1995 ISUZU TROOPER Workshop Manual

DRIVEABILITY AND EMISSIONS 6E2-73
DIAGNOSTIC TROUBLE CODE (DTC) 24
VEHICLE SPEED SENSOR (VSS) CIRCUIT
DISREGARD DIAGNOSTIC TROUBLE CODE 24
IF SET WHILE DRIVE WHEELS ARE NOT TURNING.
• VERIFY SPEEDOMETER IS WORKING, IF NOT, REFER TO SECTION 8 FOR NECESSARY REPAIR PROCEDURES. • CLEAR DIAGNOSTIC TROUBLE CODE (DTC) FROM ENGINE CONTROL MODULE (ECM) AND RETEST. IF DIAGNOSTIC TROUBLE CODE RESETS, PROCEED WITH DTC 24 CHART.
CD • RAISE DRIVE WHEELS • WITH ENGINE IDLING IN GEAR, "SCAN TOOL" SHOULD DISPLAY VEHICLE SPEED ABOVE 0. DOES IT?
$ ~
DOES SPEEDOMETER WORK? I DTC 24 IS INTERMITIENT. IF NO ADDITIONAL DIAGNOSTIC TROUBLE CODES WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING~.
CfJ ~ USING A DVOM, BACKPROBE CHECK FOR OPEN IN WHITE WIRE A ECM
ECM TERMINAL "D8" WITH DRIVE TERMINAL "D8". WHEELS ROTATING. IF OK REPLACE ECM. VOLTAGE SHOULD BE VARYING. IS IT?
$ ~ OPEN IN WHITE WIRE OR POOR CONNECTION AT ECM FAULTY SPEEDOMETER AND/OR OR SPEEDOMETER WIRING CIRCUIT FAULTY ECM
CLEAR DTC(S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.
-~---

6E2-74 DRIVEABILITY AND EMISSIONS
Circuit
Description:
DIAGNOSTIC TROUBLE CODE (DTC) 32
EXHAUST GAS RECIRCULA TION(EGR) CIRCUIT
Exhaust Gas Recirculation (EGR) valve operation is Engine Control Module (ECM) controlled. The ECM will ground
the vacuum switch
valve (VSV) to turn the EGR valve "ON" and "OFF". An EGR Back Pressure Transducer
determines how
long the EGR valve stays "ON" based on Exhaust Back Pressure supplied to the Transducer thru
Tube
"S". The ECM monitors the Integrator to determine it the EGR system is functioning. The ECM will command
the
EGR valve "OFF" briefly when the EGR is suppose to be "ON", the Integrator will change at leastthree (3) counts
indicating the
EGR valve did "close" when commanded. The ECM will then recheck the system again by
commanding
EGR valve "ON" when it should not be "ON" and again monitors the Integrator for at least a three (3)
counts change indicating the EGR valve did come "ON" when commanded. If the EGR system fails this test five (5)
times a malfunction diagnostic trouble code 32 will be logged and the malfunction indicator lamp will be "ON".
Test Description: Number(s) below refer to circled ® Check operation of ECM circuit to EGR valve VSV.
number(s} on the diagnostic chart. The EGR valva chart is a check of the EGR system. If the
CD Checks the EGR valve will open and EGR passage EGR system works properly, check other items that
is not restricted. could result in high Block Learn valve. The EGR valve
® Check that EGR valve VSV is operating properly. passage being slightly restricted may cause diagnostic
® Checks the EGR Back Pressure Transducer oper-trouble code 32 to set.
ation.
• A sluggish Heated Oxygen Sensor may also cause
@ Test voltage source as well to EGR valve VSV. this diagnostic trouble code to be set falsely.
@ Check EGR Back Pressure Transducer for proper
operation.
EGR VALVE EGRV
~
BACK
PRESSURE
TRANSDUCER
vsv
~ EGRVALVE VACUUM SWITCHING
VALVE (VSV)
ENGINE HARNESS
CONNECTOR
'+--+-' (BLU) WHT
GRN AS
f fl "'I" ___.. TO IGN PORTED VACUUM
Fig. 6E2-42
ENGINE HARNESS
CONNECTOR
(BLU)
ENGINE CONTROL
MODULE(ECM)
EGR VALVE VSV DRIVER
•

DRIVEABILITV AND EMISSIONS 6E2-75
DIAGNOSTIC TROUBLE CODE (DTC) 32
EXHAUST GAS RECIRCULATION(EGR) CIRCUIT
• FIRMLY GRASP TOP OF EXHAUST GAS RECIRCULATION (EGR} VALVE AND CHECK FOR LOOSENESS BY TRYING TO
ROTATE VALVE IN BOTH DIRECTIONS.
IS LOOSENESS FELT?
l
$
-[$J
• PLACE TRANSMISSION IN "PARK" OR "NEUTRAL". REPLACE EGR VALVE I • RUN WARM ENGINE AT IDLE. ASSEMBLY
• ENGINE TEMPERATURE MUST BE ABOVE 60'C (120'F). • DISCONNECT VACUUM HOSE TO EGR VALVE. • APPLY 10"1NCHES OF VACUUM TO EGR VALVE. • ENGINE SHOULD RUN ROUGH AND/OR STALL.
DOES IT?
I
$ $
•
CONNECT VACUUM GAGE TO EGR SIDE OF VACUUM • REMOVE EGR VALVE AND CLEAN SWITCHING VALVE (VSV). ASSEMBLY.
• INCREASE ENGINE SPEED ABOVE 2000 REVOLUTION • REPLACE
VALVE IF NECESSARY. PER MINUTE.
SHOULD HAVE AT LEAST 10 INCHES OF VACUUM. DOES IT!
I
$ $
• DATA LINK CONNECTOR GROUNDED . @ • INSTALL VACUUM GAUGE TO THE
• ENGINE IDLING CHECK VACUUM SOURCE VACUUM HOSE AT THE EGR VALVE. BEFORE EGR MODULATOR. • INCREASE ENGINE SPEED TO ABOVE 2000 . SHOULD HAVE AT LEAST 10" OF VACUUM. AT LEAST 10" OF VACUUM. DOES IT? DOES IT!
I
I
$ $ $ ~
REFER TO @ • IGNITION "ON", ENGINE "OFF". EGR SYSTEM • INSPECT BACK PRESSURE
"DIAGNOSTIC • TEST LIGHT TO GROUND. WORKING PROPERLY. TUBE "S" FOR DAMAGE OR AIDS" ON
.
• BACKPROBE VOLTAGE SOURCE NO
TROUBLE FOUND. RESTRICTION. FACING'¢{ TO EGR VALVE VSV
SOLENOID. •
INSPECT VACUUM HOSE
TEST LIGHT SHOULD BE "ON". FROM THE EGR
IS IT? MODULATOR TO THE EGR
I VALVE FOR DAMAGE OR
$ $
RESTRICTION. IF OK, REPLACE EGR MODULATOR.
@ • REPEAT ABOVE TEST WITH TEST
OPEN IN I LIGHT TO BATTERY POSITIVE CIRCUIT VOLTAGE.
• BACKPROBE EGR VALVE VSV
SOLENOID ENGINE
CONTROL MODULE CIRCUIT.
TEST LIGHT SHOULD
BE "ON". IS IT?
I
$ $
RESTRICTED VACUUM SOURCE OPEN
IN CIRCUIT OR OR FAULTY SOLENOID FAULTY ENGINE
CONTROL MODULE

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

CD
®
DRIVEABILITY AND EMISSIONS 6E2-77
DIAGNOSTIC TROUBLE CODE (DTC) 33A
MANIFOLD ABSOLUTE PRESSURE (MAP) SENSOR CIRCUIT
(SIGNAL
VOLTAGE HIGH-LOW VACUUM)
• IF ENGINE IDLE IS ROUGH, UNSTABLE, OR INCORRECT, CORRECT CONDITION BEFORE USING CHART. SEE "SYMPTOMS" IN SECTION "B". • ENGINE IDLING
• DOES "SCAN TOOL" DISPLAY A MANIFOLD ABSOLUTE PRESSURE (MAP)
VOLTAGE OF 4.0 VOLTS OR OVER?
~ $
• IGNITION "OFF". •
DOES "SCAN TOOL" DISPLAY
• DISCONNECT MAP SENSOR ELECTRICAL CONNECTOR. MAP SENSOR VOLTAGE LESS
• IGNITION "ON". THAN 1 VOLT? • "SCAN TOOL" SHOULD READ A VOLTAGE OF 1 VOLTS I OR LESS.
DOES IT?
$ $
DIAGNOSTIC TROUBLE
CODE l REFER TO J (DTC) 33A DTC
33B CHART. IS INTERMITTENT. IF NO ADDITIONAL DTC(S) WERE STORED, REFER TO "DIAGNOSTIC AIDS" ON FACING ~-
~ $
• PROBE SENSOR GROUND CIRCUIT WITH MAP SIGNAL CKT SHORTED TO A TEST LIGHT TO BATTERY POSITIVE VOLTAGE,
SHORTED TO 5 VOLT
VOLTAGE. REFERENCE CKT, OR FAULTY • TEST LIGHT SHOULD LIGHT. ENGINE CONTROL MODULE.
DOES IT?
$ $
PLUGGED OR LEAKING OPEN SENSOR GROUND CIRCUIT.
SENSOR VACUUM HOSE OR FAULTY MAP SENSOR.
CLEAR DTC(S) AND CONFIRM "CLOSED LOOP" OPERATION AND NORMAL "CHECK ENGINE" MALFUNCTION INDICATOR LAMP OPERATION.

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
..