DNOSE User Manual

Loading ...

DN606 Automotive Diagnostic Tool User's Manual

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 misre. 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) misre. The misre Monitor is designed to sense

engine speed fluctuations and determine from which cylinder(s) the misfire 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 misfires 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 “ash”

once per second as soon as the misfire is sensed. When the misfire 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.

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

“compression ignition” vehicles. The Fuel System Monitor may be a “One-Trip”

or “Two-Trip” Monitor, depending on the severity of the problem.

3. Comprehensive Components Monitor (CCM)

Loading ...

User Manual - Page 16