and seek professional advice when needed to ensure accurate diagnosis and repair of your vehicle. By learning to interpret these codes, you are taking a significant step towards becoming a more informed and capable car owner.
