sensor ISUZU TROOPER 1998 Service Repair Manual

6E±93 ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve. To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing by pass air flow. Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).
Diagnostic Aids
A slow, unstable, or fast idle may be caused by a non-IAC
system problem that cannot be overcome by the IAC
valve. Out of control range IAC Tech 2 counts will be
above 60 if idle is too low, and zero counts if idle is too
high. The following checks should be made to repair a
non-IAC system problem:

Vacuum leak (high idle) ± If idle is too high, stop the
engine. Fully extend (low) IAC with the Tech 2. Start
the engine. If idle speed is above 800 RPM, locate and
correct the vacuum leak, including the PCV system.
Check for binding of the throttle blade or linkage.

Lean heated oxygen sensor signal (high air/fuel ratio) ±
The idle speed may be too high or too low. Engine
speed may vary up and down, and disconnecting the
IAC valve does not help. Diagnostic trouble codes
P0131, P0151, P0171, or P0174 may be set. Tech 2
oxygen (O2) voltage will be less than 100 mV (0.1 V).
Check for low regulated fuel pressure, water in fuel, or
a restricted injector.

Rich heated oxygen sensor signal (low air/fuel ratio) ±
The idle speed will be too low. Tech 2 IAC counts will
usually be above 80. The system is obviously rich and
may exhibit black smoke in the exhaust.
Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V). Check for high fuel pressure, or a leaking or
sticking injector. A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on Tech 2.
Throttle body ± Remove the IAC valve and inspect the
bore for foreign material.

IAC valve electrical connections ± IAC valve
connections should be carefully checked for proper
contact.

PCV valve ± An incorrect or faulty PCV valve may
result in an incorrect idle speed. Refer to
Diagnosis,
Rough Idle, Stalling.
If intermittent poor driveability or
idle symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve terminal
resistance, or replace the IAC.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The Tech 2 is used to extend and retract the IAC
valve. Valve movement is verified by an engine
speed change. If no change in engine speed
occurs, the valve can be resettled when removed
from the throttle body.
2. This step checks the quality of the IAC movement in
step 1. Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract. If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop. This
is normal on certain engines. Fully extending the
IAC may cause engine stall. This may be normal.

6E±95 ENGINE DRIVEABILITY AND EMISSIONS
Knock Sensor (KS) System Check
(Engine Knock, Poor Performance, or Poor Economy)
D06RW035
Circuit Description
The knock sensor (KS) sends an AC voltage signal to the
powertrain control module (PCM). As the KS detects
engine knock, the signal to the PCM changes in amplitude
and frequency. The PCM retards timing if the engine
speed is over 900 RPM.
Diagnostic Aids
If the KS system checks OK, but detonation is the
complaint, refer to
Diagnosis, Detonation/Spark Knock.
Test Description
The numbers below refer to the step numbers on the
Diagnostic Chart.
9. The change in signal speed depends on how hard
the tapping is done. Normally there is about 1.5 to
10 mV at PCM pin A2 with the engine off. Loud
tapping should be able to make the reading jump to
20-25 mV AC.

6E±96
ENGINE DRIVEABILITY AND EMISSIONS
Knock Sensor (KS) System Check
(Engine Knock, Poor Performance, or Poor Economy)

StepActionValue(s)Ye sNo
1Is DTC P0325 or P0327 set?
Ð
Go to DTC
P0325 or
DTC P0327
Go to Step 2
2Run the engine at 1500 RPM.
Is there an internal engine knock?
ÐGo to Step 3Go to Step 4
3Repair the mechanical problem.
Is the action complete?
ÐVerify repairÐ
41. Install Tech 2.
2. Turn the ignition ªON.º
3. Cycle through the list until ªKnock Retardº is
displayed.
Is knock retard at the specified value?
0
Go to Step 6Go to Step 7
5Replace the PCM.
IMPORTANT:The replacement PCM must be
programmed. Refer to
UBS 98model year Immobilizer
Workshop Manual.
Is the action complete?ÐVerify repairÐ
61. Start the engine.
2. Monitor the knock retard display on Tech 2 while
changing the throttle setting to place different loads
on the engine.
Is knock retard at the specified value? (Turn the ignition
ªOFF.º)
0
Go to Step 9Go to Step 7
71. At the rear of the engine, behind the rear fuel
injector on the lift side, disconnect the 2-wire knock
sensor harness connector.
2. Attach the positive lead of DVM to B+.
3. On the main harness side of the connector, use the
negative lead of the DVM to probe the connector pin
that is connected to the black wire.
Dose the DVM indicate the specified value?
(Reconnect the knock sensor harness.)
B+Go to Step 9Go to Step 8
8Repair the open black wire ground for the shield which
prevents stray electromagnetic pulses from affecting
the knock signal.
Is the action complete?
ÐVerify repairÐ
91. Reconnect the wire harness.
2. Set a DVM to AC voltage.
3. With the DVM, backprobe the PCM connector at
A2.
4. Tap the engine lift brackprobe with a socket
extension.
Did the DVM show an increase in AC voltage while
tapping on the lift bracket?
ÐSystem OKGo to Step 10
10Replace the knock sensor.
Is the action complete?
ÐVerify repairÐ

6E±97 ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR) System Check
D06RW106
Circuit Description
A properly operation exhaust gas recirculation (EGR)
system will directly affect the air/fuel requirements of the
engine. Since the exhaust gas introduced into the air/fuel
mixture is an inert gas (contains very little or no oxygen),
less fuel is required to maintain a correct air/fuel ratio.
Introducing exhaust gas into the combustion chamber
lowers combustion temperatures and reduces the
formation of oxides of nitrogen (NOx) in the exhaust gas.
Lower combustion temperatures also prevent detonation.
If the EGR pintle were to stay closed, the inert exhaust
gas would be replaced with air and the air/fuel mixture
would be leaner. The powertrain control module (PCM)
would compensate for the lean condition by adding fuel,
resulting in higher long term fuel trim values.
Diagnostic Aids
The EGR valve chart is a check of the EGR system. An
EGR pintle constantly in the closed position could cause
detonation and high emissions of NOx. It could also result
in high long term fuel trim values in the open throttle cell,
but not in the closed throttle cell. An EGR pintle
constantly in the open position would cause a rough idle.
Also, an EGR mounted incorrectly (rotated 180
) could
cause rough idle. Check for the following items:

EGR passages ± Check for restricted or blocked EGR
passages.

Manifold absolute pressure sensor ± A manifold
absolute pressure sensor may shift in calibration
enough to affect fuel delivery. Refer to
Manifold
Absolute Pressure Output Check.

6E±99 ENGINE DRIVEABILITY AND EMISSIONS
Manifold Absolute Pressure (MAP) Output Check
D06RW102
Circuit Description
The manifold absolute pressure (MAP) sensor measures
the changes in the intake MAP which result from engine
load (intake manifold vacuum) and engine speed
changes; and converts these into a voltage output. The
powertrain control module (PCM) sends a 5-volt
reference voltage to the MAP sensor. As the MAP
changes, the output voltage of the sensor also changes.
By monitoring the the sensor output voltage, the PCM
knows the MAP. A lower pressure (low voltage) output
voltage will be about 1-2 volts at idle. Higher pressure
(high voltage) output voltage will be about 4-4.8 volts at
wide open throttle. The MAP sensor is also used, under
certain conditions, to measure barometric pressure,
allowing the PCM to make adjustments for different
altitudes. The PCM uses the MAP sensor to diagnose
proper operation of the EGR system, in addition to other
functions.
Test Description
IMPORTANT:Be sure to used the same diagnostic test
equipment for all measurements.
The number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Applying 34 kPa (10 Hg) vacuum to the MAP sensor
should cause the voltage to be 1.5-2.1 volts less
than the voltage at step 1. Upon applying vacuum
to the sensor, the change in voltage should be
instantaneous. A slow voltage change indicates a
faulty sensor.
3. Check the vacuum hose to the sensor for leaking or
restriction, Be sure that no other vacuum devices
are connected to the MAP hose.
IMPORTANT:Make sure the electrical connector
remains securely fastened.
4. Disconnect the sensor from the bracket. Twist the
sensor with your hand to check for an intermittent
connection. Output changes greater than 0.10 volt
indicate a bad sensor.

6E±100
ENGINE DRIVEABILITY AND EMISSIONS
Manifold Absolute Pressure (MAP) Output Check

StepActionValue(s)Ye sNo
11. Turn the ignition ªOFFºand leave it ªOFFº for 15
seconds.
2. Ignition ªON.º Don't crank engine.
3. Tech 2 should indicate a manifold absolute pressure
(MAP) sensor voltage.
4. Compare this scan reading to scan reading of a
known good vehicle obtained using the exact same
procedure as in Steps 1-4.
Is the voltage reading the same +/±0.40 volt?
ÐGo to Step 2Go to Step 5
21. Disconnect the vacuum hose at the MAP sensor
and plug the hose.
2. Connect a hand vacuum pump to the MAP sensor.
3. Start the engine.
4. Apply 34 kPa (10 Hg) of vacuum and note the
voltage change.
Is the voltage change 1.5-2.1 volts less than Step 1?
ÐGo to Step 3Go to Step 4
3No trouble found. Check the sensor cover for leakage
or restriction.
Does the hose supply vacuum to the MAP sensor only?
ÐGo to Step 5Go to Step 4
4Repair the material to block.
Is the action complete?
ÐVerify repairÐ
5Check the sensor connection.
Is the sensor connection good?
ÐGo to Step 6Go to Step 7
6Replace the sensor. Refer to On-Vehicle Service, MAP
Sensor.
Is the action complete?ÐVerify repairÐ
7Repair the poor connection.
Is the action complete?
ÐVerify repairÐ

6E±104
ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0101 MAF System Performance
D06RW103
Circuit Description
The mass air flow (MAF) sensor measures the amount of
air which passes through it into the engine during a given
time. The powertrain control module (PCM) uses the
mass air flow information to monitor engine operating
conditions for fuel delivery calculations. A large quantity
of air entering the engine indicates an acceleration or high
load situation, while a small quantity or air indicates
deceleration or idle.
The MAF sensor produces a frequency signal which can
be monitored using a Tech 2. DTC P0101 will be set if the
signal from the MAF sensor does not match a predicted
value based on throttle position and engine RPM.
Conditions for Setting the DTC

The engine is running.

No TP sensor or MAP sensor DTCs are set.

The throttle is steady, TP angle doesn't change by
more than 1%.

System voltage is between 11.5 volts and 16 volts.

Calculated air flow is between 25 g/second and 40
g/second.

Above conditions present for at least 1 second.

MAF signal frequency indicates an airflow significantly
higher or lower than a predicted value based on throttle
position and engine RPM for a total of 12.5 seconds
over a 25-second period of time.
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) after the second consecutive trip in which the
fault is detected.

The PCM calculates an airflow value based on idle air
control valve position, throttle position, RPM and
barometric pressure.

The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P0101 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
An intermittent may be caused by the following:

Poor connections.

Mis-routed harness.

Rubbed through wire insulation.

Broken wire inside the insulation.
Refer to Intermittents under service category Symptoms.
Any un-metered air may cause this DTC to set. Check for
the following:

The duct work at the MAF sensor for leaks.

An engine vacuum leak.

The PCV system for vacuum leaks.

An incorrect PCV valve.

6E±105 ENGINE DRIVEABILITY AND EMISSIONS

The engine oil dip stick not fully seated.

The engine oil fill cap loose or missing.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. The MAF system performance or ªrationalityº
diagnostic uses the MAP sensor signal along with
other input to calculate an expected airflow rate that
is then compared to the actual measured airflow
from the MAF sensor. The first few steps of this
table verify that the MAP sensor is working properly.
6. Using Freeze Frame and/or Failure Records data
may aid in locating an intermittent condition. If the
DTC cannot be duplicated, the information included
in the Freeze Frame and/or Failure Records data
can be useful in determining how many miles since
the DTC set. The Fail Counter and Pass Counter
can also be used to determine how many ignition
cycles the diagnostic reported a pass and/or a fail.
Operate the vehicle within the same Freeze Frame
conditions (RPM, load, vehicle speed , temperature,
etc.) that were noted. This will isolate when the
DTC failed.For any test that requires back probing the PCM or
component harness connectors, use the Connector
Test Adapter Kit J 35616-A. Using this kit will
prevent any damage to the harness connector
terminals.
7. Any un-metered air may cause this DTC to set.
Check the PVC system for vacuum leaks. Also
inspect the dip stick for being pulled out. Check the
oil fill cap for being loose.
8. Verifies the signal circuit from the MAF sensor
electrical connector to the PCM.
9. Verifies whether a ground and B+ circuit is available.
10. Checks a signal circuit for an open.
11. Checks for a signal circuit shorted to B+.
DTC P0101 ± MAF System Performance

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Ignition ªON,º engine ªOFF.º
2. Using a Tech 2, select ªMAPº from the Engine 1
Data List.
Is the value displayed greater than the value shown?
85 kPaGo to Step 3Go toStep 13
31. Remove the MAP sensor from the intake manifold
but leave the electrical harness connected.
2. Connect a hand operated vacuum pump to the MAP
sensor.
3. Observe the MAP display while slowly applying
vacuum up to 20º Hg as indicated on the pump
gauge.
Each 1º of vacuum applied should result in a 3 to 4 kPa
drop in the MAP sensor value on the Tech 2 and the
value should change smoothly with each increase in
vacuum.
Did the MAP value change smoothly through the entire
range of the test without any erratic readings?
ÐGo to Step 13Go to Step 4
4With 20º Hg vacuum applied to the MAP sensor, is the
MAF sensor reading the same or less than the value
shown?
34 kPaGo to Step 5Go to Step 13
5Disconnect the vacuum source from the MAP sensor.
Does the MAP sensor reading return to its original
value?
ÐGo to Step 6Go to Step 13

6E±106
ENGINE DRIVEABILITY AND EMISSIONS
DTC P0101 ± MAF System Performance

 
StepNo Ye s Value(s) Action
61. Ignition ªON,º engine ªOFF.º
2. Review the Freeze Frame and/or Failure Records
data for this DTC and note parameters.
3. Ignition ªOFFº for 15 seconds.
4. Start the engine and operate the vehicle within the
conditions required for this diagnostic to run, and as
close to the conditions recorded in Freeze Frame
/Failure Records possible. (Special operating
conditions that need to be met before the PCM will
run this diagnostic (where applicable) are listed in
ªConditions for Setting the DTCº).
5. Using the Tech 2, select ªDTC,º then enter the DTC
number which was set.
Does the Tech 2 indicate that this diagnostic failed this
ignition?
ÐGo to Step 7
Refer to
Diagnostic
Aids
71. Check for the following conditions:

Objects blocking the MAF sensor inlet screen;

Intake manifold vacuum leaks;

Vacuum leaks at throttle body;

Vacuum leaks EGR value flange and pipes.

Crankcase ventilation valve faulty, missing, or
incorrectly installed.
2. If a problem is found, repair as necessary.
Was a problem found?
ÐVerify repairGo toStep 8
81. Ignition ªOFF.º
2. Disconnect the MAF sensor connector.
3. Ignition ªON,º engine ªOFF.º
4. Using DVM 5-8840-0285-0, measure voltage
between the MAF sensor signal circuit and chassis
ground.
Is the voltage near the specified value?
5 VGo to Step 9Go toStep 10
9Connect a test light (5-8840-0607-0) between the MAF
sensor ignition feed and ground circuits at the MAF
sensor harness connector.
Is the test light ªON?º
ÐGo to Step 13Go toStep 12
10Is the voltage less than the specified value?4.5 VGo to Step 13Go toStep 11
111. Ignition ªOFF,º disconnect the PCM.
2. Ignition ªON,º engine ªOFF.º
3. Measure voltage between the MAF signal circuit
and ground.
Does the voltage measure near the specified value?
0 VGo to Step 13Go toStep 12
12Connect a test light (5-8840-0607-0) between the MAF
sensor ignition feed circuit and chassis ground.
Is the test light ªON?º
ÐGo to Step 13Go toStep 7
131. Check for a poor connection at the MAF sensor.
2. If a poor connection is found, replace faulty
terminal(s). Refer to
Repair Procedures in
Electrical Diagnosis (8A Cell 5).
Was a poor connection found?ÐVerify repairSolved

6E±107 ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Trouble Code (DTC) P0102 MAF Sensor Circuit Low Frequency
T321122
Circuit Description
The mass air flow (MAF) sensor measures the amount of
air which passes through it into the engine during a given
time. The powertrain control module (PCM) uses the
mass air flow information to monitor engine operating
conditions for fuel delivery calculations. A large quantity
of air entering the engine indicates an acceleration or high
load situation, while a small quantity of air indicates
deceleration or idle.
The MAF sensor produces a frequency signal which can
be monitored using a Tech 2. The frequency will vary
within a range of around 2500 Hz at idle to around
1900 Hz at maximum engine load. DTC P0102 will be set
if the signal from the MAF sensor is below the possible
range of a normally operating MAF sensor.
Conditions for Setting the DTC

The engine is running above 500 RPM for greater than
10 seconds.

System voltage is above 11.5 volts.

MAF signal frequency is below 1000 Hz for a total of
50-percent of the last 1000 samples monitored. A
sample is taken every cylinder event.
Action Taken When the DTC Sets

The PCM will illuminate the malfunction indicator lamp
(MIL) the first time the fault is detected.

The PCM calculates an air flow value based on idle air
control valve position, throttle position, RPM and
barometric pressure.
The PCM will store conditions which were present
when the DTC was set as Freeze Frame and in the
Failure Records data.
Conditions for Clearing the MIL/DTC

DTC P0102 can be cleared by using the Tech 2 ªClear
Infoº function or by disconnecting the PCM battery
feed.
Diagnostic Aids
Check for the following conditions:

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

Misrouted harness ± Inspect the MAF sensor harness
to ensure that it is not routed too close to high voltage
wires.

Damaged harness ± Inspect the wiring harness for
damage. If the harness appears to be OK, observe the
Tech 2 while moving connectors and wiring harnesses
related to the MAF sensor. A change in the display will
indicate the location of the fault.

Plugged intake air duct or filter element ± A wide-open
throttle acceleration from a stop should cause the
mass air flow displayed on a Tech 2 to increase from
about 3-6 g/second at idle to 100 g/second or greater
at the time of the 1-2 shift. If not, check for a restriction.
If DTC P0102 cannot be duplicated, the information
included in the Failure Records data can be useful in
determining vehicle mileage since the DTC was last set.