Isuzu Rodeo UE. Manual — part 170

6E1–51

RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

f

Exhaust leaks

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HO2S contamination

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Alternate fuels

Exhaust system leaks may cause the following:

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Preventing a degraded catalyst from failing the
diagnostic.

f

Causing a false failure for a normally functioning
catalyst.

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Preventing the diagnostic from running.

Some of the contaminants that may be encountered are
phosphorus, lead, silica, and sulfur. The presence of
these contaminants will prevent the TWC diagnostic from
functioning properly.

Three–Way Catalyst Oxygen Storage Capacity
The Three–Way catalyst (TWC) must be monitored for
efficiency. To accomplish this, the control module
monitors the pre–catalyst HO2S and post–catalyst HO2S
oxygen sensors. When the TWC is operating properly,
the post–catalyst oxygen sensor will have significantly
less activity than the pre–catalyst oxygen sensor. The
TWC stores and releases oxygen as needed during its
normal reduction and oxidation process. The control
module will calculate the oxygen storage capacity using
the difference between the pre–catalyst and post catalyst
oxygen sensor’s voltage levels. If the activity of the
post–catalyst oxygen sensor approaches that of the
pre–catalyst oxygen sensor, the catalyst’s efficiency is
degraded.
Stepped or staged testing level allow the control module
to statistically filter test information. This prevents falsely
passing or falsely failing the oxygen storage capacity test.
The calculations performed by the on–board diagnostic
system are very complex. For this reason, post catalyst
oxygen sensor activity should not be used to determine
oxygen storage capacity unless directed by the service
manual.
Two stages are used to monitor catalyst efficiency.
Failure of the first stage will indicate that the catalyst
requires further testing to determine catalyst efficiency.
The second stage then looks at the inputs from the pre
and post catalyst HO2S sensors more closely before
determining if the catalyst is indeed degraded. This
further statistical processing is done to increase the
accuracy of oxygen storage capacity type monitoring.
Failing the first (stage 1) test DOES NOT indicate a failed
catalyst. The catalyst may be marginal or the fuel sulfur
content could be very high.
Aftermarket HO2S characteristics may be different from
the original equipment manufacturer sensor. This may
lead to a false pass or a false fail of the catalyst monitor
diagnostic. Similarly, if an aftermarket catalyst does not
contain the same amount of cerium as the original part,
the correlation between oxygen storage and conversion
efficiency may be altered enough to set a false DTC.

MISFIRE MONITOR DIAGNOSTIC

OPERATION

Misfire Monitor Diagnostic Operation

The misfire monitor diagnostic is based on crankshaft
rotational velocity (reference period) variations. The PCM
determines crankshaft rotational velocity using the
crankshaft position sensor and camshaft position sensor.
When a cylinder misfires, the crankshaft slows down
momentarily. By monitoring the crankshaft and camrhaft
position sensor signals, the PCM can calculate when a
misfire occurs.
For a non–catalyst damaging misfire, the diagnostic will
be required to monitor a misfire present for between
1000–3200 engine revolutions.
For catalyst–damaging misfire, the diagnostic will
respond to misfire within 200 engine revolutions.
Rough roads may cause false misfire detection. A rough
road will cause torque to be applied to the drive wheels
and drive train. This torque can intermittently decrease
the crankshaft rotational velocity. This may be falsely
detected as a misfire.

Misfire Counters

Whenever a cylinder misfires, the misfire diagnostic
counts the misfire and notes the crankshaft position at the
time the misfire occurred. These ”misfire counters” are
basically a file on each engine cylinder. A current and a
history misfire counter are maintained for each cylinder.
The misfire current counters (Misfire Cur #1–4) indicate
the number of firing events out of the last 200 cylinder
firing events which were misfires. The misfire current
counter will display real time data without a misfire DTC
stored. The misfire history counters (Misfire Hist#1–4)
indicate the total number of cylinder firing events which
were misfires. The misfire history counters will display 0
until the misfire diagnostic has failed and a DTC P0300 is
set. Once the misfire DTC P0300 is set, the misfire history
counters will be updated every 200 cylinder firing events.
A misfire counter is maintained for each cylinder.
If the misfire diagnostic reports a failure, the diagnostic
executive reviews all of the misfire counters before
reporting a DTC. This way, the diagnostic executive
reports the most current information.
When crankshaft rotation is erratic, a misfire condition will
be detected. Because of this erratic condition, the data
that is collected by the diagnostic can sometimes
incorrectly identify which cylinder is misfiring.
Use diagnostic equipment to monitor misfire counter data
on OBD II–compliant vehicles. Knowing which specific
cylinder(s) misfired can lead to the root cause, even when
dealing with a multiple cylinder misfire. Using the
information in the misfire counters, identify which
cylinders are misfiring. If the counters indicate cylinders
numbers 1 and 4 misfired, look for a circuit or component
common to both cylinders number 1 and 4.
Misfire counter information is located in the ”Specific
Eng.” menu, ”Misfire Data” sub–menu of the data list.
The misfire diagnostic may indicate a fault due to a
temporary fault not necessarily caused by a vehicle

6E1–52

RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

emission system malfunction. Examples include the
following items:

f

Contaminated fuel

f

Low fuel

f

Fuel–fouled spark plugs

f

Basic engine fault

FUEL TRIM SYSTEM MONITOR

DIAGNOSTIC OPERATION

Fuel Trim System Monitor Diagnostic
Operation

This system monitors the averages of short–term and
long–term fuel trim values. If these fuel trim values stay at
their limits for a calibrated period of time, a malfunction is
indicated. The fuel trim diagnostic compares the
averages of short–term fuel trim values and long–term
fuel trim values to rich and lean thresholds. If either value
is within the thresholds, a pass is recorded. If both values
are outside their thresholds, a rich or lean DTC will be
recorded.
The fuel trim system diagnostic also conducts an intrusive
test. This test determines if a rich condition is being
caused by excessive fuel vapor from the EVAP canister.
In order to meet OBD II requirements, the control module
uses weighted fuel trim cells to determine the need to set
a fuel trim DTC. A fuel trim DTC can only be set if fuel trim
counts in the weighted fuel trim cells exceed
specifications. This means that the vehicle could have a
fuel trim problem which is causing a problem under
certain conditions (i.e., engine idle high due to a small
vacuum leak or rough idle due to a large vacuum leak)
while it operates fine at other times. No fuel trim DTC
would set (although an engine idle speed DTC or HO2S
DTC may set). Use the Tech 2 to observe fuel trim counts
while the problem is occurring.
A fuel trim DTC may be triggered by a number of vehicle
faults. Make use of all information available (other DTCs
stored, rich or lean condition, etc.) when diagnosing a fuel
trim fault.

Fuel Trim Cell Diagnostic Weights

No fuel trim DTC will set regardless of the fuel trim counts
in cell 0 unless the fuel trim counts in the weighted cells
are also outside specifications. This means that the
vehicle could have a fuel trim problem which is causing a
problem under certain conditions (i.e. engine idle high due
to a small vacuum leak or rough due to a large vacuum
leak) while it operates fine at other times. No fuel trim DTC
would set (although an engine idle speed DTC or HO2S
DTC may set). Use the Tech 2 to observe fuel trim counts
while the problem is occurring.

6E1–53

RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

ON–BOARD DIAGNOSTIC (OBD II) SYSTEM CHECK

D06RX036

Circuit Description

The on–board diagnostic system check is the starting
point for any driveability complaint diagnosis. Before
using this procedure, perform a careful visual/physical
check of the PCM and engine grounds for cleanliness and
tightness.
The on–board diagnostic system check is an organized
approach to identifying a problem created by an
electronic engine control system malfunction.

Diagnostic Aids

An intermittent may be caused by a poor connection,
rubbed–through wire insulation or a wire broken inside the
insulation. Check for poor connections or a damaged
harness. Inspect the PCM harness and connectors for
improper mating, broken locks, improperly formed or

damaged terminals, poor terminal–to–wire connection,
and damaged harness.

Test Description

Number(s) below refer to the step number(s) on the
Diagnostic Chart:
1. The MIL (”Check Engine” lamp) should be ON

steady with the ignition ON/engine OFF. If not,
isolate the malfunction in the MIL circuit.

2. Checks the Class 2 data circuit and ensures that the

PCM is able to transmit serial data.

3. This test ensures that the PCM is capable of

controlling the MIL and the MIL driver circuit is not
shorted to ground.

4. If the engine will not start, the Cranks But Will Not

Run chart should be used to diagnose the condition.

6E1–54

RODEO X22SE 2.2L ENGINE DRIVEABILITY AND EMISSION

7. A Tech 2 parameter which is not within the typical

range may help to isolate the area which is causing
the problem.

10. This vehicle is equipped with a PCM which utilizes

an electrically erasable programmable read only
memory (EEPROM). When the PCM is replaced,
the new PCM must be programmed. Refer to PCM
Replacement and Programming Procedures in
Powertrain Control Module (PCM) and Sensors.

On–Board Diagnostic (OBD II) System Check

Step

Action

Value(s)

Yes

No

1

1. Ignition ON, engine OFF.
2. Observe the malfunction indicator lamp (MIL or

”Check Engine lamp”).

Is the MIL (”Check Engine lamp”) ON?

—

Go to

Step 2

Go to

No MIL

2

1. Ignition OFF.
2. Install a Tech 2.
3. Ignition ON.
4. Attempt to display PCM engine data with the Tech 2.

Does the Tech 2 display PCM data?

—

Go to

Step 3

Go to

Step 8

3

1. Using the Tech 2 output tests function, select MIL

dash lamp control and command the MIL OFF.

2. Observe the MIL.

Did the MIL turn OFF?

—

Go to

Step 4

Go to MIL

(”Check

Engine

Lamp”) On

Steady

4

Attempt to start the engine.

Did the engine start and continue to run?

—

Go to

Step 5

Go to

Cranks

But Will Not

Run

5

Select ”Display DTCs” with the Tech 2.

Are any DTCs stored?

—

Go to

Step 6

Go to

Step 7

6

Are two or more of the following DTCs stored? P0107,
P0113, P0118, P0122, P0123.

—

Go to

“Multiple

PCM

Information

Sensor DTCs

Set”

Go to

applicable
DTC table

7

Compare PCM data values displayed on the Tech 2 to
the typical engine scan data values.

Are the displayed values normal or close to the typical
values?

—

Go to

“Typial

Scan” Data

Value

Go to

indicated

Component

System
Checks

8

1. Ignition OFF, disconnect the PCM.
2. Ignition ON, engine OFF.
3. Check the Class 2 data circuit for an open, short to

ground, or short to voltage. Also, check the DLC
ignition feed circuit for an open or short to ground
and the DLC ground circuits for an open.

4. If a problem found, repair as necessary.

Was a problem found?

—

Go to

Step 2

Go to

Step 9