Monitors, Trips, Drive Cycles and Readiness Codes

2 Trip Detection Logic
The diagnostic codes 21, 25, 26, 27 and 71 use "2 trip detection logic". With this logic, when a logic malfunction is first detected, the malfunction is temporarily stored in the ECU memory. If the same case is detected again during the second drive test, this second detection causes the "CHECK ENGINE" Warning Light to light up.

The 2 trip repeats the same mode a 2nd time. (However, the IG SW must be turned OFF between the 1st time and 2nd time).