Isuzu N-Series. Manual - part 416

6D6-10 QOS II PREHEATING SYSTEM

EMISSION AND ELECTRICAL DIAGNOSIS 6E-1

ENGINE 4H SERIES

SECTION 6E (4HE1-TC/4HG1-T Only)

EMISSION AND ELECTRICAL DIAGNOSIS

Caution:
When fasteners are removed, always reinstall them at the same location from which they were removed. If a fastener
needs to be replaced, use the correct part number fastener for that application. If the correct part number fastener is
not available, a fastener of equal size and strength for (stronger) may be used. Fasteners that are not reused, and
those requiring thread locking compound, will be called out. The correct torque values must be used when installing
fasteners that require it. If the above conditions are not followed, parts or system damage could result.

Contents

GENERAL DESCRIPTION ................................... 6E-3

Notes for Working on Electrical Items ............... 6E-3
Symbols and Abbreviations ............................... 6E-9
Connector Inspecting Procedure ..................... 6E-11
Parts for Electrical Circuit ................................ 6E-12

DIAGNOSIS (4HE1-TC Only) ............................. 6E-15

Strategy-based Diagnostics............................. 6E-15
General Service Information............................ 6E-16
On-Board Diagnostic (OBD) ............................ 6E-16
Reading Diagnostic Trouble Codes Using a Tech 2 or 
Other Scan Tool .............................................. 6E-17
Typical Scan Data Values ............................... 6E-21
Troubleshooting............................................... 6E-21
Self-diagnosis Functions ................................. 6E-23
Diagnosis Trouble Code List ........................... 6E-25
Location of Sensor and Switch ........................ 6E-27
Parts Location.................................................. 6E-29
Engine Control Module (ECM)......................... 6E-30
Chart of Engine Control Module (ECM) Input/Output... 6E-31
Location of the Engine Control Module (ECM) Con-
nector............................................................... 6E-33
Location of Data Link Connector (DLC)........... 6E-33

BRIEF EXPLANATION OF EMISSION AND ELECTRI-
CAL CONTROL SYSTEM................................... 6E-35

MITICS (Mechanically Integrated Timing and Injection 
Control System)............................................... 6E-35
Governor (Model RLD-M) ................................ 6E-36
EGR (Exhaust Gas Recirculation) System ...... 6E-37
VSS (Variable Swirl System) ........................... 6E-39
Engine Control Module (ECM) System Wiring Dia-
gram ................................................................ 6E-40
Auxiliary Engine Control System ..................... 6E-41
Vacuum Switching Valve (VSV) Circuit ........... 6E-43
Exhaust Brake and Engine Warm-up Control.. 6E-45
DTC-P13 Engine Coolant Temperature (ECT) Sensor 
Circuit High Voltage......................................... 6E-46
DTC-P14 Engine Coolant Temperature (ECT) Sensor 
Circuit Low Voltage.......................................... 6E-50
DTC-P21 Rack Sensor Circuit Low Voltage .... 6E-54
DTC-P22 Rack Sensor Circuit High Voltage ... 6E-57
DTC-P23 Solenoid Switch Control Circuit Low Volt-
age................................................................... 6E-60
DTC-P24 Solenoid Switch Control Circuit High Volt-
age................................................................... 6E-64

DTC-P26 Quick Warm System (QWS) Relay Control 
Circuit High Voltage .........................................6E-68
DTC-P31 Exhaust Gas Recirculation (EGR) Electron-
ic Vacuum Regulating Valve (EVRV) Solenoid Control 
Low Voltage .....................................................6E-72
DTC-P32 Exhaust Gas Recirculation (EGR) Electron-
ic Vacuum Regulating Valve (EVRV) Solenoid Control 
High Voltage ....................................................6E-75
DTC-P33 Variable Swirl System (VSS) Control Circuit 
Low Voltage .....................................................6E-78
DTC-P34 Variable Swirl System (VSS) Control Circuit 
High Voltage ....................................................6E-82
DTC-P35 Exhaust Gas Recirculation (EGR) Quick 
Cut Vacuum Switching Valve (VSV) Control Circuit 
Low Voltage .....................................................6E-85
DTC-P36 Exhaust Gas Recirculation (EGR) Quick 
Cut Vacuum Switching Valve (VSV) Control Circuit 
High Voltage ....................................................6E-89
DTC-P41 Quick On Start (QOS) Relay Control Circuit 
Low Voltage .....................................................6E-92
DTC-P42 Quick On Start (QOS) Relay Control Circuit 
High Voltage ....................................................6E-96
DTC-P43 Aneroid Compensator Vacuum Switching 
Valve (VSV) Control Circuit Low Voltage.......6E-100
DTC-P44 Aneroid Compensator Vacuum Switching 
Valve (VSV) Control Circuit High Voltage ......6E-104
DTC-P45 Engine Speed Sensor Circuit Low Voltage.6E-108
DTC-P52 Electronically Erasable Programmable 
Read Only Memory (EEPROM) Error ............6E-112
DTC-P61 Barometric Pressure Sensor Circuit Error..6E-112

WITHOUT DIAGNOSIS TROUBLE CODE .......6E-113

Engine Hunting ..............................................6E-114
Startup Failure ...............................................6E-115
White Smoke (Excessive) ..............................6E-117
Black Smoke (Excessive) ..............................6E-119
Lack of Power ................................................6E-121
High Idle Engine Speed .................................6E-123
Solenoid Switch Malfunction ..........................6E-124
Exhaust Brake Malfunction ............................6E-125
EGR System Malfunction...............................6E-130
Variable Swirl System (VSS) System Malfunction (Equipped 
with Exhaust gas recirculation and VSS).................6E-133
Aneroid Compensator Malfunction.................6E-137
Quick Warm System (QWS) Malfunction.......6E-140

6E-2 EMISSION AND ELECTRICAL DIAGNOSIS

Fast Idle Control Device (FICD) System Malfunction.....6E-145

SPECIAL TOOLS.............................................. 6E-148
DIAGNOSIS (4HG1-T Only)..............................6E-150

Strategy-Based Diagnostics .......................... 6E-150

GENERAL SERVICE INFORMATION .............. 6E-151

Troubleshooting.............................................6E-152
Self-diagnosis Functions ...............................6E-152
Diagnosis Trouble Code (DTC) List...............6E-155
Location of Sensor and Switch ......................6E-156
Parts Location................................................6E-158
Engine Control Module (ECM).......................6E-159
Chart of Engine Control Module (ECM) Input/Output. 6E-160
Location of the Engine Control Module (ECM) Con-
nector.............................................................6E-161
Location of Data Link Connector (DLC).........6E-161
Engine Control Module (ECM) System Wiring Dia-
gram ..............................................................6E-163
Auxiliary Engine Control System (Equipped with Ex-
haust gas recirculation (EGR)) ......................6E-164
Vacuum Switching Valve (VSV) Circuit (Equipped 
with Exhaust gas recirculation (EGR))...........6E-165
Exhaust Brake Control...................................6E-166
DTC-13 Engine Coolant Temperature (ECT) Sensor 
Circuit High Voltage....................................... 6E-167
DTC-14 Engine Coolant Temperature (ECT) Sensor 
Circuit Low Voltage........................................6E-170
DTC-21 Rack Sensor Circuit Low Voltage ....6E-173
DTC-22 Rack Sensor Circuit High Voltage....6E-176
DTC-31 Exhaust Gas Recirculation (EGR) Vacuum Switch-
ing Valve (VSV) Solenoid Control Low Voltage ....6E-179
DTC-32 Exhaust Gas Recirculation (EGR) Vacuum Switch-
ing Valve (VSV) Solenoid Control High Voltage....6E-182
DTC-41 Quick On Start (QOS) Relay Control Circuit 
Low Voltage...................................................6E-185
DTC-42 Quick On Start (QOS) Relay Control Circuit 
High Voltage ..................................................6E-189
DTC-52 Electronically Erasable Programmable Read 
Only Memory (EEPROM) Error .....................6E-192

WITHOUT DIAGNOSIS TROUBLE CODE ....... 6E-193

Startup Failure (Quick On Start (QOS) only) . 6E-194
Black Smoke (Excessive) ..............................6E-196
Lack of Power................................................6E-198
Exhaust Brake Malfunction (Exhaust Brake only) . 6E-200
Exhaust Gas Recirculation (EGR) System Malfunc-
tion................................................................. 6E-206

SPECIAL TOOLS.............................................. 6E-209

EMISSION AND ELECTRICAL DIAGNOSIS 6E-3

GENERAL DESCRIPTION

The emission and electrical control system operates on
a 12 or 24 volt power supply with negative ground polar-
ity. Each wire in the vehicle is of a specific size and has
an identifying colored insulation.
These colors are indicated in wiring diagrams and will
help in tracing circuits and making proper connections. 
Wire size is determined by load capacity and circuit
length. Some wires are grouped together and taped. 
Such a grouping of wires is called a harness.

The harness use a split corrugated tube to protect the
wires from the elements. Each circuit consists of the fol-
lowing:

• Power source - the battery and the alternator.
• Wires - To carry electrical current through the cir-

cuit.

• Fuses - To protect the circuit against current over-

load.

• Relays - To protect voltage drop between the bat-

tery and the circuit parts and to protect the switch
points against burning.

• Switches - To open and close the circuit.
• Load - Any device, such as a light or a motor, which

converts the electrical current into useful work.

• Ground - To allow the current to flow back to the

power source.

In this manual, such electrical device is classified by
system. For major parts shown on the circuit based on
the circuit diagram for each system, inspection and re-
moval and installation procedures are detailed.

Notes for Working on Electrical Items

Battery Cable

Disconnecting the Battery Cable

1. All switches should be in the “OFF” position.
2. Disconnect the battery ground cable.
3. Disconnect the battery positive cable
4. Disconnect the battery cable (1).

Caution:
It is important that the battery ground cable be discon-
nected first.
Disconnecting the battery positive cable first can result
in a short circuit.

Connecting the Battery Cable
Follow the disconnecting procedure in the reverse or-
der.

Caution:
Clean the battery terminal and apply a light coat of
grease to prevent terminal corrosion.

Connecting Handling
Disconnecting the Connectors
Some connectors have a tang lock to hold the connec-
tors together during vehicle operation.

Legend

A. For 24 volt

1. Cable

Legend

A. For 12 volt

N6A1104E

N6A1105E