Mitsubishi Eclipse. Technical Information Manual (1994) - part 13

ENGINE <NON-TURBO>   Control System

ELECTRIC EGR TRANSDUCER

The Electronic EGR Transducer (EET) contains an

electrically operated solenoid and a back-pressure
controlled vacuum transducer. The PCM operates

the solenoid based on inputs from the multi-port
fuel injection system. The EET and EGR valve are
serviced as an assembly.

When the PCM de-energizes the solenoid, vacuum
does not reach the transducer. Vacuum flows to
the transducer when the PCM energizes the sole-

noid.

When exhaust system back-pressure becomes high
enough, it fully closes a bleed valve in the vacuum
transducer. When the PCM energizes the solenoid

and back-pressure closes the transducer bleed
valve, vacuum flows through the transducer to oper-
ate the EGR valve.

Energizing the solenoid, but not fully closing the

transducer bleed hole (because of low back-pres-
sure), varies the strength of the vacuum signal ap-

plied to the EGR valve. Varying the strength of the

vacuum signal changes the amount of EGR supplied
to the engine. This provides the correct amount
of exhaust gas recirculation for different operating
conditions.

The EET and EGR valve mount to the rear of the
cylinder head.

ENGINE <NON-TURBO>   Control Svstem

1-31

DIAGNOSTIC SYSTEM

MALFUNCTION INDICATOR LAMP (MIL)

The PCM provides the ground path for the malfunc-
tion indicator lamp (Check Engine light in the gauge
cluster on the instrument panel). The lamp comes

on each time the ignition key is turned ON and
stays on for a 3 seconds bulb test.

The MIL lamp stays on continuously, when the PCM

has entered a Limp-in mode or identified a failed
emission component. During Limp-in Mode, the

PCM attempts to keep the system operational. The
malfunction indicator lamp signals the need for im-
mediate service. In limp-in mode, the PCM compen-

sates for the failure of certain components that send
incorrect signals by substituting inputs from other
sensors.

GENERAL INFORMATION

The diagnostic system for vehicles with a manual
transaxle conforms to OBD-II, where the one for
vehicles with an automatic transaxle conforms to

OBD II has been developed to allow to meet the
requirements of the Federal Clean Air Act and
California Air Resources Board (CARB) legislation.

It is impractical (and very expensive) to provide

every vehicle on the road with the equipment neces-
sary to measure emissions of carbon monoxide

(CO), hydrocarbons (HC) and oxides of nitrogen

 Instead, the proven emissions control de-

vices available for these vehicles are checked for

proper operation.

MIL ILLUMINATION:

If the PCM detects active engine misfire severe

enough to cause catalyst damage, it flashes the
malfunction indicator lamp (Check Engine light). ,At
the same time the PCM also sets a diagnostic trouble
code. <vehicles with manual transaxle>

The malfunction indicator lamp can also display
diagnostic trouble codes. Cycle the ignition switch

on, off, on, off, on, within five seconds and the PCM
displays any diagnostic trouble codes stored in
memory.

The diagnostic trouble codes can also be read by
the scan tool.

NOTE

When monitoring the misfire and fuel system, if
trouble is detected, the MIL will light until the comple-
tion of the next operation cycle (trip) following the
cycle where the trouble is detected. In addition,

if the detected trouble may cause damage to the
catalytic converter, the MIL will light immediately.
However, if the trouble is not detected in the
succeeding trip under almost the same driving condi-
tion, MIL should go out. And if the same trouble
will not be detected within 80 trips following the
trip where the trouble is detected, the diagnostic
trouble code will be erased.

. FAULT ON TWO SUCCESSIVE TRIPS

. (MIL ON) NO FAULT ON THREE

SUCCESSIVE TRIPS

MIL ON

MIL OFF

FAULT CODE STORAGE:

. FAULT ON TWO SUCCESSIVE TRIPS

. (DTC) NO FAULT ON 40-80

SUCCESSIVE TRIPS

DIAGNOSTIC TROUBLE

CODE STORED

DIAGNOSTIC TROUBLE
CODE ERASED

1-32

ENGINE <NON-TURBO> 

 Control System

In addition to illuminating the MIL lamp, a diagnostic

trouble code (DTC) is stored in the Powertrain Con-
trol Module (PCM) and can be retrieved by a service
technician using a diagnostic scan tool.

To meet OBD-II requirements the following systems

must be monitored:

 Catalyst

l 

Fuel System

l 

Misfire

l 

Oxygen Sensor and Oxygen Sensor Heater

l 

Secondary Air

l 

Evaporative System (Purge)

l 

Exhaust Gas Recirculation

l

Any other input or output component that can
affect emissions

The operating conditions of the components can
be monitored using MUT-II scan tool, as well as
general purpose scan tools. The OBD II system
monitors are different. They are checks made by

DIAGNOSTIC SYSTEM OPERATION

Trip Indicator

“Trip” is a difficult concept to define because the
requirements for a trip vary depending on the test
being run. These conditions can include seemingly
unrelated items such as driving style, length of trip,
and ambient temperature. The minimum require-
ment for a trip is that it includes one key cycle with

the vehicle having to meet certain enabling condi-
tions before a test is performed. Vehicle tests vary

in length and may be performed only once per trip

or may be performed continuously. If the pertinent
enabling conditions are not met during that key cycle,
the tests may not run at all.

NOTE
In California and other states requiring the PCM

to indicate that all monitors have passed before

issuing license plates, removing the vehicle’s battery

or using the MUT-II scan tool to erase 

 before

testing erases any record of passing a monitor. If
the monitor does not complete a trip on subsequent

key cycles, the vehicle will fail a licensing test.

What constitutes a trip for a particular OBD test

is important because in many instances, the vehicle
must fail a test on more than once before the MIL
is illuminated and a DTC is recorded. Tests that
illuminate the MIL when a single failure is recorded

are known as 

 trip” monitors. “Two trip” monitors

the 

 software to determine not only if these

specific systems are operating, but if they are operat-
ing within pre-established limits. While OBD I tests
measure a component’s electrical operation, OBD

II monitors check a system’s performance.

The California Air Resources Board (CARB) moni-
tors emission system repairs from several California
dealers. If a specific component or system fails on
more than 4% of the vehicles sampled, the manufac-
turer is required to research and evaluate the rea-
sons. If the failure is not attributable to owner negli-
gence or misuse, a component failure rate of 4%
could lead to vehicle recalls. The federal government
is considering a similar program. The manufacturer
is relying on its technicians throughout the country
to appropriately diagnose emissions concerns and
replace only those parts that have failed. The sloppy
practice of “hanging” parts on a car under emissions

warranty could lead to an unnecessary (and expen-
sive) fleet-wide recall.

allow the system to double check itself and help
prevent unnecessary MIL illumination.

If the conditions to run the test are not met on consec-
utive key cycles, the information from the first test
is not lost. The diagnostic system waits until the
next time the appropriate test conditions occur and

continues the count.

If this is a “two trip fault” and the test failed the

first time, a malfunction the second consecutive
time the test is run (even if there were ten key
cycles between these tests) will illuminate the MIL.

If the malfunction does not occur the second time

the test is run, the MIL lamp does not illuminate
and no DTC is recorded.

The diagnostic system can turn the MIL off if it re-
cords three consecutive trips where the system
passes the test. However, with the misfire and fuel
monitors, the system must past the test under the
same circumstances (within 375 rpm) under which
it failed the test.

In summary, it is the diagnostic system’s job to deter-

mine if the conditions are appropriate for a test

to be run, know the definition of a trip for each
test, and record the results of each test when it

is run.

ENGINE <NON-TURBO>   Control System

1-33

DTC Identification, Maturation, and Erasure

Once a test has been run, the diagnostic system
determines whether the system has passed or failed.

It must then determine if the test has failed the

specified number of times required to illuminate the

MIL. If not, the diagnostic system stores a maturing

code. When this test is run again (on the next “trip”)
the results are once again either pass or fail. If
the component fails the test, a code “matures,” and
a DTC is set. The MIL lamp is illuminated if an
emission component is involved. If the component

or system passes the test a specified number of
times, the maturing code is erased.

NOTE
It is important to understand that a system need
not fail a test under exactly the same conditions

for a code to nature and trigger the MIL.

Freeze Frame Data Storage and Erasure

All monitored systems provide “freeze frame” data
of the vehicle’s operating conditions when a matur-

ing code was set. This information can be retrieved
using the diagnostic scan tool and may help a techni-
cal pinpoint the source of a concern more quickly.

When there are multiple monitor failures, the first
to occur is stored in freeze frame. The exceptions
are the misfire and fuel system monitors. They have

priority and can write over other freeze frame data.

Freeze Frame Priority

The freeze frame only indicates the operating condi-
tions under which the maturing code was set. While
these conditions are usually the same as those
which trigger the maturation of the DTC, there can

be exceptions. This first condition is important for

fuel system and misfire DTC’s as it is the condition

MIL Illumination

As described earlier, the PCM diagnostic system

is responsible for operation of the MIL lamp. This
is an important function as unnecessary operation
of this lamp has a negative effect on customer satis-

faction. In most cases, if a component or system

passes diagnostics on three consecutive trips after

the MIL has been illuminated, the MIL is extin-
guished. This explains how customers can note
that the “Check Engine” light went on, and then
off, on its own. The OBD II has reconsidered its

diagnosis. The DTC remains in the memory until

DTC’s are erased if the component passes the diag-
nostic test in the course of a number of subsequent

warm-up cycles. The number of trips required for
this is usually 40. This is why it is best to attempt
to diagnose intermittent problems soon after they
occur. While initially a DTC may have been available,
subsequent trips (which passed the diagnostic test)

have erased the code. The OBD II system, based
on the latest inputs it received, reconsidered its
diagnosis on this intermittent concern.

Of course, a diagnostic scan tool can be used to
erase DTC’s at any time. In addition, DTC’s (along
with records of successful trips) are erased whenev-
er the vehicle’s battery is disconnected.

Information in the freeze frame includes:

l 

Diagnostic Trouble Code (DTC)

l 

Engine rpm

l 

Engine load

l

Fuel trim (short term and long term)

 Engine coolant temperature

l 

Manifold absolute pressure

l 

Operation mode (open or closed loop)

l 

Vehicle speed

the vehicle must repeat successfully during a test
to allow the diagnostic system to erase a DTC and
turn off the MIL on its own.

Should the diagnostic system determine that the

DTC can be erased, the freeze frame related to

that code is also eliminated.

 

a larger number of warm-up cycles (40) have been
successfully completed.

The MIL flashed in misfire situations where contin-

ued driving could damage the catalytic converter.
Continued driving of the vehicle when this condition
occurs is not recommended.

The MIL can be used to produce diagnostic trouble
codes. Quickly turning the key to the RUN position
three times allows the MIL to flash out any existing
flash codes.