Isuzu N-Series. Manual - part 659

6E-58    Engine Control System (4HK1) 

Lost Communication with The Engine Control Module (ECM)

Circuit Description
The engine control module (ECM), transmission control
module (TCM) and supplemental restraint system
(SRS) control module communicates with the Tech 2
over the Keyword 2000 serial data link. The hill start aid
(HSA) control module communicates with the Keyword
82 serial data link. However, the ECM, TCM, electric
hydraulic control module (EHCU) (ABS module) and
the data recording module (DRM) communicate 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 among each module.

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

No

1

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic 

System Check – 

Engine Controls

2

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

Does the ECM communicate with the Tech 2?

—

Go to Intermittent 

Conditions

Go to Step 3

3

Check the ECM E-111 and J-191 connectors for
poor connections.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 4

4

1.

Turn ON the ignition, with the engine OFF.

2.

Check the ECM (40A) slow blow fuse, ECM
(10A) fuse and Engine (IG) (10A) fuse.
Replace and retest if open. If any fuse
continues to open, check for a short to ground
on each circuit fed by that fuse.

3.

Turn OFF the ignition.

4.

Disconnect the ECM J-191 harness
connector.

5.

Turn ON the ignition, with the engine OFF.

6.

Connect a test lamp to ground and check for
voltage at the ignition voltage supply circuit at
the ECM (pin 24 of J-191 connector).

Does the test lamp illuminate?

—

Go to Step 5

Go to Step 12

5

1.

Turn OFF the ignition.

2.

Connect a DMM between the Keyword serial
data circuit at the ECM (pin 38 of J-191
connector) and the data link connector (DLC)
(pin 7 of B-79 connector).

3.

Test the circuits for an open circuit or high
resistance.

4.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 6

6

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

1.

Check ECM ground for corrosion and
tightness.

2.

Clean or tighten grounds as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 7

 Engine Control System (4HK1)    6E-59

7

1.

Turn OFF the ignition.

2.

Reconnect the ECM harness connector if
previously disconnected.

3.

Turn ON the ignition, with the engine OFF.

4.

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

5.

Attempt to establish Tech 2 communications
with the ECM.

Does the ECM communicate with the Tech 2?

—

Go to Step 13

Go to Step 8

8

1.

Turn OFF the ignition.

2.

Remove the ECM main relay.

3.

Turn ON the ignition, with the engine OFF.

4.

Using a test lamp, check for battery voltage at
both of the battery voltage supply circuits to
the ECM main relay (pins 3 and 4 of X-18
connector).

5.

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

Did you find and correct the condition?

—

Go to Step 15

Go to Step 9

9

1.

Reinstall the ECM main relay.

2.

Turn the ignition ON and OFF while listening
or feeling for the ECM main relay click. Wait 7
seconds between transitions.

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

—

Go to Step 11

Go to Step 10

10

Repair the ECM main relay ground circuit between
the ECM main relay (pin 5 of X-18 connector) and
chassis ground terminal (J-9) for the following
conditions:

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

main relay and ground terminal

Did you complete the repair?

—

Go to Step 15

—

11

1.

Test the ECM main relay voltage feed circuit to
the ECM (pins 2 and 5 of J-191 connector) for
the following conditions:

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

ECM and ECM main relay

2.

Repair the circuit(s) as necessary.

Did you find and correct the condition?

—

Go to Step 15

Go to Step 14

12

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

Did you complete the repair?

—

Go to Step 15

—

13

Replace the ECM main relay.

Did you complete the replacement?

—

Go to Step 15

—

14

Important:
Replacement ECM must be programmed.

Replace the ECM. Refer to Engine Control Module
(ECM) Replacement / Fuel Injector ID Code Data
Programming in this section.

Did you complete the replacement?

—

Go to Step 15

—

Step

Action

Value(s)

Yes

No

6E-60    Engine Control System (4HK1) 

15

1.

Turn OFF the ignition.

2.

Reconnect all previously disconnected fuse,
relay and harness connector(s).

3.

Turn the ignition ON with the engine OFF.

4.

Attempt to establish Tech 2 communications
with the ECM.

Does the Tech 2 communicate with the ECM?

—

System OK

Go to Step 3

Step

Action

Value(s)

Yes

No

 Engine Control System (4HK1)    6E-61

Engine Cranks but Does Not Run

Description
The Engine Cranks but Does Not Run diagnostic table
is an organized approach to identifying a condition that
causes an engine to not start. The diagnostic table
directs the service technician to the appropriate system
diagnosis. The diagnostic table assumes the following
conditions are met:

• The battery is completely charged and terminals

are cleaned and tight.

• The engine cranking speed is normal.
• There is adequate fuel in the fuel tank.
• There is no fuel leak in the fuel line.
• There is no air in the fuel line.
• Filters (Air, Fuel) are clean.
• Fuse and slow blow fuse are normal.

Notice:

• The engine will start even if exhuast brake is fully

engage.

Diagnostic Aid
If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.

Test Description
The numbers below refers to the step number on the
diagnostic table.
5. If the fuel rail pressure (FRP) regulator low control
circuits between the ECM and the FRP regulator are
shorted to ground, FRP Regulator Feedback will be
approximately 300 mA or more low as compared with
normal.

Engine Cranks but Does Not Run
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

No

1

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic 

System Check – 

Engine Controls

2

1.

Install the Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Crank the engine for specified amount of time.

4.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

Does the Tech 2 display any DTCs that failed this
ignition?

15 seconds

Go to Diagnostic 

Trouble Code (DTC) 

List

Go to Step 3

3

1.

Turn OFF the ignition.

2.

Wait 2 minutes for the fuel pressure to bleed
down from the fuel rail.

3.

Turn ON the ignition, with the engine OFF. DO
NOT start the engine.

4.

Observe the Fuel Rail Pressure (FRP) Sensor
parameter with a Tech 2.

Is the FRP Sensor parameter the specified value?

0.9 – 1.0 Volts

Go to Step 4

Go to Step 6

4

Notice:
If the vehicle has run out of fuel, air may be trapped
in the fuel system.

1.

Make sure the fuel tank(s) have adequate fuel
and the fuel quality is good (take a sample).

2.

Observe the FRP Sensor parameter on the
Tech 2 while cranking over the engine for 5
seconds.

Does the FRP Sensor reach the specified value
during crank?

1.4 Volts

Go to Step 9

Go to Step 5