check engine ISUZU TROOPER 1995 Workshop 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.

/
6E2-64 DRIVEABILITY AND EMISSIONS
Circuit Description:
DIAGNOSTIC TROUBLE CODE (DTC) 21A
THROTTLE POSITION (TP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH)
The Throttle Position (TP) Sensor provides a voltage signal that changes relative to the throttle body position.
Signal voltage
will vary from less than 1.25 volts at idle to about 5 volts at wide open throttle.
The
TP sensor signal is one of the most important inputs used by the Engine Control Module (ECM) for fuel control
and
for many of the ECM controlled outputs.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
condition.
A
DTC 21 A will set if.
• TP sensor reading above 4.6 volts.
• Engine speed less than 1200 revolution per minute.
• Manifold absolute pressure reading below 50 kPa.
• All of the above conditions are present for 2.3 seconds.
® This step simulates conditions for a DTC 21 B. If the ECM recognizes the change of state, the ECM and BLU/
ORG and BLU/RED are OK.
® This step isolates a faulty sensor, ECM, or an open BLK/WHTwire. If the BLK/WHTis open, there may also be
a
DTC 23A.
Diagnostic Aids:
A "Scan tool" displays throttle position in volts. Closed throttle voltage should be less than 1.25 volts. TP sensor ~
voltage should increase at a steady rate as throttle is moved to wide open throttle.
A
DTC 21Awill result in BLK/WHTwire is open or BLU/RED is shorted to voltage. If DTC 21A is intermittent, refer to
Section "8".
THROTILE
POSITION
SENSOR
WOT',
IDLE"' ENGINE
HARNESS
CONNECTOR
(GREEN) TO MAP
TOIAT SENSOR SENSOR
TRANSMISSION~ BLK/WHT CONTROL ~-
MODULE
(TCM)
~ GRY/BLK -----.J TERMINALS ~
Fig. 6E2-37
ENGINE CONTROL
MODULE(ECM)
SENSOR
-GROUND
•

®
DRIVEABILITY AND EMISSIONS 6E2-65
DIAGNOSTIC TROUBLE CODE (DTC) 21A
THROTILE POSITION (TP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH)
• KEY "ON" ENGINE "OFF". • THROTTLE CLOSED.
DOES "SCAN TOOL" DISPLAY THROTTLE POSITION
(TP) SENSOR OVER 2.5 VOLTS?
$ $
• DISCONNECT SENSOR, "SCAN TOOL" SHOULD • THROTTLE AT WIDE OPEN POSITION. DOES SCAN
DISPLAY TP SENSOR BELOW .2 VOLT (200mV}. TOOL DISPLAY TP SENSOR AT 4.0 VOLTS OR
DOES IT? MORE?
I
$ cvr
REFER TO DIAGNOSTIC DTC 21 IS
INTERMITTENT.
TROUBLE CODE (DTC} IF NO ADDITIONAL DTC(S} 21 B WERE STORED, REFER TO
"DIAGNOSTIC AIDS" ON FACING~.
~ $
• PROBE SENSOR GROUND CIRCUIT TP SENSOR SIGNAL CKT SHORTED TO VOLTAGE
WITH A TEST LIGHT CONNECTED TO OR BATTERY POSITIVE VOLTAGE. FAULTY ENGINE CONTROL MODULE.
I LIGHT "ON" I LIGHT "OFF" I
I FAULTY CONNECTION
OPEN SENSOR GROUND CIRCUIT OR
OR SENSOR. FAULTY ENGINE CONTROL MODULE.
CLEAR DTC(S}
AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

6E2-66 DRIVEABILITV AND EMISSIONS
DIAGNOSTIC TROUBLE CODE (DTC) 21 8
THROTILE POSITION (TP) SENSOR CIRCUIT
(SIGNAL VOLTAGE LOW)
Circuit Description:
The Throttle Position (TP) Sensor provides a voltage signal that changes relative to the throttle body position.
Signal voltage will vary from less than 1.0 volts at idle to about 5 volts at wide open throttle.
The
TP sensor signal is one of the most important inputs used by the Engine Control Module (ECM) for fuel control
and
for many of the ECM controlled outputs.
Test Description:
Numbers below refer to circled numbers on the diagnostic chart.
CD This checks to see if Diagnostic Trouble Code (DTC) 21 B is the result of a hard failure or an intermittent
condition.
A
DTC 21 B will set if:
• The engine is running
• TP sensor voltage is below .20 volts (200mV).
® This step simulates conditions for a DTC 21 A. If a DTC 21 A is set, or the "Scan tool" displays over 4 volts, the
ECM and wiring are OK.
® The "Scan tool" may not display 12 volts. The important thing is thatthe ECM recognizes the voltage as over 4
volts, indicating that BLU/RED wire and the ECM are OK.
@ If the 5 volt reference wire is open or shorted to ground, there may also be a stored DTC 338.
Diagnostic Aids:
A "Scan tool" displays throttle position in volts. Closed throttle voltage should be less than 1.0 volts. TP sensor
voltage should increase at
a steady rate as throttle is moved to wide open throttle. ~
An open or grounded BLU/ORG or BLUIRED wire will result in a DTC 21 B. If DTC 21 B is intermittent, refer to
Section "8".
THROTTLE POSITION
SENSOR ENGINE
HARNESS
CONNECTOR
WOT',
IDLE"'
(GREEN) TO MAP
TOIAT SENSOR SENSOR
TRANSMISSION~ BLK/WHT CONTROL ~ MODULE
(TCM) IC91-C6'-GRY/BLK -----..J TERMINALS ~ -
Fig. 6E2-38
ENGINE
CONTROL
MODULE(ECMl
1---..JW--5 VOLT REF
TPS SIGNAL INPUT
SENSOR
- GROUND
•

Q)
DRIVEABILITV AND EMISSIONS 6E2-67
DIAGNOSTIC TROUBLE CODE (DTC) 21 B
THROTTLE POSITION (TP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE LOW)
• THROTTLE CLOSED.
DOES "SCAN TOOL" DISPLAY THROTTLE POSITION (TP) SENSOR 0.2V· (200mV) OR BELOW?
~ $
• DISCONNECT TP SENSOR. • IF TP SENSOR
SIGNAL VOLTAGE INDICATES "HIGH" JUMPER 5V REFERENCE AND TP SENSOR SIGNAL VOLTAGE
ABOVE 4.0 VOLTS, REFER TO DIAGNOSTIC CKT TOGETHER. TROUBLE CODE 21A. "SCAN TOOL" SHOULD DISPLAY TP SENSOR OVER • DIAGNOSTIC TROUBLE CODE 21 IS INTERMITTENT.
4.0V IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES
DOES IT? WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING~.
LfJ ~
• PROBE TP SENSOR SIGNAL CKT WITH A TEST @ • REFER To FACING EAe'E'1oR J LIGHT CONNECTED TO BATTERY POSITIVE SPECIFIC INSTRUCTIONS.
VOLTAGE.
"SCAN TOOL" SHOULD DISPLAY TP SENSOR
OVER 4.0V
DOES
IT?
~ $
5V REFERENCE CKT OPEN OR SHORTED TO GROUND TP SENSOR SIGNAL CKT OPEN OR
OR SHORTED TO GROUND, OR SHORTED FAULTY CONNECTION
TO SENSOR GROUND CIRCUIT OR
OR FAULTY ENGINE CONTROL MODULE. FAULTY ENGINE CONTROL MODULE CONNECTION OR FAULTY ENGINE CONTROL MODULE.
CLEAR
DIAGNOSTIC TROUBLE CODES 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

DRIVEABILITV AND EMISSIONS 6E2-69
DIAGNOSTIC TROUBLE CODE (DTC) 23A
INTAKE AIR TEMPERATURE (IAT) SENSOR CIRCUIT
(LOW
TEMPERATURE INDICATED)
DOES "SCAN TOOL" DISPLAY INTAKE AIR TEMPERATURE -30"C OR COLDER?
@ • DISCONNECT SENSOR.
• JUMPER HARNESS TERMINALS TOGETHER. • "SCAN TOOL" SHOULD DISPLAY TEMPERATURE OVER 140"C.
DOES IT?
FAULTY CONNECTION OR SENSOR.
I
• DOES "SCAN TOOL" DISPLAY INTAKE AIR TEMPERATURE 150"C OR MORE?
DIAGNOSTIC
TROUBLE CODE (DTC) 23A IS
INTERMITTENT. IF NO ADDITIONAL
DTC(S) WERE STORED, REFER TO
"DIAGNOSTIC AIDS" ON FACING~-
@ • JUMPER 5V REFERENCE CKT TO GROUND. • "SCAN TOOL" SHOULD DISPLAY TEMPERATURE OVER 140"C.
DOES IT?
OPEN SENSOR
GROUND CIRCUIT,
FAULTY CONNECTION OR FAULTY ENGINE
CONTROL MODULE.
OPEN 5V REFERENCE CKT FAULTY CONNECTION OR FAULTY ENGINE
CONTROL MODULE.
/~ i
CLEAR DTC(S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.