1995 ISUZU TROOPER Workshop Manual

®
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.

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