History Code

📖 YOUCANIC Automotive Glossary

A history code (stored code or past code) was previously active but the fault is no longer detected during current operation. The code remains in memory as a record that the problem occurred. History codes reveal intermittent problems — faults that come and go with temperature, vibration, or humidity. A crankshaft sensor with a failing internal connection might only lose signal at high temperatures, triggering a code that becomes history when it cools and works again.

Many DIYers ignore history codes because the warning light turned off, but these point to developing problems. The ECU extinguishes the MIL after three consecutive passing drive cycles, but history codes remain for 40-80 warm-up cycles. Before clearing, document them with freeze frame data — once cleared, information about intermittent problems is permanently lost. If you see a history code for a component that sometimes acts up, the code confirms which component to address.