P06xx fault codes: Control unit and output circuits

Faults internal to the engine control unit or to its output circuits. Before suspecting the unit itself, which seldom fails, check grounds, connectors and battery voltage.

How to read this code

The letter P names the system: Powertrain. The next digit, 6, locates the fault: control unit and output circuits.

These codes are generic: they mean the same thing on every make. Some manufacturer tools display them with a two-digit suffix, such as P0101-00 or P010100: the suffix refines the fault type, and the base code keeps its meaning.

The codes of this family, part by part

Engine control unit

• P0600Serial Communication Link Malfunction
• P0601Internal Control Module Memory Check Sum Error
• P0602Control Module Programming Error
• P0603Internal Control Module Keep Alive Memory (KAM) Error
• P0604Internal Control Module RAM Error
• P0605Internal Control Module ROM Error (Module Identification Defined by SAE J1979)
• P0606PCM Processor Fault
• P0608Control Module VSS Output A Malfunction
• P0609Control Module VSS Output B Malfunction

Alternator (charging system)

• P0620Generator Control Circuit Malfunction
• P0621Generator Lamp L Control Circuit Malfunction
• P0622Generator Field F Control Circuit Malfunction

Dashboard signals from the engine control unit

• P0650Malfunction Indicator Lamp (MIL) Control Circuit Malfunction
• P0654Engine RPM Output Circuit Malfunction
• P0655Engine Hot Lamp Output Control Circuit Malfunction

Fuel level sensor

• P0656Fuel Level Output Circuit Malfunction