Some common General Motors trouble codes include P1500, which indicates a problem with the starter signal circuit; P1514, in which the airflow to the throttle position sensor is too high; P1531, which indicates that the air conditioner's refrigerant is low; P1584, which shows that cruise control is disabled; and P1599, which detects an engine stall. Trouble codes from P1680 to P1687 show that there is a powertrain control module fault.
Trouble codes help vehicle owners or mechanics diagnose problems with a vehicle. When there is a problem that triggers a particular code, the Check Engine light appears on the vehicle's dashboard. In order to read the code, the owner or mechanic needs a code reader, which connects to a vehicle's instrument panel.
Codes do not provide exact information regarding the problem. Instead, they indicate a particular area where the problem exists. The owner or mechanic must carry out further diagnostic tests to determine the necessary repairs.
GM introduced an early version of its on-board diagnostic system in 1980. Early versions provided little diagnostic information, but over time the systems offered by GM and other automobile manufacturers improved. These systems now offer real-time data to aid in identifying problems. As of 1996, all vehicles sold in the United States must have an on-board diagnostic system.