Ultimate Guide to Chevrolet OBD-II Trouble Codes & Diagnostic Help

When your Chevrolet’s “check engine” light comes on, it’s not just a vague warning – it’s a signal that your vehicle is trying to tell you something specific. That’s where Chevrolet OBD-II codes come in. These alphanumeric codes pinpoint the exact problem, whether it’s an engine, transmission, or emissions issue. But what do they mean, and how do you decipher them?

You’ll need a scan tool or code reader to retrieve the codes, but that’s just the first step. Can you afford to ignore the warning signs, or do you want to get to the bottom of what’s going on under the hood?

Understanding OBD-II Codes

When troubleshooting issues with your Chevrolet, understanding OBD-II codes is crucial to identifying and resolving problems efficiently.

These codes, also known as Diagnostic Trouble Codes (DTCs), are alphanumeric combinations that identify specific problems in your vehicle’s engine, transmission, and emissions systems.

You’ll need a code reader to retrieve the codes, which are divided into two categories: generic (P0xxx) and manufacturer-specific (P1xxx).

The first character in an OBD-II code indicates the system associated with the fault, such as “P” for powertrain or “U” for network and integration.

For example, codes P0100-P0199 relate to fuel and air metering systems, which can include issues like Circuit High Voltage, Mass Air Flow, or System too rich.

Common Chevrolet DTC Codes

To better understand the issues plaguing your Chevrolet, it’s helpful to familiarize yourself with common Diagnostic Trouble Codes (DTCs).

These codes are part of the OBD-II system, which monitors your vehicle’s performance and alerts you to potential problems.

Some common Chevrolet DTC codes include P0128, indicating a faulty coolant thermostat, and P0420/P0430, related to catalyst system efficiency below threshold, often caused by a faulty catalytic converter or oxygen sensor.

You may also encounter P0171, indicating a system too lean, which can be caused by a vacuum leak, faulty fuel injector, or dirty Mass Air Flow sensor.

Other codes include P0300, indicating a random/multiple cylinder misfire, and P0440, related to an evaporative emission control system malfunction.

Reading and Interpreting Codes

You’ll need to understand how to read and interpret Chevrolet OBD-II codes to diagnose issues with your vehicle effectively.

When using a scan tool or code reader connected to your vehicle’s onboard diagnostics (OBD) port, you’ll retrieve a five-digit alphanumeric code that provides information about the system, subsystem, and specific problem.

The first character indicates the system, such as “P” for powertrain. The second character specifies the fault type, with “0” for generic faults and “1” for manufacturer-specific faults. The third and fourth characters provide additional information about the fault’s location or nature. The fifth character indicates the severity of the issue, with lower numbers indicating less severe problems.

Most Common Chevrolet OBD-II Trouble Codes