Chevy System Codes

Generic OBD-II

• All vehicles manufactured after 1996, regardless of the make or model, use the same basic diagnostic codes. These codes are the same on Fords, Hondas, Jeeps and every other vehicle including those manufactured by Chevrolet. OBD-II codes indicate problems in different areas of the vehicle. These areas are identified by the first character of the code. "P" stands for powertrain faults; "B" refers to the body problems; "C" indicates chassis electronic malfunctions; and "U" stands for network communication problems.
  
  

General Motors OBD-II

• Chevrolet, Buick, Oldsmobile and GMC are subsidiaries of General Motors. While the OBD-II system was meant to standardized diagnostics, wiggle room was left, allowing manufactures to define additional codes as needed. After all, no two brands of engine are exactly the same. The manufacturer-specific OBD-II codes use the same format as the generic codes and use the same character prefixes to identify the part of the vehicle where the error has been detected.
  
  

Distinguishing Generic from GM OBD-II

• Once codes have been retrieved from a Chevrolet's diagnostic system, there is a way to tell which codes are manufacturer-specific. For powertrain codes, any code starting with P1, P30, P31, P32 or P33 is manufacturer-specific. For chassis codes, any code starting with C1 or C2 is a GM code; GM's network communications codes begin with U1 and U2, and GM-specific body codes all begin with B1 or B2.
  
  

General Motors OBD-I

• Most Chevrolet vehicles predating 1995 use a flash code system. The diagnostic system can be placed into self-mode and the fault codes within the system will be relayed via a flashing "Check Engine" light. The codes can be diagnosed by counting the number and length of the flashes. GM fault codes are two character numbers -- the first number is represented by long flashes and the second by shorter flashes.
  
  

How to Access

• OBD-II codes require a special, handheld code reader or scanner. This device can be purchased at most auto parts stores. The scanner plugs in to the Chevrolet's data outlet, which is under the driver's side dashboard. Each device differs in how codes are retrieved so it's necessary to consult the product user manual for specific instructions.
  
  An OBD-I self-test does not use a scanner. Instead, the system can be jumped by connecting the "A" and "B" slots in the vehicle's data port. Then, turning on the electrical system will trigger the "Check Engine" light to start flashing.