Erase Fault Codes

📖 YOUCANIC Automotive Glossary

Code Clearing (Erasing DTCs)

Code clearing, also called erasing or resetting DTCs, is the process of using an OBD2 scanner to command the ECU to delete all stored diagnostic trouble codes, turn off the check engine light (MIL), reset freeze frame data, and reset all readiness monitors to “not complete” or “not ready” status. When you select “Clear Codes” or “Erase DTCs” on your scanner, it sends a Mode $04 command to the ECU that performs all of these resets simultaneously. This is an important diagnostic step performed after a repair to verify the fix — once codes are cleared, you drive the vehicle through its drive cycle to see if the code returns. If it does, the repair was unsuccessful; if it doesn’t and the monitors complete and pass, the repair was successful.

However, code clearing should be used strategically, not as a first step. A common mistake DIYers make is clearing codes before reading freeze frame data, history codes, and pending codes — once cleared, this diagnostic information is permanently lost. Always record all codes, freeze frame data, and monitor status before clearing. Another critical consideration is emissions testing: clearing codes resets all readiness monitors to “not ready,” and most states require a certain number of monitors to show “ready” (complete) before the vehicle can pass an emissions inspection. Depending on the vehicle, it can take 50-200 miles of varied driving (highway, city, hot start, cold start) to complete all monitors. If you clear codes right before an emissions test, the vehicle will fail for incomplete monitors even if the underlying problem is fixed. Disconnecting the battery has a similar effect to clearing codes on most vehicles — it resets adaptive memory, learned fuel trims, idle settings, and transmission shift patterns in addition to clearing codes, which means the vehicle may run rough or shift differently for a period while the ECU relearns these values. Using your scanner’s clear function is generally preferred over a battery disconnect because it only resets diagnostic data without affecting learned operating parameters.