Isuzu KB P190. Manual — part 820

The engine management diagnostic procedure is organised in a logical structure that begins with the Diagnostic System
Check. The Diagnostic System Check directs the diagnostic procedure to the logical steps necessary to diagnose an
engine driveability fault condition.

1.2

Diagnostic Trouble Code Tables

The Diagnostic System Check directs the diagnostic procedure to the appropriate diagnostic trouble code (DTC) tables
if there is a DTC currently stored in the engine control module (ECM).

The diagnostic tables locate a faulty circuit or component through a logic based on the process of elimination. These
diagnostic tables are developed with the following assumptions:

•

the vehicle functioned correctly at the time of assembly,

•

there are no multiple faults, and

•

the problem currently exists.

Understanding and the correct use of the diagnostic tables are essential to reduce diagnostic time and to prevent
misdiagnosis.

Multiple DTC Fault Conditions

Some fault conditions trigger multiple component DTCs even if the fault condition exists only on a single component. If
there are multiple DTCs stored in the ECM, the service technician must view and record all DTCs logged.

The relationship between the logged DTCs can then be analysed to determine the source of the fault condition. Always
begin the diagnostic process with the DTC table of the fault condition that may trigger other DTCs to set.

The following fault conditions may trigger multiple DTCs:

•

a fault in the serial data communication circuit,

•

a system voltage that is too low may cause incorrect engine management system operation or engine
management component malfunction,

•

a system voltage that is too high may damage the ECM and/or other engine management components,

•

fault condition in the ECM read only memory (ROM) or random access memory (RAM),

•

fault condition in the ECM internal circuitry or programming,

•

improperly connected sensor or component wiring connector, or

•

an electrical fault condition in the following shared ECM electrical circuits trigger DTCs on components or sensors
that share in the faulty shared circuit. Test the electrical circuit of the appropriate sensors or components to isolate
the fault condition. Refer to 3 Wiring Diagrams and Connector Charts in this Section.

•

5 V Reference Circuit,

•

Low Reference Circuit, or

•

Ignition Control Voltage Circuit.

If there are no obvious faults to begin a multiple DTC fault condition diagnostic procedure, diagnose the DTCs in the
following order unless directed otherwise:

Always start with the lowest numbered component level DTCs such as:

•

sensor DTCs,

•

solenoid DTCs, or

•

relay DTCs.

Then follow with system level DTCs such as:

•

misfire DTCs,

Engine Management – V6 – Diagnostics

Page 6C1-2–5

•

fuel trim DTCs, or

•

catalyst DTCs.

1.3 Symptoms

Diagnostics

The Diagnostic System Check directs the service technician to the symptoms diagnostics if the following conditions
exist:

•

a vehicle driveability fault condition exists,

•

there is no current diagnostic trouble code presently stored in the ECM, and

•

all Tech 2 engine data parameters are within normal operating range.

1.4

Diagnostic Trouble Codes

The ECM constantly performs self-diagnostic tests on the engine management system. When the ECM detects a fault
condition in the engine operating parameters, the ECM sets a diagnostic trouble code (DTC) to represent that fault
condition. The following are the types of DTCs programmed in the ECM. In addition, DTCs are classified as either a
current or history DTC.

•

Type A – emission related DTCs,

•

Type B – emission related DTCs, and

•

Type C – non-emission related DTCs.

N O T E

Depending on the type of DTC set, the ECM may
command the malfunction indicator lamp (MIL) to
illuminate and warn the driver there is a fault in
the engine management system.

Type A – Emission Related DTCs

The ECM takes the following action when a Type A DTC runs and fails:

•

sets a current Type A DTC that represents the fault condition,

•

illuminates the instrument cluster malfunction indicator lamp (MIL), and

•

records the operating condition at the time the diagnostic fails and stores this information in the freeze frame
failure record.

Type B – Emission Related DTCs

The ECM takes the following action when a Type B DTC runs and fails:

•

On the first time a Type B DTC fails, the ECM takes the following actions:

−

sets a current Type B DTC that represents the fault condition, and

−

records the operating conditions at the time the fault sets and stores this information in the failure records.

•

On the second consecutive ignition cycle that a Type B DTC fails, the ECM takes the following actions:

−

activates the instrument cluster malfunction indicator lamp (MIL), and

−

records the operating condition at the time the diagnostic fails and stores this information in the freeze frame
failure record.

Conditions for Clearing Type A or Type B DTCs

•

The current DTC clears when there is no fault condition in the current ECM self-diagnostics.

•

If there are no DTCs logged after three or four consecutive ignition cycles, the ECM deactivates the instrument
cluster malfunction indicator lamp (MIL).

•

Type A or Type B History DTC clears when there is no fault condition after 40 consecutive warm-up cycles.

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Isuzu KB P190. Manual — part 820

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