Serial Data Communications

A "TRIP" is defined as a key On-Run-key Off cycle in which all the criteria were met for a given diagnostic test to run. During any given drive cycle, key On-Run-key Off criteria may or may not have been met to perform all diagnostic tests. No "TRIP" will occur for a given diagnostic until the vehicle is driven in such a manner as to meet all the enable criteria. If a test is desired on a particular subsystem to determine if it "passes" or "fails" refer to the specific DTC for test parameters. The parameters are calibrated conditions the ECM requires in order to perform the test. If a test has not been run, monitor the Scan tool pass/fail DTC status at the time the parameters have been met.

The Scan tool will display whether the DTC in the ECM's memory is active or history. The following describes the active/history criteria for each DTC.

Active - An active DTC indicates that the last time a diagnostic test was performed on a particular system or sub-system it failed. A problem may no longer exist, but since another test has not been run, the fault still appears active.

History - A history DTC indicates there have been enough faults detected to determine a problem exists. Diagnostic trouble codes that are calibrated to turn On the MIL on the first occurrence, and all non-emission codes will be stored in history as soon as a fault becomes active. However a diagnostic DTC that is calibrated to turn on the MIL on the second occurrence (Type B) will become active on one trip and then on the second occurrence of the DTC will he stored in history and the MIL will be illuminated. Regulations require that the MIL be illuminated for three trips, when any emission related diagnostic fault occurs. Therefore, it will take three ignition cycles in a row, with three passing tests, to turn Off the lamp. The indicator provides information to determine which diagnostic is still illuminating the MIL and whether a fault exists or not.

IMPORTANT: If a catalyst damaging misfire occurs and a misfire DTC sets (type A), the MIL lamp will be turned Off after three passed trips.

Lamp Requested - Indicates whether a diagnostic trouble code is requesting the MIL to be illuminated.

It is important to remember that the DTC as well as any stored malfunction history will be erased if the vehicle battery has been disconnected or a clear DTC command is issued to the ECM. DTCs and malfunction history records will also be erased if 40 passes (only one pass per ignition cycle is counted) have been recorded without any faults. All emission (DTC Type A or B) and non-emission (DTC Type C or D) codes require this 40 pass criteria.

Warm Up Cycle
A warm-up cycle is defined as engine temperature reaching a minimum of 71°C (160°F) and a rise in temperature of at least 22°C (40°F) over the course of a trip.