Two-Trip Detection Logic

The diagnosis system operates in the normal mode during the normal vehicle use. It also has the check mode for technicians to simulate malfunction symptoms and make a trouble shooting. Most DTCs use 2 trip detection logic to prevent erroneous detection, which ensures the malfunction detection. Two-trip detection logic is when a malfunction is first detected, the malfunction is temporarily stored in the ECM memory (1st trip). By switching the ECM to the check mode when trouble shooting, the technicians can cause the MIL to light up for a malfunction that is only detected once or momentarily (hand-held tester only). See NORMAL MODE CODE RETRIEVAL  under RETRIEVING DIAGNOSTIC TROUBLE CODES.

If the same malfunction is detected again during the second drive test, this second detection causes the MIL to light up (2nd trip). However, the ignition switch must be turned OFF between the 1st 2 trip and 2nd 2 trip.