What does it mean?
You’re probably already familiar with how the modern OBDII system works in your car. If the MIL or CEL (malfunction indicator lamp or check-engine light) illuminates, this means that the ECU (engine control unit) has detected a fault, of some type, and that the powertrain is running in open loop mode, also known as “limp-home” mode. To ensure proper operation, you should hook up a scan tool and retrieve the DTCs (diagnostic trouble codes) stored in ECU memory.
Given that there is a maximum of 10,000 DTC P-codes available, having a specific DTC to point you in the right direction is indeed helpful. There is one DTC that stymies people almost every time, because it seems to make no sense. Defined as “No Diagnostic Trouble Codes Reported,” DTC P0000 should never show up on a scan tool screen. Indeed, if there are no drivability problems and no MIL, hooking up a scan tool generally results in a blank or “no codes” reading.
There are two cases, however, when DTC P0000 may show up, even if you have drivability problems or an illuminated MIL.