Trip Detection Logic

WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2000 Isuzu VehiCROSS, 2000 Isuzu Trooper, 2000 Isuzu Rodeo, 2000 Isuzu Hombre, and 2000 Isuzu Amigo. However, it is still accessible from the selected car via links, so may be relevant.

OBD-II data streams are prioritized. When 2 messages attempt to establish communications on a data line at the same time, only the message with higher priority will continue. A new segment of the software called the Diagnostic Executive coordinates the protocol for recording and displaying diagnostic procedures.

Trip is a single key-on-run-key-off cycle which satisfies the enable criteria for a specific diagnostic function. Criteria may vary slightly to satisfy differing diagnostic functions. For this reason, the definition of trip may vary with the specific application. The Diagnostic Executive uses trip information in setting and erasing DTCs.

After engine has reached normal operating temperature, Diagnostic Executive checks if on-board diagnostic tests have been completed since last ignition cycle. Executive checks if tests have passed during current ignition cycle, and if fault(s) identified by diagnostic tests is currently active. Executive also checks if fault identified has been active during current ignition cycle and what operating conditions were present at the time of failure.

A malfunction will set one of 4 types of DTC:

Type A

Turns the MIL on the first time an emission related failure occurs. The MIL may flash at a rate of once per second to alert the operator of potentially damaging levels of misfire, which could possibly destroy the catalytic converter. History DTC, Freeze Frame and Fail Record are stored, and Fail Records are updated each time current diagnostic test fails.

Type B

Will only turn MIL on if an emission related condition occurs during 2 consecutive driving cycles. Conditions such as incorrect fuel trim will be stored in the freeze-frame data until the fault is detected a second time. If the fault is not detected during 3 consecutive driving cycles, the MIL light will be turned off.

Type C

This is a non-emission related type DTC and will not activate the MIL. It will turn on a CHECK TRANSMISSION service light, or other non-MIL service reminder light.

Type D (Except Hombre)

Is non-emission related, and will not turn on service light, but will store DTCs for present faults.

Type X (Hombre)

These DTCs are coded into PCM software, but will not set because associated hardware is not installed, or diagnostic test is not required for vehicle's emissions package.