Lamp health "CHECK ENGINE" The dashboard checks the ECU each time the ignition key is turned to "ON". The lamp should burn for 2 seconds and then go out. Under normal circumstances, the lamp does not remain lit when the engine is running.
If the warning light is on while the engine is running, the ECU has detected a system problem. The fault could be either loss of signal or signal out of range, too large or too small. Additionally, when the lamp is lit, the ECU uses a default or fail-safe mode in which preset values replace a defective or missing signal.
If the Accord or Prelude service connector is connected during diagnostics, the CHECK ENGINE lamp is on even if there is no problem. When the repair or diagnosis is complete, the memory should be checked for any stored codes and cleared if necessary.