Isuzu Trooper (1998-2002 year). Manual - part 288

6E–65

ENGINE DRIVEABILITY AND EMISSIONS

Knock Sensor Diagnosis

The Tech 2 has two data displays available for diagnosing
the knock sensor (KS) system.  The two displays are
described as follows:

D

“Knock Retard” indicates the number of degrees that
the spark timing is being retarded due to a knock
condition.

D

“KS Noise Channel” indicates the current voltage level
being monitored on the noise channel.

DTCs P0325 and P0327 are designed to diagnose the KS
module, the knock sensor, and the related wiring.  The
problems encountered with the KS system should set a
DTC. However, if no DTC was set but the KS system is
suspect because of a detonation complaint, refer to
Detonation/Spark Knock in Symptoms.

Powertrain Control Module (PCM)

Diagnosis

To read and clear diagnostic trouble codes, use a Tech 2.
IMPORTANT:

Use of a Tech 2 is recommended to clear

diagnostic trouble codes from the PCM memory.
Diagnostic trouble codes can also be cleared by turning
the ignition “OFF” and disconnecting the battery power
from the PCM for 30 seconds.  Turning off the ignition and
disconnecting the battery power from the PCM will cause
all diagnostic information in the PCM memory to be
cleared.  Therefore, all the diagnostic tests will have to be
re-run.
Since the PCM can have a failure which may affect only
one circuit, following the diagnostic procedures in this
section will determine which circuit has a problem and
where it is.
If a diagnostic chart indicates that the PCM connections
or the PCM is the cause of a problem, and the PCM is
replaced, but this does not correct the problem, one of the
following may be the reason:

D

There is a problem with the PCM terminal connections.
The terminals may have to be removed from the
connector in order to check them properly.

D

The problem is intermittent.  This means that the
problem is not present at the time the system is being
checked.  In this case, refer to the 

Symptoms portion of

the manual and make a careful physical inspection of
all component and wiring associated with the affected
system.

D

There is a shorted solenoid, relay coil, or harness.
Solenoids and relays are turned “ON” and “OFF” by the
PCM using internal electronic switches called drivers.
A shorted solenoid, relay coil, or harness will not
damage the PCM but will cause the solenoid or relay to
be inoperative.

Multiple PCM Information Sensor

DTCS Set

Circuit Description

The powertrain control module (PCM) monitors various
sensors to determine the engine operating conditions.
The PCM controls fuel delivery, spark advance,
transmission operation, and emission control device
operation based on the sensor inputs.

The PCM provides a sensor ground to all of the sensors.
The PCM applies 5 volts through a pull-up resistor, and
determines the status of the following sensors by
monitoring the voltage present between the 5-volt supply
and the resistor:

D

The engine coolant temperature (ETC) sensor

D

The intake air temperature (IAT) sensor

D

The transmission fluid temperature (TFT) sensor

The PCM provides the following sensors with a 5-volt
reference and a sensor ground signal:

D

The exhaust gas recirculating (EGR) pintle position
sensor

D

The throttle position (TP) sensor

D

The manifold absolute pressure (MAP) sensor

The PCM monitors the separate feedback signals from
these sensors in order to determine their operating
status.

Diagnostic Aids

IMPORTANT:

Be sure to inspect PCM and engine

grounds for being secure and clean.
A short to voltage in one of the sensor input circuits may
cause one or more of the following DTCs to be set:

D

P0108

D

P0113

D

P0118

D

P0123

D

P0560

D

P0712

D

P0406

IMPORTANT:

If a sensor input circuit has been shorted

to voltage, ensure that the sensor is not damaged. A
damaged sensor will continue to indicate a high or low
voltage after the affected circuit has been repaired.  If the
sensor has been damaged, replace it.
An open in the sensor ground circuit between the PCM
and the splice will cause one or more of the following
DTCs to be set:

D

P0108

D

P0113

D

P0118

D

P0123

D

P0712

D

P0406

A short to ground in the 5-volt reference A or B circuit will
cause one or more of the following DTCs to be set:

D

P0107

D

P0122

In the 5-volt reference circuit A, between the PCM and the
splice, will cause one or more of the following DTCs to be
set:

D

P0122

In the 5-volt reference circuit B, between the PCM and the
splice, will cause one or more of the following DTCs to be
set:

D

P0107

Check for the following conditions:

6E–66

ENGINE DRIVEABILITY AND EMISSIONS

D

Poor connection at PCM. Inspect the harness
connectors for backed-out terminals, improper mating,
broken locks, improperly formed or damage terminals,
and a poor terminal-to-wire connection.

D

Damaged harness. Inspect the wiring harness for
damage.  If the harness is not damaged, observe an
affected sensor’s displayed value on the Tech 2 with
the ignition “ON” and the engine “OFF” while you move
the connectors and the wiring harnesses related to the
following sensors:

D

IAT

D

ECT

D

TP

D

MAP

D

EGR

D

TFT

Multiple PCM Information Sensor DTCs Set

 

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to 

Step 2

Go to 

OBD

System

Check

2

1. Turn the ignition “OFF,” disconnect the PCM.
2. Turn the ignition “ON,” check the 5 volt reference A

circuit for the following conditions:

D

A poor connection at the PCM.

D

An open between the PCM connector and the
splice.

D

A short to ground.

D

A short to voltage.

Is there an open or short?

—

Go to 

Step 3

Go to 

Step 4

3

Repair the open or short.

Is the action complete?

—

Verify repair

—

4

Check the sensor ground circuit for the following
conditions:

D

A poor connection at the PCM or the affected
sensors.

D

An open between the PCM connector and the
affected sensors.

Is there an open or a poor connection?

—

Go to 

Step 5

Go to 

Step 6

5

Repair the open or the poor connection.

Is the action complete?

—

Verify repair

—

6

Measure the voltage between the EGR pintle position
sensor signal circuit at the PCM harness connector and
ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 7

Go to 

Step 12

7

Measure the voltage between the MAP sensor signal
circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 8

Go to 

Step 15

8

Measure the voltage between the TP sensor signal
circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 9

Go to 

Step 16

9

Measure the voltage between the IAT sensor signal
circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 10

Go to 

Step 17

10

Measure the voltage between the ECT sensor signal
circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 11

Go to 

Step 18

6E–67

ENGINE DRIVEABILITY AND EMISSIONS

Multiple PCM Information Sensor DTCs Set

  (Cont'd)

Step

No

Yes

Value(s)

Action

11

1. Disconnect the EGR valve.
2. Measure the voltage between the EGR pintle

position sensor signal circuit at the PCM harness
connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 13

Go to 

Step 18

12

Measure the voltage between the TFT sensor signal
circuit at the PCM harness connector and ground.

Does the voltage measure near the specified value?

0 V

Go to 

Step 20

Go to 

Step 19

13

Replace the EGR valve.

Is the action complete?

—

Verify repair

—

14

Locate and repair the short to voltage in the MAP
sensor signal circuit.

Is the action complete?

—

Verify repair

—

15

Locate and repair the short to voltage in the TP sensor
signal circuit.

Is the action complete?

—

Verify repair

—

16

Locate and repair the short to voltage in the IAT sensor
signal circuit.

Is the action complete?

—

Verify repair

—

17

Locate and repair the short to voltage in the ECT
sensor signal circuit.

Is the action complete?

—

Verify repair

—

18

Locate and repair the short to voltage in the EGR pintle
position sensor signal circuit.

Is the action complete?

—

Verify repair

—

19

Locate and repair the short to voltage in the TFT sensor
signal circuit.

Is the action complete?

—

Verify repair

—

20

Replace the PCM.

IMPORTANT: The replacement PCM must be
programmed.  Refer to 

UBS 98model year Immobilizer

Workshop Manual.

Is the action complete?

—

Go to 

OBD

System

Check

—

6E–68

ENGINE DRIVEABILITY AND EMISSIONS

Exhaust Gas Recirculation (EGR)

Diagnosis (For except EXPORT and

SOUTH AFRICA)

Pintle position error diagnosis is covered by DTC P0402,
P0404, P1404, P0405, P0406. If EGR diagnostic trouble
codes P0402, P0404, P1404, P0405, P0406 are
encountered, refer to the DTC charts.

Engine Tech 2 Data Definitions and

Ranges

A/C CLUTCH – Tech 2 Displays ON or OFF –
Indicates whether the PCM has commanded the A/C
clutch ON.  Used in A/C system diagnostic.

A/C REQUEST — Tech 2 Displays YES or NO —
Indicates the state of the A/C request input circuit from the
HVAC controls.  The PCM uses the A/C request signal to
determine whether A/C compressor operation is being
requested.

AIR/FUEL RATIO — Tech 2 Range 0.0-25.5 —
Air/fuel ratio indicates the PCM commanded value.  In
closed loop, the air/fuel ratio should normally be
displayed around “14.2-14.7.”  A lower air/fuel ratio
indicates a richer commanded mixture, which may be
seen during power enrichment or TWC protection modes.
A higher air/fuel ratio indicates a leaner commanded
mixture.  This can be seen during deceleration fuel mode.

BAROMETRIC PRESSURE — Tech 2 Range 10-105
kPa/0.00-5.00 Volts —
The barometric pressure reading is determined from the
MAP sensor signal monitored during key up and wide
open throttle (WOT) conditions.  The barometric pressure
is used to compensate for altitude differences and is
normally displayed around “61-104” depending on
altitude and barometric pressure.

CHECK TRANS LAMP — AUTO TRANSMISSION —
Indicates the need to check for a DTC with the Tech 2
when the lamp is flashing 0.2 seconds ON and 0.2
seconds OFF.

CMP ACT. COUNTER – Cam Position Activity
DECEL FUEL MODE — Tech 2 Display ACTIVE or
INACTIVE —
“ACTIVE” displayed indicates that the PCM has detected
conditions appropriate to operate in deceleration fuel
mode.  The PCM will command the deceleration fuel
mode when it detects a closed throttle position while the
vehicle is traveling over 20 mph.  While in the deceleration
fuel delivered by entering open loop and decreasing the
injector pulse width.

DESIRED EGR POS. — Tech 2 Range 0%-100% —
Represents the EGR pintle position that the PCM is
commanding.

DESIRED IDLE — Tech 2 Range 0-3187 RPM —
The idle speed that the PCM is commanding.  The PCM
will compensate for various engine loads based on engine
coolant temperature,  to keep the engine at the desired
speed.

ECT — (Engine Coolant Temperature) Tech 2
Range –40

°

C to 151

°

C (–40

°

F to 304

°

F) —

The engine coolant temperature (ECT) is mounted in the
coolant stream and sends engine temperature
information to the PCM.  The PCM applies 5 volts to the
ECT sensor circuit.  The sensor is a thermistor which
changes internal resistance as temperature changes.
When the sensor is cold (high resistance), the PCM
monitors a high signal voltage and interprets that as a cold
engine.  As the sensor warms (decreasing resistance),
the voltage signal will decrease and the PCM will interpret
the lower voltage as a warm engine.

EGR DUTY CYCLE — Tech 2 Range 0%-100% —
Represents the EGR valve driver PWM signal from the
PCM.  A duty cycle of 0% indicates that no EGR flow is
being commanded; a 100% duty cycle indicates
maximum EGR flow commanded.

EGR FEEDBACK — Tech 2 Range 0.00-5.00 Volts —
Indicates the EGR pintle position sensor signal voltage
being monitored by the PCM.  A low voltage indicates a
fully extended pintle (closed valve); a voltage near 5 volts
indicates a retracted pintle (open valve).

ENGINE LOAD — Tech 2 Range 0%-100% —
Engine load is calculated by the PCM from engine speed
and MAF sensor readings.  Engine load should increase
with an increase in RPM or air flow.

ENGINE RUN TIME — Tech 2 Range
00:00:00-99:99:99 Hrs:Min:Sec —
Indicates the time elapsed since the engine was started.
If the engine is stopped, engine run time will be reset to
00:00:00.

ENGINE SPEED — Range 0-9999 RPM —
Engine speed is computed by the PCM from the 58X
reference input.  It should remain close to desired idle
under various engine loads with engine idling.

FUEL PUMP — Tech 2 Displays ON or OFF —
Indicates the PCM commanded state of the fuel pump
relay driver circuit.

FUEL TRIM CELL — Tech 2 Range 0-21 —
The fuel trim cell is dependent upon engine speed and
MAF sensor readings.  A plot of RPM vs.  MAF is divided
into 22 cells. Fuel trim cell indicates which cell is currently
active.

FUEL TRIM LEARN — Tech 2 Displays NO or YES
—
When conditions are appropriate for enabling long term
fuel trim corrections, fuel trim learn will display “YES.”
This indicates that the long term fuel trim is responding to
the short term fuel trim.  If the fuel trim learn displays
“NO,” then long term fuel trim will not respond to changes
in short term fuel trim.

HO2S BANK 1, SEN. 1 — Tech 2 Range 0-1132 mV
—
 Represents the fuel control exhaust oxygen sensor
output voltage.  Should fluctuate constantly within a range
between 10 mV (lean exhaust) and 1000 mV (rich
exhaust) while operating in closed loop.