Some common GM engine diagnostics codes include P1508 and P1509, which indicate that the idle air control system is idling too low or too high; P1524, which indicates that the throttle position sensor out of range or improperly adjusted; and P1566, which indicates that the speed control system is malfunctioning or engine RPM is too high. Other codes include P1620, which indicates that the engine coolant is low.
Any time an engine component functions below or above recommended thresholds, the vehicle’s computer generates a code. The Check Engine light comes on whenever the computer generates the code, warning the driver about the existence of the issue. This light remains on until a mechanic clears the code from the computer.
Mechanics obtain diagnostic codes by connecting a code reader or scan tool to the front console of the vehicle, near the steering column. In most circumstances, the engine diagnostic code does not pinpoint the actual part that is causing a problem. Instead, it allows a mechanic to determine the circuit, system or sensor from which the issue stems. Mechanics usually carry out further tests to determine the actual source of the malfunction before making any repairs. Codes should not be cleared until after correcting the underlying issues.