coolant ISUZU TROOPER 1995 Repair Manual

6E2-60 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 14A
ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT
(HIGH
TEMPERATURE INDICATED)
Circuit Description:
The Engine Coolant Temperature Sensor uses a thermistor to control the signal voltage to the Engine Control
Module
(ECM). The ECM applies a reference voltage on GRY I 8LK wire to the sensor. When the engine is cold, the
sensor (thermistor) resistance is high. The
ECM will then sense a high signal voltage.
As the engine warms, the sensor resistance decreases, and the voltage drops. At normal engine operating
temperature, the
voltage will measure about 1.5 to 2.0 volts at the ECM terminal "D12."
Engine coolant temperature is one of the inputs used to control the following:
• Fuel delivery
• Ignition control
• Idle
Air Control
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD Checks to see if Diagnostic Trouble Code (DTC) was set as result of hard failure or intermittent condition.
DTC 14A will set if:
• The engine has been running for at least 3 minutes.
• Signal Voltage indicates a engine coolant temperature above 15o•c (302.F).
® This test simulates conditions for DTC 148. lfthe ECM recognizes the open circuit (high voltage), and displays
a low temperature, the ECM and wiring are OK.
Diagnostic Aids:
A "Scan tool" reads engine temperature in degrees Celsius.
After the engine is started, the temperature should rise steadily to about so·c, then stabilize, when the thermostat
opens.
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant temperature and
Intake Air Temperature (IAT) may be checked with a "Scan tool" and should read close to each other.
When a
DTC 14A is set, the ECM will turn "ON" the engine cooling fan.
A
DTC 14A will result if GRY /8LK wire is shorted to ground.
If DTC 14A is intermittent, refer to Section "8".
ENGINE
COOLANT
TEMPERATURE SENSOR. (LOCATED AT REAR OF ENGINE
BELOW
INTAKE
MANIFOLD
ASSEMBLY) ENGINE
HARNESS CONNECTOR(GREEN) L----------<~---GRY/BLK ENGINE HARNESS
CONNECTOR (GRN)
L__ ___ T_O~M(~A-P-~-~-------GRY
SENSOR
NOTICE: IT
MAY BE NECESSARY TO REMOVE THE INTAKE
MANIFOLD TO ACCESS COOLANT SENSOR ON DOHC ENGINE.
Fig. 6E2-35
ENGINE CONTROL MODULE(ECM)
ECT SENSOR SIGNAL
SENSOR GROUND
•

DRIVEABILITV AND EMISSIONS 6E2-61
DIAGNOSTIC TROUBLE CODE (DTC) 14A
ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT
(HIGH TEMPERATURE INDICATED)
(D DOES •scAN TOOL• DISPLAY ENGINE COOLANT TEMPERATURE (ECT) OF 150"C OR HIGHER?
@ • DISCONNECT SENSOR. ·sCAN TOOL • SHOULD DISPLAY TEMPERATURE BELOW -3s•c. DOES IT?
DIAGNOSTIC TROUBLE CODE 141S INTERMITTENT. IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING fA81:.
ECT SENSOR SIGNAL SHORTED TO GROUND, OR ECT SENSOR SIGNAL SHORTED TO SENSOR GROUND CIRCUIT OR FAULTY ENGINE CONTROL MODULE.
CLEAR DIAGNOSTIC TROUBLE CODES AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

6E2~62 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 148
ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
Circuit Description:
The Engine Coolant Temperature Sensor uses a thermistor to control the signal voltage to the Engine Control
Module (ECM). The ECM applies a reference voltage on GRY I 8LK wire to the sensor. When the engine is cold, the
sensor (thermistor) resistance
is high. The ECM will then sense a high Engine Coolant Temperature (ECT) sensor
signal
voltage.
As the engine warms, the sensor resistance becomes less, and the ECT sensor signal voltage drops. At normal
engine operating temperature, the voltage will measure about 1.5 to 2.0 volts at the ECM terminal "012."
ECT is one of the inputs used to control:
• Fuel delivery
• Ignition control
• Idle
Air Control
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD Checks to see if Diagnostic Trouble Code (DTC) was set as result of hard failure or intermittent condition.
DTC 148 will set if:
• The engine has been running at least for 3 minutes.
• ECT sensor signal voltage indicates a ECT above -35°C (-31 OF) for 30 seconds.
® This test simulates conditions for DTC 14A. If the ECM recognizes the grounded circuit (low voltage), and
displays a high temperature, the ECM and wiring are OK.
@ This test will determine if there is a wiring problem or a faulty ECM.
Diagnostic Aids:
A "Scan tool" reads engine temperature in degrees Celsius.
After the engine is started, the temperature should rise steadily to about 90°C, then stabilize, when the thermostat
opens.
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and intake air
temperature may be checked
with a "Scan tool" and should read close to each other.
A
DTC 148 will result if GRY/8LK wire GRY are open.
If DTC 148 is intermittent, refer to Section "8".
ENGINE
COOLANT
TEMPERATURE SENSOR.
(LOCATED AT REAR OF ENGINE
BELOW
INTAKE
MANIFOLD
ASSEMBLY) ENGINE
HARNESS
CONNECTOR (GREEN) c__---------<~'----GRY/BLK ENGINE HARNESS
CONNECTOR (GRN)
~---T-0--<'M<(--A-P_J ___________ GRY
SENSOR
Fig. 6E2-36
ENGINE CONTROL MODULE(ECM)
ECT
SENSOR SIGNAL
SENSOR GROUND
•

®
DRIVEABILITV AND EMISSIONS 6E2-63
DIAGNOSTIC TROUBLE CODE (DTC) 148
ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
FROM DIAGNOSTIC
TROUBLE CODE CHART 14A
I • DOES "SCAN TOOL" DISPLAY ENGINE COOLANT TEMPERATURE OF -35"l OR LESS?
I
~ $
• DISCONNECT SENSOR. DTC 14 IS INTERMITTENT. JUMPER
HARNESS TERMINALS TOGETHER. IF NO ADDITIONAL DTC(S) WERE STORED, REFER TO
• "SCAN TOOL" SHOULD DISPLAY 150" OR MORE. "DIAGNOSTIC AIDS" ON FACING~ DOES IT?
I
$ c$
• JUMPER
GRY WIRE TO GROUND. FAUL TV CONNECTION OR SENSOR. I • "SCAN TOOL" SHOULD DISPLAY OVER 150"C.
DOES IT?
I
~ $
OPEN SENSOR GROUND OPEN IN GREY WIRE,
CIRCUIT, FAUL TV CONNECTION FAUL TV CONNECTION AT OR FAUL TV ENGINE CONTROL ENGINE CONTROL MODULE,
MODULE. OR FAUL TV ECM.
CLEAR DTC(S)
AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

6E2-68 DRIVEABILITV AND EMISSIONS
DIAGNOSTIC TROUBLEL CODE (DTC) 23A
INTAKE AIR TEMPERATURE {IAT) SENSOR CIRCUIT
(LOW TEMPERATURE INDICATED)
Circuit Description:
The Intake Air Temperature (IAT) Sensor uses a thermistor to control the signal voltage to the Engine Control
Module
(ECM). The ECM applies a voltage (4-6volts) to BLU/BLK wire of the sensor. When manifold air is cold, the
sensor (thermistor) resistance is high, therefore, the
ECM will see a IAT signal. As the air warms, the sensor
resistance becomes
less and the IAT signal drops.
IAT LOW Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD This step checks to see if Diagnostic Trouble Code (DTC) 23A is the result of a hard failure or an intermittent
condition.
A
DTC 23A will set if:
• Signal voltage indicates a IAT temperature less than -30"C
• Engine has been running for longer than 3 minutes.
® This test simulates conditions for DTC 238. If the "Scan tool" displays a high temperature, the ECM and wiring
are OK.
@ This step checks continuity of BLU/BLK and BLK/WHT wires. If BLK/WHT wire is open there may also be a
DTC 21A.
Diagnostic Aids:
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and IAT may be
checked
with a "Scan tool" and should read nearly the same. ~
A DTC 23A will result if BLU/BLK or BLK/WHT wires become open.
If DTC 23A is intermittent, refer to Section "6E2-B".
INTAKE AIR TEMPERATURE SENSOR
ENGINE HARNESS
CONNECTOR
(GREEN) I
L-----------«----BLU/BLK
TO TPS
Fig. 6E2-39
ENGINE CONTROL
MODULE(ECM)
IATSIGNAL
1--'--IW'--5V REF
SENSOR GROUND

6E2-70 DRIVEABILITV AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 238
INTAKE AIR TEMPERATURE (IAT) SENSOR CIRCUIT
(HIGH
TEMPERATURE INDICATED)
Circuit Description:
The Intake Air Temperature (IAT) Sensor uses a thermistor to control the signal voltage to the Engine Control
Module (ECM). The
ECM applies a voltage (4-6 volts) to 8LU/8LK wire ofthe sensor. When manifold air is cold, the
sensor (thermistor) resistance is high, therefore, the
ECM will see a IAT signal. As the air warms, the sensor
resistance becomes less and the
IAT signal drops.
IAT HIGH Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD This check determines if the Diagnostic Trouble Code (DTC) 238 is the result of a hard failure or an
intermittent condition.
A
DTC 238 will set if:
• Engine has been running for longer than 3 minutes.
• An IAT greater than 150°C is detected.
Diagnostic Aids:
If the engine has been allowed to cool to an ambient temperature (overnight), engine coolant and IAT may be
checked with a "Scan tool" and should read nearly the same.
A
DTC 238 will result if 8LU/8LK or 8LK/WHT wires become open, or shorted to ground.
If DTC 238 is intermittent, refer to Section "6E2-8".
INTAKE AIR TEMPERATURE SENSOR
ENGINE
HARNESS CONNECTOR (GREEN) I
L-----------~;-----BLU/BLK
TO TPS
Fig. 6E2-40
ENGINE CONTROL MODULE(ECM)
IAT SIGNAL
1--J..-,JW--5V REF
SENSOR GROUND
II

6E2-76 DRIVEABILITY AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 33A
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH-LOW VACUUM)
Circuit Description:
The Manifold Absolute Pressure {MAP) Sensor responds to changes in manifold pressure (vacuum). The Engine
Control Module (ECM) receives this information as a signal voltage that will vary from about 1 to 1.5 volts, at closed
throttle idle, to 4-4.5 volts at
wide open throttle (low vacuum).
If the MAP sensor fails, the ECM will substitute a fixed MAP value based on Throttle Position Sensor to control fuel
delivery.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD This step will determine if Diagnostic Trouble Code (DTC) 33 is the result of a hard failure or an intermittent
condition.
A
DTC 33 will set if:
• MAP signal indicates greater than 95 kPa (low vacuum).
• Throttle position sensor less than 2%.
• No DTC 21 A or DTC 21 B is set.
• These conditions are present for a time longer than 5.3 seconds.
® This step simulates conditions for a DTC 338. If the ECM recognizes the change, the ECM, and BLU/ORG and
GRY /RED wires are OK. If GRY wire is open, there may also be a DTC 23 stored.
Diagnostic Aids:
With the Ignition "ON" and the engine stopped, the manifold pressure is equal to atmospheric pressure and the
signal voltage
will be high. This information is used by the ECM as an indication of vehicle altitude and is referred ~
to as barometric pressure. Comparison of this barometric pressure reading with a known good vehicle with the
same sensor is a good
way to check accuracy of a "suspect" sensor. Readings should be the same ±0.4 volt.
A
DTC 33A will result if GRY /Wire is open, or if GRY /RED is shorted to voltage or to BLU/ORG wire.
If DTC 33A is intermittent, refer to Section "6E2-B".
MANIFOLD ABSOLUTE
PRESSURE
SENSOR
TO MANIFOLD ....__ _______ __,
ABSOLUTE
PRESSURE
(VACUUM)
HARNESS ENGINE
CONNECTOR
(BLUE) TOTPS
TO ENGINE
COOLANT
TEMPERATURE SENSOR
Fig. 6E2-43
GRY
ENGINE CONTROL MODULE(ECM)
t---~W--5 VOLT REF
SENSOR
- GROUND

6E2-78 DRIVEABILITV AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 338
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE LOW-HIGH VACUUM)
Circuit Description:
The Manifold Absolute Pressure (MAP) Sensor responds to changes in manifold pressure (vacuum). The Engine
Control Module (ECM) receives this information as a signal voltage that will vary from about 0.45 to 0.85 volts, at
closed throttle idle, to 3.8-4.5 volts at Wide Open Throttle (low vacuum).
If the MAP sensor fails, the ECM will substitute a fixed MAP value based on Throttle Position Sensor to control fuel
delivery.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD This step will determine if Diagnostic Trouble Code (DTC) 338 is the result of a hard failure or an intermittent
condition.
A
DTC 338 will set if:
• Engine speed is greater than 1100 revolution per minute.
• Throttle position sensor is greater than 20%.
•
MAP signal indicates less then 10.7 kPa.
• These conditions are present for a time longer than 0.125 seconds.
• No DTC 21 A or DTC 21 8 is set.
® Jumpering harness terminals "8" to "C", 5 volt to signal, will determine if the sensor is at fault, or if there is a
problem with ECM or wiring.
® The "Scan tool" may not display 12 volts. The important thing is that the ECM recognizes the voltage as more
than 4
volts, indicating that the ECM and GAY /RED wire are OK.
Diagnostic Aids:
With the Ignition "ON" and the engine stopped, the manifold pressure is equal to atmospheric pressure and the
signal voltage will be high. This information is used by the ECM as an indication of vehicle altitude and is referred
to as barometric pressure. Comparison of this barometric pressure reading with a known good vehicle with the
same sensor is a good
way to check accuracy of a "suspect" sensor. Readings should be the same ±0.4 volt.
A DTC 338 will result if GAY /Wire is open, or if GAY /RED is shorted to voltage or to 8LUIORG wire.
If DTC 338 is intermittent, refer to Section "6E2-8".
MANIFOLD ABSOLUTE
PRESSURE SENSOR
TO MANIFOLD .._ _______ --.~
ABSOLUTE
PRESSURE
(VACUUM)
HARNESS ENGINE
CONNECTOR
(BLUE) TOTPS
TO ENGINE COOLANT TEMPERATURE SENSOR
Fig. 6E2-44
GRY
ENGINE CONTROL MODULE(ECM)
SENSOR -GROUND
..

6E2-90 DRIVEABILITY AND EMISSIONS
INTERMITTENTS
Definition: Problem may or may not turn "ON" the
"Check Engine" malfunction indicator lamp or store
Diagnostic
Trouble Code (DTC).
DO NOT use the DTC charts in "Engine Components/
Wiring Diagrams/Diagnostic
Charts," Section "6E2-A"
for intermittent problem. The fault must be present to
locate the problem. If a fault is intermittent, use of DTC
charts may result in replacement of good parts.
•
• Most intermittent problems are caused by faulty
electrical
connections or wiring. Perform careful
visual/physical
check as described at start of
"Symptoms," Section "6E2-B." Check for:
Poor mating
of the connector halves. or
terminal not fully seated in the connector body
(backed out).
Improperly formed or damaged terminal. All
connector
terminals in the problem circuit
should be carefully reformed or replaced to
insure proper contact tension.
Poor
terminal to wire connection. This
requires removing the
terminal from the
connector body to check. Refer to
SECTION 8
"Wiring Harness Service,"
If a visual/physical check does not find the cause
of the problem, the car can be driven with a
voltmeter connected to a suspected circuit. A
"Scan tool" can also be used to help detect
intermittent conditions. An abnormal
voltage, or
"Scan" tool reading, when the problem occurs,
indicates the
problem may be in that circuit. If the wiring
and connectors check
OK, and a DTC was
stored
for a circuit having a sensor, except for
DTC(s) 44 and 45, substitute a known good sensor
and recheck.
• Loss of DTC memory. To check, disconnect
throttle position (TP) sensor and idle engine until
"Check
Engine" malfunction indicator lamp comes
"ON". DTC 21 should be stored, and kept in
memory when ignition is turned "OFF". If not, the
Engine
Control Module (ECM) is faulty.
•
An intermittent "Check Engine" malfunction
indicator
lamp with no stored DTC may be caused
by:
Ignition coil shorted to ground and arcing at
spark
plug wires or plugs.
"Check
Engine" malfunction indicator lamp
wire to ECM shorted to ground.
Diagnostic
"test" terminal wire to ECM,
shorted to ground.
ECM grounds, refer to ECM wiring diagrams.
• Check for an electrical system interference caused
by a defective
relay, ECM driven solenoid, or
switch. They can cause a sharp electrical surge.
Normally, the problem will occur when the faulty
component is operated.
• Check for improper installation of electrical
options such as lights, 2 way radios, etc.
• Ignition control wires should be routed away from
spark plug wires, electronic ignition (EI) wires, El
housing, coil and generator. Ground wire from
ECM to El should have a good connection.
• If problem has not been found, refer to "ECM
Connector Symptom" charts at the end of
"Symptoms," Section "6E2-B."
HARD START
Definition: Engine cranks OK, but does not start for a
long time. Does eventually run, or may
start
but immediately dies.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B".
•
Make sure the driver is using the correct starting
procedure.
SENSORS
• CHECK: Engine coolant temperature sensor using
a
"Scan tool", compare engine coolant
temperature with ambient temperature
on
cold engine. -
If engine coolant temperature
readings
is 5 degrees greater than or less than
ambient air temperature on a
cold
engine, check resistance in engine
coolant temperature sensor circuit
or
sensor itself. Compare engine coolant
temperature sensor resistance value
to the "Diagnostic Aids" chart on
DTC
14 chart.
• CHECK: Manifold absolute pressure sensor.
Check for flooding and/or correct sensor
for vehicle.
• CHECK: TP sensor for binding or a high TP sensor
voltage with the throttle closed (should
read between 0.54 volt and 1.25 volts.)

6E2-92 DRIVEABILITY AND EMISSIONS
LACK OF POWER, SLUGGISH OR SPONGY
Definition: Engine delivers less than expected power.
Little or no increase in speed when
accelerator
pedal is pushed down part
way.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
described at start of "Symptoms," Section "6E2-
B."
•
Compare customer's car to similar unit. Make sure
the
vehicle has an actual problem.
• Remove air filter and check air filter for dirt, or for
being plugged. Replace as necessary.
FUEL SYSTEM
• CHECK: Rescricted fuel filter.
• CHECK: Fuel pressure, use CHART A-7.
• CHECK: Contaminated fuel.
• CHECK: Fuel injectors are correct for the vehicle.
IGNITION SYSTEM
• CHECK: Ignition timing, using "Scan tool".
• CHECK: Knock sensor system for excessive spark
retard activity. Refer to CHART
C-5. Use
"Scan tool".
• CHECK: Secondary voltage using an oscilloscope
or a spark tester J 26792 (ST-125), or
equivalent, to check for a weak coil.
ADDITIONAL CHECKS
• CHECK: Engine control module grounds for being
clean,
tight and in their proper locations.
See engine control module wiring
diagrams.
• CHECK: Exhaust gas recirculation operation for
being open or partly open all the time.
- Refer to CHART
C-7.
• CHECK: Generator output voltage. Repair if less
than 9
or more than 16 volts.
• CHECK: Exhaust system for possible restriction.
Refer
to CHART B-1.
-Inspect exhaust system for damaged
or collapsed pipes.
-
Inspect muffler for heat damage or
possible internal failure.
• CHECK: Torque converter clutch for proper
operation. Refer
to AUTOMATIC
TRANSMISSION
(SECTION 7A).
ENGINE MECHANICAL
• CHECK: Engine valve timing and compression.
• CHECK: Engine for correct or worn camshaft.
Refer
to ENGINE MECHANICAL
DIAGNOSIS
(SECTION 6A).
DETONATION/SPARK KNOCK
Definition: A mild to severe ping, usually worse under
acceleration. The engine makes sharp
metallic knocks that change with throttle
opening.
Sounds like popcorn popping.
PRELIMINARY CHECKS
• Perform the careful visual/physical checks as
Low engine coolant.
Restricted air
flow to radiator, or restricted
water flow through radiator.
Correct engine
coolant solution should be a 50/
50 mix of anti-freeze engine coolant (or
equivalent) and water.
described at start
of "Symptoms," Section "6E2-FUEL SYSTEM
B."
•
Park/Neutral position switch. Be sure "Scan tool"
indicates drive with gear selector in drive or
overdrive. Use
CHART C-1A.
• If "Scan tool" readings are normal (see facing page
of on-board diagnostic system check) and there
are no engine mechanical faults,
fill fuel tank with a
gasoline
that has a minimum octane reading of 87
and revaluate vehicle performance.
• CHECK: Exhaust gas recirculation system for not
opening. Use CHART C-7.
COOLING SYSTEM
• Check for obvious overheating problems:
• NOTICE: To determine if the condition is caused by
a rich
or lean system, the car should be
driven at the speed
of the complaint.
Monitoring
LT. Fuel Trim will help
identify problem.
Lean-
LT. Fuel Trim above 142. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 44.
Rich-LT. Fuel Trim below 118. Refer to
"Diagnostic Aids" on facing page of
diagnostic trouble code 45.
• CHECK: Fuel pressure, use CHART A-7.
..