Content .. 744 745 746 747 ..

Isuzu N-Series. Manual - part 746

Engine Control System (4JH1) 6E-35

Attempt to start the engine.

Does the engine start and idle?

—

Go to Step 4

Go to Engine

Cranks but Does

Not Run

Select the DTC display function of the ECM.

Does the Tech 2 display any DTCs?

—

Go to Step 5

Go to Step 12

Turn OFF the ignition for 30 seconds.

Start the engine.

Monitor the DTC Information with the Tech 2.

Did you complete the action?

—

Go to Step 6

—

Does the Tech 2 display ECM DTC P0602?

—

Go to Applicable

DTC

Go to Step 7

Does the Tech 2 display ECM DTC P0251
(Symptom Code 9 or A), P0606 (Symptom Code A
or B) or P1605 (Symptom Code C, D or E)?

—

Go to Applicable

DTC

Go to Step 8

Does the Tech 2 display ECM DTC P0560
(Symptom Code 1, 2 or A)?

—

Go to Applicable

DTC

Go to Step 9

Does the Tech 2 display ECM DTC P0561
(Symptom Code A or B) or P1625 (Symptom Code
A or B)?

—

Go to Applicable

DTC

Go to Step 10

Does the Tech 2 display ECM DTC P1650
(Symptom Code A or B) or P1651 (Symptom Code
A or B)?

—

Go to Applicable

DTC

Go to Step 11

Is there any other code in any controller that has
not been diagnosed?

—

Go to Applicable

DTC

Go to Step 12

Review the following symptoms.

Refer to the applicable symptom diagnostic
table:

• Hard Start
• Rough, Unstable, or Incorrect Idle and

Stalling

• Cuts Out, Misses
• Surge/Chuggles
• Lack of Power, Sluggishness, or

Sponginess

• Hesitation, Sag, Stumble
• Fuel Knock/Combustion Noise
• Poor Fuel Economy
• Excessive Smoke (Black Smoke)
• Excessive Smoke (White Smoke)

Did you find and correct the condition?

—

System OK

Go to Intermittent

Conditions

Step

Action

Value(s)

Yes

6E-36 Engine Control System (4JH1)

Tech 2 Does Not Power Up

Circuit Description
The data link connector (DLC) is a standardized 16–
cavity connector. Connector design and location is
dictated by an industry wide standard, and is required
to provide the following:

• Tech 2 power battery positive voltage at terminal

16.

• Tech 2 power ground at terminal 4.

• Common signal ground at terminal 5.

The Tech 2 will power up with the ignition OFF. Some
modules however, will not communicate unless the
ignition is ON.

Tech 2 Does Not Power Up
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views

Step

Action

Value(s)

Yes

Important:
Make sure the Tech 2 works properly on another
vehicle before using this chart.

Turn OFF the ignition.

Inspect the ENG(B1)(B2) (15A) fuse (F-8 & F-
9) in the glove box fuse block.

Is the ENG(B1)(B2) (15A) fuse (F-8 & F-9) open?

—

Go to Step 2

Go to Step 3

Replace the ENG(B1)(B2) (15A) fuse (F-8 & F-9).
If the fuse continues to open, repair the short to
ground on one of the circuits that is fed by the
ENG(B1)(B2) (15A) fuse (F-8 & F-9) or replace the
shorted attached component fed by the
ENG(B1)(B2) (15A) fuse (F-8 & F-9).

Did you complete the repair?

—

Go to Step 7

—

Check each circuit at the data link connector
(DLC) (B-79 connector) for a backed out,
spread or missing terminal.

Repair the terminal as necessary.

Did you find and complete the repair?

—

Go to Step 7

Go to Step 4

Connect a test lamp between the B+ circuit (pin 16
of B-79 connector) at the DLC and a known
ground.

Does the test lamp illuminate?

—

Go to Step 6

Go to Step 5

Repair the open in the battery voltage circuit to the
DLC.

Did you complete the repair?

—

Go to Step 7

—

Test each ground circuit at the DLC (pins 4
and 5 of B-79 connector) for an open circuit or
high resistance.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 7

Go to Intermittent

Conditions

Connect the Tech 2 to the DLC.

Attempt to turn ON the Tech 2.

Does the Tech 2 ON?

—

System OK

Go to Step 1

Engine Control System (4JH1) 6E-37

Lost Communication with The Engine Control Module (ECM)

Circuit Description
The engine control module (ECM) communicates with
the Tech 2 over the Keyword 2000 serial data link.
However, the ECM and fuel injection pump control unit
(PCU) communicates with each other over the
controller area network (CAN) link. The CAN link is not
used for communication with the Tech 2 and is shared
only between the ECM and PCU.

Diagnostic Aids
The following conditions will cause a loss of Keyword
2000 serial data communication between the Tech 2
and any control module:

• A Keyword 2000 serial data circuit open.
• A Keyword 2000 serial data circuit shorted to

ground.

• A Keyword 2000 serial data circuit shorted to

voltage.

• An internal condition within a module or connector

on the Keyword 2000 serial data circuit, that
causes a short to voltage or ground to the Keyword
2000 serial data circuit.

• Open ground circuit (pin 5) at the DLC.

Lost Communication with The Engine Control
Module (ECM)
Schematic Reference: Engine Controls Schematics
Connector End View Reference: Engine Controls
Connector End Views or Engine Control Module (ECM)
Connector End Views

Step

Action

Value(s)

Yes

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic

System Check –

Engine Controls

Attempt to establish engine control module (ECM)
communications with the Tech 2.

Does the ECM communicate with the Tech 2?

—

Go to Step 3

Go to Step 4

Test the Keyword 2000 serial data circuit for an
intermittently short to ground or intermittently short
to voltage.

Did you find and correct the condition?

—

Go to Step 17

System OK

Check the ECM B-234 and B-233 connectors for
poor connections.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 5

Turn ON the ignition, with the engine OFF.

Check the Main (100A) (SBF-1), Key (50A)
(SBF-2) and ENG(B1)(B2) (15A) fuse (F-8 &
F-9). Replace and retest if open. If any fuse
continues to open, check for a short to ground
on each circuit fed by that fuse.

Turn OFF the ignition.

Disconnect the ECM B-234 harness
connector.

Turn ON the ignition, with the engine OFF.

Connect a test lamp to ground and check for
voltage at the ignition voltage supply circuit at
the ECM (pin 39 of B-234 connector).

Does the test lamp illuminate?

—

Go to Step 6

Go to Step 14

Test the data link connector (DLC) ground circuit at
terminal 5 for an open circuit or poor connection.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 7

Test the Keyword 2000 serial data circuit between
the ECM (pin 35 of B-234 connector) and the DLC
(pin 7 of B-79 connector) for a short to ground or
voltage.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 8

6E-38 Engine Control System (4JH1)

Important:
An open in a ground circuit at the ECM will not
cause a loss of communication.

Check ECM ground for corrosion and
tightness.

Clean or tighten grounds as necessary.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 9

Turn OFF the ignition.

Reconnect the ECM harness connector if
previously disconnected.

Turn ON the ignition, with the engine OFF.

Replace the ECM main relay with the horn
relay or replace with a known good relay.

Attempt to establish Tech 2 communications
with the ECM.

Does the ECM communicate with the Tech 2?

—

Go to Step 15

Go to Step 10

Turn OFF the ignition.

Remove the ECM main relay.

Turn ON the ignition, with the engine OFF.

Using a test lamp, check for battery voltage at
both of the battery voltage supply circuits to
the ECM main relay (pins 1 and 2 of X-14
connector).

Repair the open in the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 11

Reinstall the ECM main relay.

Turn the ignition ON and OFF while listening
or feeling for the ECM main relay click. Wait 2
seconds between transitions.

Does the ECM main relay click when the ignition is
turned ON or OFF?

—

Go to Step 13

Go to Step 12

Repair the ECM main relay control circuit between
the ECM main relay (pin 4 of X-14 connector) and
the ECM (pin 58 of B-234 connector) for the
following conditions:

• An open circuit
• A short to battery or ignition voltage
• High resistance or a poor connection at both

the ECM and ECM main relay

Did you find and correct the condition?

—

Go to Step 17

Go to Step 16

Check ECM main relay voltage supply circuit
to the ECM between the ECM main relay (pin
5 of X-14 connector) and the ECM (pin 3 of B-
234 connector) for the following conditions:

• An open circuit
• High resistance or a poor connection at

the ECM and ECM main relay

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 17

Go to Step 16

Repair the open in the ignition voltage circuit to the
ECM.

Did you complete the repair?

—

Go to Step 17

—

Step

Action

Value(s)

Yes

Content .. 744 745 746 747 ..