Understanding emission-related engine DTCs or diagnostic trouble codes is important because of two reasons. Firstly, your car’s current health can often be determined by everything that comes out of its exhaust pipe. The odor, the color, and the chemical components of its emission can often signify a particular problem that occurs in the car. Secondly, emission control is necessary to make sure that your car doesn’t violate the emission-related regulations.
The engine system of your car is connected to a computer, so in order to know fully what comes out of your car’s exhaust pipe, you only need to plug your OBD2 scanner into the data link connector to retrieve the emission-related engine DTCs. The codes will then tell you about what’s wrong with your car’s engine and other relevant components. The codes that you receive need to be interpreted. In order to interpret them, you need either a scanner that can interpret them or the format of DTCs that represent emission-related problems. Even if you have a scanner that can interpret the codes, it is recommended that you also know the format of emission-related engine DTCs.
Emission-Related Engine DTC Format
DTCs use the standard 5-character format. In order to understand which codes represent engine-related problems, you need to understand what each of the five characters means. The 5-character code basically consists of one letter followed by four numbers. The first letter signifies the location of the problem, with P for powertrain, B for body, C for chassis, and U for the network. The emission-related engine DTCs usually represent problems that occur in the powertrain, but emission-related problems may also be caused by faults in other systems, such as ABS and HVAC. For problems that are caused by non-powertrain components, the generation of the codes generally doesn’t trigger the turning on of the check engine light. Here we will focus only on emission-related problems that are signaled by powertrain codes (P).
The first number after the P letter determines the source of the codes, which is either generic and global if it is 0 or manufacturer-specific if it is 1. Generic codes may as well start with P2 and P34 to P39; however, emission-related engine DTCs generally start with P0, especially because engine-related problems are hardly represented by manufacturer-specific codes.
The second number (or the third character) in the code represents the subsystem where the problem occurs. It can be 1 for fuel and air metering, 2 for the same metering in the injector circuit, 3 for ignition system or misfire, 4 for auxiliary emission controls, 5 for vehicle speed control and idle control system, 6 for computer circuit, and 7 and 8 for transmission. This number is considered important because it specifically guides you to the exact location of the problem. Although you haven’t known the nature of the problem, being able to pinpoint its location is considered a big step.
To understand the specific nature of the problem, you need to refer to the last two numbers. There is a big database that lists all engine and transmission problems by specifically referring to these two numbers. You can either keep the database or use a scan tool that can read and interpret emission-related engine DTCs.
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