Diagnostic Trouble Code Memory

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When the engine control module (ECM) detects a fault, a diagnostic trouble code with qualifier and status is stored in the control unit's diagnostic trouble code memory. Fault code storage has four status levels: , , and . When the engine control module (ECM) detects a fault, the diagnostic trouble code is stored with the status . If the fault persists the next time diagnostics is performed, diagnostic trouble code status switches to . At that time, the diagnostic trouble code will appear during normal DTC readout in appropriate diagnostics tool. If the fault is still active during the next operating cycle, the diagnostic trouble code receives the status . If the diagnostic trouble code causes the malfunction indicator lamp (MIL) to illuminate, that process starts now. For more information, see "Lighting the malfunction indicator lamp (MIL)" below.

If an existing fault disappears and does not return, the engine control module (ECM) stores the code (after a number of fault-free operating cycles depending on the fault code and previous status) with the status . In this status, the diagnostic trouble code remains until the engine control module (ECM) is cleared of diagnostic trouble codes or the power to it is cut off.

HINT: A diagnostic trouble code with the status can be read in appropriate diagnostics tool using extended DTC readout. This is often useful when explaining a customer-reported symptom that occurred some time ago.