CRP919E 919E User Manual

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LAUNCH Professional 919E User Manual

1.6.1 Continuous Monitors

Some of the vehicle components or systems are continuously tested by the

vehicle’s OBD II system, while others are tested only under specic vehicle

operating conditions. The continuously monitored components listed below are

always ready:

1. Misre Monitor

This Monitor continuously checks for engine misres. A misre occurs when

the air-fuel mixture in the cylinder does not ignite. The misre Monitor uses

changes in crankshaft speed to sense an engine misfire. When a cylinder

misres, it no longer contributes to the speed of the engine, and engine speed

decreases each time the affected cylinder(s) misfire. The misfire Monitor

is designed to sense engine speed fluctuations and determine from which

cylinder(s) the misre is coming, as well as how bad the misre is.

There are three types of engine misres, Types 1, 2, and 3.

• Type 1 and Type 3 misres are two-trip monitor faults. If a fault is sensed

on the rst trip, the computer temporarily saves the fault in its memory as

a Pending Code. The MIL is not commanded on at this time. If the fault is

found again on the second trip, under similar conditions of engine speed,

load and temperature, the computer commands the MIL “On,” and the code

is saved in its long term memory.

• Type 2 misres are the most severe type of misre. When a Type 2 misre

is sensed on the rst trip, the computer commands the MIL to light when

the misre is sensed. If the computer determines that a Type 2 misre is

severe, and may cause catalytic converter damage, it commands the MIL

to “flash” once per second as soon as the misfire is sensed. When the

misre is no longer present, the MIL reverts to steady “On” condition.

The Misfire Monitor is supported by both “spark ignition” vehicles and

“compression ignition” vehicles.

2. Fuel System Monitor

This Monitor uses a Fuel System Correction program, called Fuel Trim, inside

the on-board computer. Fuel Trim is a set of positive and negative values that

represent adding or subtracting fuel from the engine. This program is used

to correct for a lean (too much air/not enough fuel) or rich (too much fuel/not

enough air) air-fuel mixture. The program is designed to add or subtract fuel,

as needed, up to a certain percent. If the correction needed is too large and

exceeds the time and percent allowed by the program, a fault is indicated by

the computer.

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919E User Manual - Page 15